| Message ID | 20221031113742.26480-4-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | nfsd: clean up refcounting in the filecache | expand |
> On Oct 31, 2022, at 7:37 AM, Jeff Layton <jlayton@kernel.org> wrote: > > The filecache refcounting is a bit non-standard for something searchable > by RCU, in that we maintain a sentinel reference while it's hashed. This > in turn requires that we have to do things differently in the "put" > depending on whether its hashed, which we believe to have led to races. > > There are other problems in here too. nfsd_file_close_inode_sync can end > up freeing an nfsd_file while there are still outstanding references to > it, and there are a number of subtle ToC/ToU races. > > Rework the code so that the refcount is what drives the lifecycle. When > the refcount goes to zero, then unhash and rcu free the object. > > With this change, the LRU carries a reference. Take special care to > deal with it when removing an entry from the list. ....removing an entry from the dispose list, or the LRU? I spent today reviewing and testing this series, and comparing its behavior to the behavior of the current code base. A few general comments below: > Signed-off-by: Jeff Layton <jlayton@kernel.org> > --- > fs/nfsd/filecache.c | 247 +++++++++++++++++++++----------------------- > fs/nfsd/trace.h | 1 + > 2 files changed, 121 insertions(+), 127 deletions(-) > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index ce80b6a80ffc..d928c5e38eeb 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -1,6 +1,12 @@ > // SPDX-License-Identifier: GPL-2.0 > /* > * The NFSD open file cache. > + * > + * Each nfsd_file is created in response to client activity -- either regular > + * file I/O for v2/v3, or opening a file for v4. Files opened via v4 are > + * cleaned up as soon as their refcount goes to 0. Entries for v2/v3 are > + * flagged with NFSD_FILE_GC. On their last put, they are added to the LRU for > + * eventual disposal if they aren't used again within a short time period. Trond and I discussed intentionally not using the terms "v4-only" and "v2/3" in the filecache comments and function names. That's why the flag is called GC and not, say, NFSV3. Can the new comments stick with gc and nogc? > */ > > #include <linux/hash.h> > @@ -301,8 +307,7 @@ nfsd_file_alloc(struct nfsd_file_lookup_key *key, unsigned int may) > if (key->gc) > __set_bit(NFSD_FILE_GC, &nf->nf_flags); > nf->nf_inode = key->inode; > - /* nf_ref is pre-incremented for hash table */ > - refcount_set(&nf->nf_ref, 2); > + refcount_set(&nf->nf_ref, 1); > nf->nf_may = key->need; > nf->nf_mark = NULL; > } > @@ -351,23 +356,25 @@ nfsd_file_unhash(struct nfsd_file *nf) > return false; > } > There's still no explanation in the code of why writeback is needed for GC files. I can write a patch to add that, say, right here as a documenting comment for nfsd_file_free, if you agree. > -static bool > +static void > nfsd_file_free(struct nfsd_file *nf) > { > s64 age = ktime_to_ms(ktime_sub(ktime_get(), nf->nf_birthtime)); > - bool flush = false; > + > + trace_nfsd_file_free(nf); Maybe move this tracepoint in 2/5 instead? Or just leave it where it was. Up to you. > > this_cpu_inc(nfsd_file_releases); > this_cpu_add(nfsd_file_total_age, age); > > - trace_nfsd_file_free(nf); > + nfsd_file_unhash(nf); > + nfsd_file_fsync(nf); > + > if (nf->nf_mark) > nfsd_file_mark_put(nf->nf_mark); > if (nf->nf_file) { > get_file(nf->nf_file); > filp_close(nf->nf_file, NULL); > fput(nf->nf_file); > - flush = true; > } > > /* > @@ -375,10 +382,9 @@ nfsd_file_free(struct nfsd_file *nf) > * WARN and leak it to preserve system stability. > */ > if (WARN_ON_ONCE(!list_empty(&nf->nf_lru))) > - return flush; > + return; > > call_rcu(&nf->nf_rcu, nfsd_file_slab_free); > - return flush; > } > > static bool > @@ -394,17 +400,23 @@ nfsd_file_check_writeback(struct nfsd_file *nf) > mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK); > } > > -static void nfsd_file_lru_add(struct nfsd_file *nf) > +static bool nfsd_file_lru_add(struct nfsd_file *nf) > { > set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > - if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) > + if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) { > trace_nfsd_file_lru_add(nf); > + return true; > + } > + return false; > } > > -static void nfsd_file_lru_remove(struct nfsd_file *nf) > +static bool nfsd_file_lru_remove(struct nfsd_file *nf) > { > - if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) > + if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) { > trace_nfsd_file_lru_del(nf); > + return true; > + } > + return false; > } > > struct nfsd_file * > @@ -415,86 +427,77 @@ nfsd_file_get(struct nfsd_file *nf) > return NULL; > } > > -static void > +/** > + * nfsd_file_unhash_and_queue - unhash a file and queue it to the dispose list > + * @nf: nfsd_file to be unhashed and queued > + * @dispose: list to which it should be queued > + * > + * Attempt to unhash a nfsd_file and queue it to the given list. Each file > + * will have a reference held on behalf of the list. That reference may come > + * from the LRU, or we may need to take one. If we can't get a reference, > + * ignore it altogether. > + */ > +static bool > nfsd_file_unhash_and_queue(struct nfsd_file *nf, struct list_head *dispose) > { > trace_nfsd_file_unhash_and_queue(nf); > if (nfsd_file_unhash(nf)) { > - /* caller must call nfsd_file_dispose_list() later */ > - nfsd_file_lru_remove(nf); > + /* > + * If we remove it from the LRU, then just use that > + * reference for the dispose list. Otherwise, we need > + * to take a reference. If that fails, just ignore > + * the file altogether. > + */ > + if (!nfsd_file_lru_remove(nf) && !nfsd_file_get(nf)) > + return false; > list_add(&nf->nf_lru, dispose); > + return true; > } > + return false; > } > > -static void > -nfsd_file_put_noref(struct nfsd_file *nf) > -{ > - trace_nfsd_file_put(nf); > - > - if (refcount_dec_and_test(&nf->nf_ref)) { > - WARN_ON(test_bit(NFSD_FILE_HASHED, &nf->nf_flags)); > - nfsd_file_lru_remove(nf); > - nfsd_file_free(nf); > - } > -} > - > -static