| Message ID | 20150820122359.GB12432@techsingularity.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 08/20/2015 02:23 PM, Mel Gorman wrote: > On Mon, Jul 27, 2015 at 01:25:47PM +0200, Jerome Marchand wrote: >> On 07/27/2015 12:52 PM, Mel Gorman wrote: >>> On Wed, Jul 22, 2015 at 03:46:16PM +0200, Jerome Marchand wrote: >>>> On 07/22/2015 02:23 PM, Trond Myklebust wrote: >>>>> On Wed, Jul 22, 2015 at 4:10 AM, Jerome Marchand <jmarchan@redhat.com> wrote: >>>>>> >>>>>> Lockdep warns about a inconsistent {RECLAIM_FS-ON-W} -> >>>>>> {IN-RECLAIM_FS-W} usage. The culpritt is the inode->i_mutex taken in >>>>>> nfs_file_direct_write(). This code was introduced by commit a9ab5e840669 >>>>>> ("nfs: page cache invalidation for dio"). >>>>>> This naive test patch avoid to take the mutex on a swapfile and makes >>>>>> lockdep happy again. However I don't know much about NFS code and I >>>>>> assume it's probably not the proper solution. Any thought? >>>>>> >>>>>> Signed-off-by: Jerome Marchand <jmarchan@redhat.com> >>>>> >>>>> NFS is not the only O_DIRECT implementation to set the inode->i_mutex. >>>>> Why can't this be fixed in the generic swap code instead of adding >>>>> yet-another-exception-for-IS_SWAPFILE? >>>> >>>> I meant to cc Mel. Just added him. >>>> >>> >>> Can the full lockdep warning be included as it'll be easier to see then if >>> the generic swap code can somehow special case this? Currently, generic >>> swapping does not not need to care about how the filesystem locked. >>> For most filesystems, it's writing directly to the blocks on disk and >>> bypassing the FS. In the NFS case it'd be surprising to find that there >>> also are dirty pages in page cache that belong to the swap file as it's >>> going to cause corruption. If there is any special casing it would to only >>> attempt the invalidation in the !swap case and warn if mapping->nrpages. It >>> still would look a bit weird but safer than just not acquiring the mutex >>> and then potentially attempting an invalidation. >>> >> >> [ 6819.501009] ================================= >> [ 6819.501009] [ INFO: inconsistent lock state ] >> [ 6819.501009] 4.2.0-rc1-shmacct-babka-v2-next-20150709+ #255 Not tainted >> [ 6819.501009] --------------------------------- > > Thanks. Sorry for the long delay but I finally got back to the bug this > week. NFS can be modified to special case the swapfile but I was not happy > with the result for multiple reasons. It took me a while to see a way for > the core VM to deal with it. What do you think of the following > approach? Seems sound to me. > More importantly, does it work for you? Yes. > > ---8<--- > nfs: Use swap_lock to prevent parallel swapon activations > > Jerome Marchand reported a lockdep warning as follows > > [ 6819.501009] ================================= > [ 6819.501009] [ INFO: inconsistent lock state ] > [ 6819.501009] 4.2.0-rc1-shmacct-babka-v2-next-20150709+ #255 Not tainted > [ 6819.501009] --------------------------------- > [ 6819.501009] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage. > [ 6819.501009] kswapd0/38 [HC0[0]:SC0[0]:HE1:SE1] takes: > [ 6819.501009] (&sb->s_type->i_mutex_key#17){+.+.?.}, at: [<ffffffffa03772a5>] nfs_file_direct_write+0x85/0x3f0 [nfs] > [ 6819.501009] {RECLAIM_FS-ON-W} state was registered at: > [ 6819.501009] [<ffffffff81107f51>] mark_held_locks+0x71/0x90 > [ 6819.501009] [<ffffffff8110b775>] lockdep_trace_alloc+0x75/0xe0 > [ 6819.501009] [<ffffffff81245529>] kmem_cache_alloc_node_trace+0x39/0x440 > [ 6819.501009] [<ffffffff81225b8f>] __get_vm_area_node+0x7f/0x160 > [ 6819.501009] [<ffffffff81226eb2>] __vmalloc_node_range+0x72/0x2c0 > [ 6819.501009] [<ffffffff81227424>] vzalloc+0x54/0x60 > [ 6819.501009] [<ffffffff8122c7c8>] SyS_swapon+0x628/0xfc0 > [ 6819.501009] [<ffffffff81867772>] entry_SYSCALL_64_fastpath+0x12/0x76 > > It's due to