void > -nfsd_file_unhash_and_put(struct nfsd_file *nf) > -{ > - if (nfsd_file_unhash(nf)) > - nfsd_file_put_noref(nf); > -} > - > +/** > + * nfsd_file_put - put the reference to a nfsd_file > + * @nf: nfsd_file of which to put the reference > + * > + * Put a reference to a nfsd_file. In the v4 case, we just put the > + * reference immediately. In the v2/3 case, if the reference would be > + * the last one, the put it on the LRU instead to be cleaned up later. > + */ > void > nfsd_file_put(struct nfsd_file *nf) > { > - might_sleep(); The might_sleep() annotation should be added back to nfsd_file_fsync() or its callers. It might give more useful warnings if you were to annotate the external API functions (as was done here) rather than internal helper functions. > - > - if (test_bit(NFSD_FILE_GC, &nf->nf_flags)) > - nfsd_file_lru_add(nf); > - else if (refcount_read(&nf->nf_ref) == 2) > - nfsd_file_unhash_and_put(nf); > - > - if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > - nfsd_file_fsync(nf); > - nfsd_file_put_noref(nf); > - } else if (nf->nf_file && test_bit(NFSD_FILE_GC, &nf->nf_flags)) { > - nfsd_file_put_noref(nf); > - nfsd_file_schedule_laundrette(); This might be the only caller of nfsd_file_schedule_laundrette. How does the laundrette get scheduled now? > - } else > - nfsd_file_put_noref(nf); > -} > - > -static void > -nfsd_file_dispose_list(struct list_head *dispose) > -{ > - struct nfsd_file *nf; > + trace_nfsd_file_put(nf); > > - while(!list_empty(dispose)) { > - nf = list_first_entry(dispose, struct nfsd_file, nf_lru); > - list_del_init(&nf->nf_lru); > - nfsd_file_fsync(nf); > - nfsd_file_put_noref(nf); > + /* > + * The HASHED check is racy. We may end up with the occasional > + * unhashed entry on the LRU, but they should get cleaned up > + * like any other. > + */ > + if (test_bit(NFSD_FILE_GC, &nf->nf_flags) && > + test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > + /* > + * If this is the last reference (nf_ref == 1), then transfer > + * it to the LRU. If the add to the LRU fails, just put it as > + * usual. > + */ > + if (refcount_dec_not_one(&nf->nf_ref) || nfsd_file_lru_add(nf)) > + return; > } > + if (refcount_dec_and_test(&nf->nf_ref)) > + nfsd_file_free(nf); > } > > static void > -nfsd_file_dispose_list_sync(struct list_head *dispose) > +nfsd_file_dispose_list(struct list_head *dispose) > { > - bool flush = false; > struct nfsd_file *nf; > > while(!list_empty(dispose)) { > nf = list_first_entry(dispose, struct nfsd_file, nf_lru); > list_del_init(&nf->nf_lru); > - nfsd_file_fsync(nf); > - if (!refcount_dec_and_test(&nf->nf_ref)) > - continue; > - if (nfsd_file_free(nf)) > - flush = true; > + nfsd_file_free(nf); > } > - if (flush) > - flush_delayed_fput(); > } > > static void > @@ -564,21 +567,8 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > struct list_head *head = arg; > struct nfsd_file *nf = list_entry(item, struct nfsd_file, nf_lru); > > - /* > - * Do a lockless refcount check. The hashtable holds one reference, so > - * we look to see if anything else has a reference, or if any have > - * been put since the shrinker last ran. Those don't get unhashed and > - * released. > - * > - * Note that in the put path, we set the flag and then decrement the > - * counter. Here we check the counter and then test and clear the flag. > - * That order is deliberate to ensure that we can do this locklessly. > - */ > - if (refcount_read(&nf->nf_ref) > 1) { > - list_lru_isolate(lru, &nf->nf_lru); > - trace_nfsd_file_gc_in_use(nf); > - return LRU_REMOVED; > - } > + /* We should only be dealing with v2/3 entries here */ > + WARN_ON_ONCE(!test_bit(NFSD_FILE_GC, &nf->nf_flags)); > > /* > * Don't throw out files that are still undergoing I/O or > @@ -589,40 +579,30 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > return LRU_SKIP; > } > > + /* If it was recently added to the list, skip it */ > if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags)) { > trace_nfsd_file_gc_referenced(nf); > return LRU_ROTATE; > } > > - if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > - trace_nfsd_file_gc_hashed(nf); > - return LRU_SKIP; > + /* > + * Put the reference held on behalf of the LRU. If it wasn't the last > + * one, then just remove it from the LRU and ignore it. > + */ > + if (!refcount_dec_and_test(&nf->nf_ref)) { > + trace_nfsd_file_gc_in_use(nf); > + list_lru_isolate(lru, &nf->nf_lru); > + return LRU_REMOVED; > } > > + /* Refcount went to zero. Unhash it and queue it to the dispose list */ > + nfsd_file_unhash(nf); > list_lru_isolate_move(lru, &nf->nf_lru, head); > this_cpu_inc(nfsd_file_evictions); > trace_nfsd_file_gc_disposed(nf); > return LRU_REMOVED; > } > > -/* > - * Unhash items on @dispose immediately, then queue them on the > - * disposal workqueue to finish releasing them in the background. > - * > - * cel: Note that between the time list_lru_shrink_walk runs and > - * now, these items are in the hash table but marked unhashed. > - * Why release these outside of lru_cb ? There's no lock ordering > - * problem since lru_cb currently takes no lock. > - */ > -static void nfsd_file_gc_dispose_list(struct list_head *dispose) > -{ > - struct nfsd_file *nf; > - > - list_for_each_entry(nf, dispose, nf_lru) > - nfsd_file_hash_remove(nf); > - nfsd_file_dispose_list_delayed(dispose); > -} > - > static void > nfsd_file_gc(void) > { > @@ -632,7 +612,7 @@ nfsd_file_gc(void) > ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb, > &dispose, list_lru_count(&nfsd_file_lru)); > trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru)); > - nfsd_file_gc_dispose_list(&dispose); > + nfsd_file_dispose_list_delayed(&dispose); > } > > static void > @@ -657,7 +637,7 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc) > ret = list_lru_shrink_walk(&nfsd_file_lru, sc, > nfsd_file_lru_cb, &dispose); > trace_nfsd_file_shrinker_removed(ret, list_lru_count(&nfsd_file_lru)); > - nfsd_file_gc_dispose_list(&dispose); > + nfsd_file_dispose_list_delayed(&dispose); > return ret; > } > > @@ -668,8 +648,11 @@ static struct shrinker nfsd_file_shrinker = { > }; > > /* > - * Find all cache items across all net namespaces that match @inode and > - * move them to @dispose. The lookup is atomic wrt nfsd_file_acquire(). > + * Find all cache items across all net namespaces that match @inode, unhash > + * them, take references and then put them on @dispose if that was successful. > + * > + * The nfsd_file objects on the list will be unhashed, and each will have a > + * reference taken. > */ > static unsigned int > __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > @@ -687,8 +670,9 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > nfsd_file_rhash_params); > if (!nf) > break; > - nfsd_file_unhash_and_queue(nf, dispose); > - count++; > + > + if (nfsd_file_unhash_and_queue(nf, dispose)) > + count++; > } while (1); > rcu_read_unlock(); > return count; > @@ -700,15 +684,25 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > * > * Unhash and put all cache item associated with @inode. > */ > -static void > +static unsigned int > nfsd_file_close_inode(struct inode *inode) > { > - LIST_HEAD(dispose); > + struct nfsd_file *nf; > unsigned int count; > + LIST_HEAD(dispose); > > count = __nfsd_file_close_inode(inode, &dispose); > trace_nfsd_file_close_inode(inode, count); > - nfsd_file_dispose_list_delayed(&dispose); > + if (count) { Why is it necessary to check @count? I would think that the the empty list check would be sufficient. > + while(!list_empty(&dispose)) { > + nf = list_first_entry(&dispose, struct nfsd_file, nf_lru); > + list_del_init(&nf->nf_lru); > + trace_nfsd_file_closing(nf); > + if (refcount_dec_and_test(&nf->nf_ref)) > + nfsd_file_free(nf); > + } > + } > + return count; > } > > /** > @@ -720,19 +714,15 @@ nfsd_file_close_inode(struct inode *inode) > void > nfsd_file_close_inode_sync(struct inode *inode) > { > - LIST_HEAD(dispose); > - unsigned int count; > - > - count = __nfsd_file_close_inode(inode, &dispose); > - trace_nfsd_file_close_inode_sync(inode, count); > - nfsd_file_dispose_list_sync(&dispose); > + if (nfsd_file_close_inode(inode)) > + flush_delayed_fput(); > } > > /** > * nfsd_file_delayed_close - close unused nfsd_files > * @work: dummy > * > - * Walk the LRU list and close any entries that have not been used since > + * Walk the LRU list and destroy any entries that have not been used since > * the last scan. > */ > static void > @@ -1054,8 +1044,10 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > rcu_read_lock(); > nf = rhashtable_lookup(&nfsd_file_rhash_tbl, &key, > nfsd_file_rhash_params); > - if (nf) > - nf = nfsd_file_get(nf); > + if (nf) { > + if (!nfsd_file_lru_remove(nf)) > + nf = nfsd_file_get(nf); > + } > rcu_read_unlock(); > if (nf) > goto wait_for_construction; > @@ -1090,11 +1082,11 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > goto out; > } > open_retry = false; > - nfsd_file_put_noref(nf); > + if (refcount_dec_and_test(&nf->nf_ref)) > + nfsd_file_free(nf); > goto retry; > } > > - nfsd_file_lru_remove(nf); > this_cpu_inc(nfsd_file_cache_hits); > > status = nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_flags)); > @@ -1104,7 +1096,8 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > this_cpu_inc(nfsd_file_acquisitions); > *pnf = nf; > } else { > - nfsd_file_put(nf); > + if (refcount_dec_and_test(&nf->nf_ref)) > + nfsd_file_free(nf); > nf = NULL; > } > > @@ -1131,7 +1124,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > * then unhash. > */ > if (status != nfs_ok || key.inode->i_nlink == 0) > - nfsd_file_unhash_and_put(nf); > + nfsd_file_unhash(nf); > clear_bit_unlock(NFSD_FILE_PENDING, &nf->nf_flags); > smp_mb__after_atomic(); > wake_up_bit(&nf->nf_flags, NFSD_FILE_PENDING); > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h > index 940252482fd4..a44ded06af87 100644 > --- a/fs/nfsd/trace.h > +++ b/fs/nfsd/trace.h > @@ -906,6 +906,7 @@ DEFINE_EVENT(nfsd_file_class, name, \ > DEFINE_NFSD_FILE_EVENT(nfsd_file_free); > DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash); > DEFINE_NFSD_FILE_EVENT(nfsd_file_put); > +DEFINE_NFSD_FILE_EVENT(nfsd_file_closing); > DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash_and_queue); > > TRACE_EVENT(nfsd_file_alloc, > -- > 2.38.1 > -- Chuck Lever
On Mon, 2022-10-31 at 20:45 +0000, Chuck Lever III wrote: > > > On Oct 31, 2022, at 7:37 AM, Jeff Layton <jlayton@kernel.org> wrote: > > > > The filecache refcounting is a bit non-standard for something searchable > > by RCU, in that we maintain a sentinel reference while it's hashed. This > > in turn requires that we have to do things differently in the "put" > > depending on whether its hashed, which we believe to have led to races. > > > > There are other problems in here too. nfsd_file_close_inode_sync can end > > up freeing an nfsd_file while there are still outstanding references to > > it, and there are a number of subtle ToC/ToU races. > > > > Rework the code so that the refcount is what drives the lifecycle. When > > the refcount goes to zero, then unhash and rcu free the object. > > > > With this change, the LRU carries a reference. Take special care to > > deal with it when removing an entry from the list. > > ....removing an entry from the dispose list, or the LRU? > > I spent today reviewing and testing this series, and > comparing its behavior to the behavior of the current > code base. A few general comments below: > Thanks for the review! > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > --- > > fs/nfsd/filecache.c | 247 +++++++++++++++++++++----------------------- > > fs/nfsd/trace.h | 1 + > > 2 files changed, 121 insertions(+), 127 deletions(-) > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > index ce80b6a80ffc..d928c5e38eeb 100644 > > --- a/fs/nfsd/filecache.c > > +++ b/fs/nfsd/filecache.c > > @@ -1,6 +1,12 @@ > > // SPDX-License-Identifier: GPL-2.0 > > /* > > * The NFSD open file cache. > > + * > > + * Each nfsd_file is created in response to client activity -- either regular > > + * file I/O for v2/v3, or opening a file for v4. Files opened via v4 are > > + * cleaned up as soon as their refcount goes to 0. Entries for v2/v3 are > > + * flagged with NFSD_FILE_GC. On their last put, they are added to the LRU for > > + * eventual disposal if they aren't used again within a short time period. > > Trond and I discussed intentionally not using the terms "v4-only" > and "v2/3" in the filecache comments and function names. That's > why the flag is called GC and not, say, NFSV3. Can the new comments > stick with gc and nogc? > This comment is explaining that v2/v3 _are_ GC entries. I can just remove this comment I guess, but converting all the mentions to gc/non- gc in this comment will make it nonsensical. > > > */ > > > > #include <linux/hash.h> > > @@ -301,8 +307,7 @@ nfsd_file_alloc(struct nfsd_file_lookup_key *key, unsigned int may) > > if (key->gc) > > __set_bit(NFSD_FILE_GC, &nf->nf_flags); > > nf->nf_inode = key->inode; > > - /* nf_ref is pre-incremented for hash table */ > > - refcount_set(&nf->nf_ref, 2); > > + refcount_set(&nf->nf_ref, 1); > > nf->nf_may = key->need; > > nf->nf_mark = NULL; > > } > > @@ -351,23 +356,25 @@ nfsd_file_unhash(struct nfsd_file *nf) > > return false; > > } > > > > There's still no explanation in the code of why writeback is > needed for GC files. I can write a patch to add that, say, > right here as a documenting comment for nfsd_file_free, if > you agree. > > I'll add something here. > > -static bool > > +static void > > nfsd_file_free(struct nfsd_file *nf) > > { > > s64 age = ktime_to_ms(ktime_sub(ktime_get(), nf->nf_birthtime)); > > - bool flush = false; > > + > > + trace_nfsd_file_free(nf); > > Maybe move this tracepoint in 2/5 instead? Or just leave it > where it was. Up to you. > Sure, done. > > > > > this_cpu_inc(nfsd_file_releases); > > this_cpu_add(nfsd_file_total_age, age); > > > > - trace_nfsd_file_free(nf); > > + nfsd_file_unhash(nf); > > + nfsd_file_fsync(nf); > > + > > if (nf->nf_mark) > > nfsd_file_mark_put(nf->nf_mark); > > if (nf->nf_file) { > > get_file(nf->nf_file); > > filp_close(nf->nf_file, NULL); > > fput(nf->nf_file); > > - flush = true; > > } > > > > /* > > @@ -375,10 +382,9 @@ nfsd_file_free(struct nfsd_file *nf) > > * WARN and leak it to preserve system stability. > > */ > > if (WARN_ON_ONCE(!list_empty(&nf->nf_lru))) > > - return flush; > > + return; > > > > call_rcu(&nf->nf_rcu, nfsd_file_slab_free); > > - return flush; > > } > > > > static bool > > @@ -394,17 +400,23 @@ nfsd_file_check_writeback(struct nfsd_file *nf) > > mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK); > > } > > > > -static void nfsd_file_lru_add(struct nfsd_file *nf) > > +static bool nfsd_file_lru_add(struct nfsd_file *nf) > > { > > set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); > > - if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) > > + if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) { > > trace_nfsd_file_lru_add(nf); > > + return true; > > + } > > + return false; > > } > > > > -static void nfsd_file_lru_remove(struct nfsd_file *nf) > > +static bool nfsd_file_lru_remove(struct nfsd_file *nf) > > { > > - if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) > > + if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) { > > trace_nfsd_file_lru_del(nf); > > + return true; > > + } > > + return false; > > } > > > > struct nfsd_file * > > @@ -415,86 +427,77 @@ nfsd_file_get(struct nfsd_file *nf) > > return NULL; > > } > > > > -static void > > +/** > > + * nfsd_file_unhash_and_queue - unhash a file and queue it to the dispose list > > + * @nf: nfsd_file to be unhashed and queued > > + * @dispose: list to which it should be queued > > + * > > + * Attempt to unhash a nfsd_file and queue it to the given list. Each file > > + * will have a reference held on behalf of the list. That reference may come > > + * from the LRU, or we may need to take one. If we can't get a reference, > > + * ignore it altogether. > > + */ > > +static bool > > nfsd_file_unhash_and_queue(struct nfsd_file *nf, struct list_head *dispose) > > { > > trace_nfsd_file_unhash_and_queue(nf); > > if (nfsd_file_unhash(nf)) { > > - /* caller must call nfsd_file_dispose_list() later */ > > - nfsd_file_lru_remove(nf); > > + /* > > + * If we remove it from the LRU, then just use that > > + * reference for the dispose list. Otherwise, we need > > + * to take a reference. If that fails, just ignore > > + * the file altogether. > > + */ > > + if (!nfsd_file_lru_remove(nf) && !nfsd_file_get(nf)) > > + return false; > > list_add(&nf->nf_lru, dispose); > > + return true; > > } > > + return false; > > } > > > > -static void > > -nfsd_file_put_noref(struct nfsd_file *nf) > > -{ > > - trace_nfsd_file_put(nf); > > - > > - if (refcount_dec_and_test(&nf->nf_ref)) { > > - WARN_ON(test_bit(NFSD_FILE_HASHED, &nf->nf_flags)); > > - nfsd_file_lru_remove(nf); > > - nfsd_file_free(nf); > > - } > > -} > > - > > -static void > > -nfsd_file_unhash_and_put(struct nfsd_file *nf) > > -{ > > - if (nfsd_file_unhash(nf)) > > - nfsd_file_put_noref(nf); > > -} > > - > > +/** > > + * nfsd_file_put - put the reference to a nfsd_file > > + * @nf: nfsd_file of which to put the reference > > + * > > + * Put a reference to a nfsd_file. In the v4 case, we just put the > > + * reference immediately. In the v2/3 case, if the reference would be > > + * the last one, the put it on the LRU instead to be cleaned up later. > > + */ > > void > > nfsd_file_put(struct nfsd_file *nf) > > { > > - might_sleep(); > > The might_sleep() annotation should be added back to nfsd_file_fsync() > or its callers. It might give more useful warnings if you were to > annotate the external API functions (as was done here) rather than > internal helper functions. > Actually, it's probably better in nfsd_file_put(). That'll give us more coverage. > > > - > > - if (test_bit(NFSD_FILE_GC, &nf->nf_flags)) > > - nfsd_file_lru_add(nf); > > - else if (refcount_read(&nf->nf_ref) == 2) > > - nfsd_file_unhash_and_put(nf); > > - > > - if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > > - nfsd_file_fsync(nf); > > - nfsd_file_put_noref(nf); > > - } else if (nf->nf_file && test_bit(NFSD_FILE_GC, &nf->nf_flags)) { > > - nfsd_file_put_noref(nf); > > - nfsd_file_schedule_laundrette(); > > This might be the only caller of nfsd_file_schedule_laundrette. > How does the laundrette get scheduled now? > Good point. I think we need to schedule it any time an entry is added to the LRU. > > - } else > > - nfsd_file_put_noref(nf); > > -} > > - > > -static void > > -nfsd_file_dispose_list(struct list_head *dispose) > > -{ > > - struct nfsd_file *nf; > > + trace_nfsd_file_put(nf); > > > > - while(!list_empty(dispose)) { > > - nf = list_first_entry(dispose, struct nfsd_file, nf_lru); > > - list_del_init(&nf->nf_lru); > > - nfsd_file_fsync(nf); > > - nfsd_file_put_noref(nf); > > + /* > > + * The HASHED check is racy. We may end up with the occasional > > + * unhashed entry on the LRU, but they should get cleaned up > > + * like any other. > > + */ > > + if (test_bit(NFSD_FILE_GC, &nf->nf_flags) && > > + test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > > + /* > > + * If this is the last reference (nf_ref == 1), then transfer > > + * it to the LRU. If the add to the LRU fails, just put it as > > + * usual. > > + */ > > + if (refcount_dec_not_one(&nf->nf_ref) || nfsd_file_lru_add(nf)) > > + return; > > } > > + if (refcount_dec_and_test(&nf->nf_ref)) > > + nfsd_file_free(nf); > > } > > > > static void > > -nfsd_file_dispose_list_sync(struct list_head *dispose) > > +nfsd_file_dispose_list(struct list_head *dispose) > > { > > - bool flush = false; > > struct nfsd_file *nf; > > > > while(!list_empty(dispose)) { > > nf = list_first_entry(dispose, struct nfsd_file, nf_lru); > > list_del_init(&nf->nf_lru); > > - nfsd_file_fsync(nf); > > - if (!refcount_dec_and_test(&nf->nf_ref)) > > - continue; > > - if (nfsd_file_free(nf)) > > - flush = true; > > + nfsd_file_free(nf); > > } > > - if (flush) > > - flush_delayed_fput(); > > } > > > > static void > > @@ -564,21 +567,8 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > > struct list_head *head = arg; > > struct nfsd_file *nf = list_entry(item, struct nfsd_file, nf_lru); > > > > - /* > > - * Do a lockless refcount check. The hashtable holds one reference, so > > - * we look to see if anything else has a reference, or if any have > > - * been put since the shrinker last ran. Those don't get unhashed and > > - * released. > > - * > > - * Note that in the put path, we set the flag and then decrement the > > - * counter. Here we check the counter and then test and clear the flag. > > - * That order is deliberate to ensure that we can do this locklessly. > > - */ > > - if (refcount_read(&nf->nf_ref) > 1) { > > - list_lru_isolate(lru, &nf->nf_lru); > > - trace_nfsd_file_gc_in_use(nf); > > - return LRU_REMOVED; > > - } > > + /* We should only be dealing with v2/3 entries here */ > > + WARN_ON_ONCE(!test_bit(NFSD_FILE_GC, &nf->nf_flags)); > > > > /* > > * Don't throw out files that are still undergoing I/O or > > @@ -589,40 +579,30 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, > > return LRU_SKIP; > > } > > > > + /* If it was recently added to the list, skip it */ > > if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags)) { > > trace_nfsd_file_gc_referenced(nf); > > return LRU_ROTATE; > > } > > > > - if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > > - trace_nfsd_file_gc_hashed(nf); > > - return LRU_SKIP; > > + /* > > + * Put the reference held on behalf of the LRU. If it wasn't the last > > + * one, then just remove it from the LRU and ignore it. > > + */ > > + if (!refcount_dec_and_test(&nf->nf_ref)) { > > + trace_nfsd_file_gc_in_use(nf); > > + list_lru_isolate(lru, &nf->nf_lru); > > + return LRU_REMOVED; > > } > > > > + /* Refcount went to zero. Unhash it and queue it to the dispose list */ > > + nfsd_file_unhash(nf); > > list_lru_isolate_move(lru, &nf->nf_lru, head); > > this_cpu_inc(nfsd_file_evictions); > > trace_nfsd_file_gc_disposed(nf); > > return LRU_REMOVED; > > } > > > > -/* > > - * Unhash items on @dispose immediately, then queue them on the > > - * disposal workqueue to finish releasing them in the background. > > - * > > - * cel: Note that between the time list_lru_shrink_walk runs and > > - * now, these items are in the hash table but marked unhashed. > > - * Why release these outside of lru_cb ? There's no lock ordering > > - * problem since lru_cb currently takes no lock. > > - */ > > -static void nfsd_file_gc_dispose_list(struct list_head *dispose) > > -{ > > - struct nfsd_file *nf; > > - > > - list_for_each_entry(nf, dispose, nf_lru) > > - nfsd_file_hash_remove(nf); > > - nfsd_file_dispose_list_delayed(dispose); > > -} > > - > > static void > > nfsd_file_gc(void) > > { > > @@ -632,7 +612,7 @@ nfsd_file_gc(void) > > ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb, > > &dispose, list_lru_count(&nfsd_file_lru)); > > trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru)); > > - nfsd_file_gc_dispose_list(&dispose); > > + nfsd_file_dispose_list_delayed(&dispose); > > } > > > > static void > > @@ -657,7 +637,7 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc) > > ret = list_lru_shrink_walk(&nfsd_file_lru, sc, > > nfsd_file_lru_cb, &dispose); > > trace_nfsd_file_shrinker_removed(ret, list_lru_count(&nfsd_file_lru)); > > - nfsd_file_gc_dispose_list(&dispose); > > + nfsd_file_dispose_list_delayed(&dispose); > > return ret; > > } > > > > @@ -668,8 +648,11 @@ static struct shrinker nfsd_file_shrinker = { > > }; > > > > /* > > - * Find all cache items across all net namespaces that match @inode and > > - * move them to @dispose. The lookup is atomic wrt nfsd_file_acquire(). > > + * Find all cache items across all net namespaces that match @inode, unhash > > + * them, take references and then put them on @dispose if that was successful. > > + * > > + * The nfsd_file objects on the list will be unhashed, and each will have a > > + * reference taken. > > */ > > static unsigned int > > __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > > @@ -687,8 +670,9 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > > nfsd_file_rhash_params); > > if (!nf) > > break; > > - nfsd_file_unhash_and_queue(nf, dispose); > > - count++; > > + > > + if (nfsd_file_unhash_and_queue(nf, dispose)) > > + count++; > > } while (1); > > rcu_read_unlock(); > > return count; > > @@ -700,15 +684,25 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) > > * > > * Unhash and put all cache item associated with @inode. > > */ > > -static void > > +static unsigned int > > nfsd_file_close_inode(struct inode *inode) > > { > > - LIST_HEAD(dispose); > > + struct nfsd_file *nf; > > unsigned int count; > > + LIST_HEAD(dispose); > > > > count = __nfsd_file_close_inode(inode, &dispose); > > trace_nfsd_file_close_inode(inode, count); > > - nfsd_file_dispose_list_delayed(&dispose); > > + if (count) { > > Why is it necessary to check @count? I would think that > the the empty list check would be sufficient. > > It's not necessary. I'll change it. > > + while(!list_empty(&dispose)) { > > + nf = list_first_entry(&dispose, struct nfsd_file, nf_lru); > > + list_del_init(&nf->nf_lru); > > + trace_nfsd_file_closing(nf); > > + if (refcount_dec_and_test(&nf->nf_ref)) > > + nfsd_file_free(nf); > > + } > > + } > > + return count; > > } > > > > /** > > @@ -720,19 +714,15 @@ nfsd_file_close_inode(struct inode *inode) > > void > > nfsd_file_close_inode_sync(struct inode *inode) > > { > > - LIST_HEAD(dispose); > > - unsigned int count; > > - > > - count = __nfsd_file_close_inode(inode, &dispose); > > - trace_nfsd_file_close_inode_sync(inode, count); > > - nfsd_file_dispose_list_sync(&dispose); > > + if (nfsd_file_close_inode(inode)) > > + flush_delayed_fput(); > > } > > > > /** > > * nfsd_file_delayed_close - close unused nfsd_files > > * @work: dummy > > * > > - * Walk the LRU list and close any entries that have not been used since > > + * Walk the LRU list and destroy any entries that have not been used since > > * the last scan. > > */ > > static void > > @@ -1054,8 +1044,10 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > > rcu_read_lock(); > > nf = rhashtable_lookup(&nfsd_file_rhash_tbl, &key, > > nfsd_file_rhash_params); > > - if (nf) > > - nf = nfsd_file_get(nf); > > + if (nf) { > > + if (!nfsd_file_lru_remove(nf)) > > + nf = nfsd_file_get(nf); > > + } > > rcu_read_unlock(); > > if (nf) > > goto wait_for_construction; > > @@ -1090,11 +1082,11 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > > goto out; > > } > > open_retry = false; > > - nfsd_file_put_noref(nf); > > + if (refcount_dec_and_test(&nf->nf_ref)) > > + nfsd_file_free(nf); > > goto retry; > > } > > > > - nfsd_file_lru_remove(nf); > > this_cpu_inc(nfsd_file_cache_hits); > > > > status = nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_flags)); > > @@ -1104,7 +1096,8 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > > this_cpu_inc(nfsd_file_acquisitions); > > *pnf = nf; > > } else { > > - nfsd_file_put(nf); > > + if (refcount_dec_and_test(&nf->nf_ref)) > > + nfsd_file_free(nf); > > nf = NULL; > > } > > > > @@ -1131,7 +1124,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, > > * then unhash. > > */ > > if (status != nfs_ok || key.inode->i_nlink == 0) > > - nfsd_file_unhash_and_put(nf); > > + nfsd_file_unhash(nf); > > clear_bit_unlock(NFSD_FILE_PENDING, &nf->nf_flags); > > smp_mb__after_atomic(); > > wake_up_bit(&nf->nf_flags, NFSD_FILE_PENDING); > > diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h > > index 940252482fd4..a44ded06af87 100644 > > --- a/fs/nfsd/trace.h > > +++ b/fs/nfsd/trace.h > > @@ -906,6 +906,7 @@ DEFINE_EVENT(nfsd_file_class, name, \ > > DEFINE_NFSD_FILE_EVENT(nfsd_file_free); > > DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash); > > DEFINE_NFSD_FILE_EVENT(nfsd_file_put); > > +DEFINE_NFSD_FILE_EVENT(nfsd_file_closing); > > DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash_and_queue); > > > > TRACE_EVENT(nfsd_file_alloc, > > -- > > 2.38.1 > > Thanks again for the review!
diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index ce80b6a80ffc..d928c5e38eeb 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -1,6 +1,12 @@ // SPDX-License-Identifier: GPL-2.0 /* * The NFSD open file cache. + * + * Each nfsd_file is created in response to client activity -- either regular + * file I/O for v2/v3, or opening a file for v4. Files opened via v4 are + * cleaned up as soon as their refcount goes to 0. Entries for v2/v3 are + * flagged with NFSD_FILE_GC. On their last put, they are added to the LRU for + * eventual disposal if they aren't used again within a short time period. */ #include <linux/hash.h> @@ -301,8 +307,7 @@ nfsd_file_alloc(struct nfsd_file_lookup_key *key, unsigned int may) if (key->gc) __set_bit(NFSD_FILE_GC, &nf->nf_flags); nf->nf_inode = key->inode; - /* nf_ref is pre-incremented for hash table */ - refcount_set(&nf->nf_ref, 2); + refcount_set(&nf->nf_ref, 1); nf->nf_may = key->need; nf->nf_mark = NULL; } @@ -351,23 +356,25 @@ nfsd_file_unhash(struct nfsd_file *nf) return false; } -static bool +static void nfsd_file_free(struct nfsd_file *nf) { s64 age = ktime_to_ms(ktime_sub(ktime_get(), nf->nf_birthtime)); - bool flush = false; + + trace_nfsd_file_free(nf); this_cpu_inc(nfsd_file_releases); this_cpu_add(nfsd_file_total_age, age); - trace_nfsd_file_free(nf); + nfsd_file_unhash(nf); + nfsd_file_fsync(nf); + if (nf->nf_mark) nfsd_file_mark_put(nf->nf_mark); if (nf->nf_file) { get_file(nf->nf_file); filp_close(nf->nf_file, NULL); fput(nf->nf_file); - flush = true; } /* @@ -375,10 +382,9 @@ nfsd_file_free(struct nfsd_file *nf) * WARN and leak it to preserve system stability. */ if (WARN_ON_ONCE(!list_empty(&nf->nf_lru))) - return flush; + return; call_rcu(&nf->nf_rcu, nfsd_file_slab_free); - return flush; } static bool @@ -394,17 +400,23 @@ nfsd_file_check_writeback(struct nfsd_file *nf) mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK); } -static void nfsd_file_lru_add(struct nfsd_file *nf) +static bool nfsd_file_lru_add(struct nfsd_file *nf) { set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); - if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) + if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_add(nf); + return true; + } + return false; } -static void nfsd_file_lru_remove(struct nfsd_file *nf) +static bool nfsd_file_lru_remove(struct nfsd_file *nf) { - if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) + if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_del(nf); + return true; + } + return false; } struct nfsd_file * @@ -415,86 +427,77 @@ nfsd_file_get(struct nfsd_file *nf) return NULL; } -static void +/** + * nfsd_file_unhash_and_queue - unhash a file and queue it to the dispose list + * @nf: nfsd_file to be unhashed and queued + * @dispose: list to which it should be queued + * + * Attempt to unhash a nfsd_file and queue it to the given list. Each file + * will have a reference held on behalf of the list. That reference may come + * from the LRU, or we may need to take one. If we can't get a reference, + * ignore it altogether. + */ +static bool nfsd_file_unhash_and_queue(struct nfsd_file *nf, struct list_head *dispose) { trace_nfsd_file_unhash_and_queue(nf); if (nfsd_file_unhash(nf)) { - /* caller must call nfsd_file_dispose_list() later */ - nfsd_file_lru_remove(nf); + /* + * If we remove it from the LRU, then just use that + * reference for the dispose list. Otherwise, we need + * to take a reference. If that fails, just ignore + * the file altogether. + */ + if (!nfsd_file_lru_remove(nf) && !nfsd_file_get(nf)) + return false; list_add(&nf->nf_lru, dispose); + return true; } + return false; } -static void -nfsd_file_put_noref(struct nfsd_file *nf) -{ - trace_nfsd_file_put(nf); - - if (refcount_dec_and_test(&nf->nf_ref)) { - WARN_ON(test_bit(NFSD_FILE_HASHED, &nf->nf_flags)); - nfsd_file_lru_remove(nf); - nfsd_file_free(nf); - } -} - -static void -nfsd_file_unhash_and_put(struct nfsd_file *nf) -{ - if (nfsd_file_unhash(nf)) - nfsd_file_put_noref(nf); -} - +/** + * nfsd_file_put - put the reference to a nfsd_file + * @nf: nfsd_file of which to put the reference + * + * Put a reference to a nfsd_file. In the v4 case, we just put the + * reference immediately. In the v2/3 case, if the reference would be + * the last one, the put it on the LRU instead to be cleaned up later. + */ void nfsd_file_put(struct nfsd_file *nf) { - might_sleep(); - - if (test_bit(NFSD_FILE_GC, &nf->nf_flags)) - nfsd_file_lru_add(nf); - else if (refcount_read(&nf->nf_ref) == 2) - nfsd_file_unhash_and_put(nf); - - if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { - nfsd_file_fsync(nf); - nfsd_file_put_noref(nf); - } else if (nf->nf_file && test_bit(NFSD_FILE_GC, &nf->nf_flags)) { - nfsd_file_put_noref(nf); - nfsd_file_schedule_laundrette(); - } else - nfsd_file_put_noref(nf); -} - -static void -nfsd_file_dispose_list(struct list_head *dispose) -{ - struct nfsd_file *nf; + trace_nfsd_file_put(nf); - while(!list_empty(dispose)) { - nf = list_first_entry(dispose, struct nfsd_file, nf_lru); - list_del_init(&nf->nf_lru); - nfsd_file_fsync(nf); - nfsd_file_put_noref(nf); + /* + * The HASHED check is racy. We may end up with the occasional + * unhashed entry on the LRU, but they should get cleaned up + * like any other. + */ + if (test_bit(NFSD_FILE_GC, &nf->nf_flags) && + test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { + /* + * If this is the last reference (nf_ref == 1), then transfer + * it to the LRU. If the add to the LRU fails, just put it as + * usual. + */ + if (refcount_dec_not_one(&nf->nf_ref) || nfsd_file_lru_add(nf)) + return; } + if (refcount_dec_and_test(&nf->nf_ref)) + nfsd_file_free(nf); } static void -nfsd_file_dispose_list_sync(struct list_head *dispose) +nfsd_file_dispose_list(struct list_head *dispose) { - bool flush = false; struct nfsd_file *nf; while(!list_empty(dispose)) { nf = list_first_entry(dispose, struct nfsd_file, nf_lru); list_del_init(&nf->nf_lru); - nfsd_file_fsync(nf); - if (!refcount_dec_and_test(&nf->nf_ref)) - continue; - if (nfsd_file_free(nf)) - flush = true; + nfsd_file_free(nf); } - if (flush) - flush_delayed_fput(); } static void @@ -564,21 +567,8 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, struct list_head *head = arg; struct nfsd_file *nf = list_entry(item, struct nfsd_file, nf_lru); - /* - * Do a lockless refcount check. The hashtable holds one reference, so - * we look to see if anything else has a reference, or if any have - * been put since the shrinker last ran. Those don't get unhashed and - * released. - * - * Note that in the put path, we set the flag and then decrement the - * counter. Here we check the counter and then test and clear the flag. - * That order is deliberate to ensure that we can do this locklessly. - */ - if (refcount_read(&nf->nf_ref) > 1) { - list_lru_isolate(lru, &nf->nf_lru); - trace_nfsd_file_gc_in_use(nf); - return LRU_REMOVED; - } + /* We should only be dealing with v2/3 entries here */ + WARN_ON_ONCE(!test_bit(NFSD_FILE_GC, &nf->nf_flags)); /* * Don't throw out files that are still undergoing I/O or @@ -589,40 +579,30 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru, return LRU_SKIP; } + /* If it was recently added to the list, skip it */ if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags)) { trace_nfsd_file_gc_referenced(nf); return LRU_ROTATE; } - if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { - trace_nfsd_file_gc_hashed(nf); - return LRU_SKIP; + /* + * Put the reference held on behalf of the LRU. If it wasn't the last + * one, then just remove it from the LRU and ignore it. + */ + if (!refcount_dec_and_test(&nf->nf_ref)) { + trace_nfsd_file_gc_in_use(nf); + list_lru_isolate(lru, &nf->nf_lru); + return LRU_REMOVED; } + /* Refcount went to zero. Unhash it and queue it to the dispose list */ + nfsd_file_unhash(nf); list_lru_isolate_move(lru, &nf->nf_lru, head); this_cpu_inc(nfsd_file_evictions); trace_nfsd_file_gc_disposed(nf); return LRU_REMOVED; } -/* - * Unhash items on @dispose immediately, then queue them on the - * disposal workqueue to finish releasing them in the background. - * - * cel: Note that between the time list_lru_shrink_walk runs and - * now, these items are in the hash table but marked unhashed. - * Why release these outside of lru_cb ? There's no lock ordering - * problem since lru_cb currently takes no lock. - */ -static void nfsd_file_gc_dispose_list(struct list_head *dispose) -{ - struct nfsd_file *nf; - - list_for_each_entry(nf, dispose, nf_lru) - nfsd_file_hash_remove(nf); - nfsd_file_dispose_list_delayed(dispose); -} - static void nfsd_file_gc(void) { @@ -632,7 +612,7 @@ nfsd_file_gc(void) ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb, &dispose, list_lru_count(&nfsd_file_lru)); trace_nfsd_file_gc_removed(ret, list_lru_count(&nfsd_file_lru)); - nfsd_file_gc_dispose_list(&dispose); + nfsd_file_dispose_list_delayed(&dispose); } static void @@ -657,7 +637,7 @@ nfsd_file_lru_scan(struct shrinker *s, struct shrink_control *sc) ret = list_lru_shrink_walk(&nfsd_file_lru, sc, nfsd_file_lru_cb, &dispose); trace_nfsd_file_shrinker_removed(ret, list_lru_count(&nfsd_file_lru)); - nfsd_file_gc_dispose_list(&dispose); + nfsd_file_dispose_list_delayed(&dispose); return ret; } @@ -668,8 +648,11 @@ static struct shrinker nfsd_file_shrinker = { }; /* - * Find all cache items across all net namespaces that match @inode and - * move them to @dispose. The lookup is atomic wrt nfsd_file_acquire(). + * Find all cache items across all net namespaces that match @inode, unhash + * them, take references and then put them on @dispose if that was successful. + * + * The nfsd_file objects on the list will be unhashed, and each will have a + * reference taken. */ static unsigned int __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) @@ -687,8 +670,9 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) nfsd_file_rhash_params); if (!nf) break; - nfsd_file_unhash_and_queue(nf, dispose); - count++; + + if (nfsd_file_unhash_and_queue(nf, dispose)) + count++; } while (1); rcu_read_unlock(); return count; @@ -700,15 +684,25 @@ __nfsd_file_close_inode(struct inode *inode, struct list_head *dispose) * * Unhash and put all cache item associated with @inode. */ -static void +static unsigned int nfsd_file_close_inode(struct inode *inode) { - LIST_HEAD(dispose); + struct nfsd_file *nf; unsigned int count; + LIST_HEAD(dispose); count = __nfsd_file_close_inode(inode, &dispose); trace_nfsd_file_close_inode(inode, count); - nfsd_file_dispose_list_delayed(&dispose); + if (count) { + while(!list_empty(&dispose)) { + nf = list_first_entry(&dispose, struct nfsd_file, nf_lru); + list_del_init(&nf->nf_lru); + trace_nfsd_file_closing(nf); + if (refcount_dec_and_test(&nf->nf_ref)) + nfsd_file_free(nf); + } + } + return count; } /** @@ -720,19 +714,15 @@ nfsd_file_close_inode(struct inode *inode) void nfsd_file_close_inode_sync(struct inode *inode) { - LIST_HEAD(dispose); - unsigned int count; - - count = __nfsd_file_close_inode(inode, &dispose); - trace_nfsd_file_close_inode_sync(inode, count); - nfsd_file_dispose_list_sync(&dispose); + if (nfsd_file_close_inode(inode)) + flush_delayed_fput(); } /** * nfsd_file_delayed_close - close unused nfsd_files * @work: dummy * - * Walk the LRU list and close any entries that have not been used since + * Walk the LRU list and destroy any entries that have not been used since * the last scan. */ static void @@ -1054,8 +1044,10 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, rcu_read_lock(); nf = rhashtable_lookup(&nfsd_file_rhash_tbl, &key, nfsd_file_rhash_params); - if (nf) - nf = nfsd_file_get(nf); + if (nf) { + if (!nfsd_file_lru_remove(nf)) + nf = nfsd_file_get(nf); + } rcu_read_unlock(); if (nf) goto wait_for_construction; @@ -1090,11 +1082,11 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, goto out; } open_retry = false; - nfsd_file_put_noref(nf); + if (refcount_dec_and_test(&nf->nf_ref)) + nfsd_file_free(nf); goto retry; } - nfsd_file_lru_remove(nf); this_cpu_inc(nfsd_file_cache_hits); status = nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_flags)); @@ -1104,7 +1096,8 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, this_cpu_inc(nfsd_file_acquisitions); *pnf = nf; } else { - nfsd_file_put(nf); + if (refcount_dec_and_test(&nf->nf_ref)) + nfsd_file_free(nf); nf = NULL; } @@ -1131,7 +1124,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp, * then unhash. */ if (status != nfs_ok || key.inode->i_nlink == 0) - nfsd_file_unhash_and_put(nf); + nfsd_file_unhash(nf); clear_bit_unlock(NFSD_FILE_PENDING, &nf->nf_flags); smp_mb__after_atomic(); wake_up_bit(&nf->nf_flags, NFSD_FILE_PENDING); diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h index 940252482fd4..a44ded06af87 100644 --- a/fs/nfsd/trace.h +++ b/fs/nfsd/trace.h @@ -906,6 +906,7 @@ DEFINE_EVENT(nfsd_file_class, name, \ DEFINE_NFSD_FILE_EVENT(nfsd_file_free); DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash); DEFINE_NFSD_FILE_EVENT(nfsd_file_put); +DEFINE_NFSD_FILE_EVENT(nfsd_file_closing); DEFINE_NFSD_FILE_EVENT(nfsd_file_unhash_and_queue); TRACE_EVENT(nfsd_file_alloc,
The filecache refcounting is a bit non-standard for something searchable by RCU, in that we maintain a sentinel reference while it's hashed. This in turn requires that we have to do things differently in the "put" depending on whether its hashed, which we believe to have led to races. There are other problems in here too. nfsd_file_close_inode_sync can end up freeing an nfsd_file while there are still outstanding references to it, and there are a number of subtle ToC/ToU races. Rework the code so that the refcount is what drives the lifecycle. When the refcount goes to zero, then unhash and rcu free the object. With this change, the LRU carries a reference. Take special care to deal with it when removing an entry from the list. Signed-off-by: Jeff Layton <jlayton@kernel.org> --- fs/nfsd/filecache.c | 247 +++++++++++++++++++++----------------------- fs/nfsd/trace.h | 1 + 2 files changed, 121 insertions(+), 127 deletions(-)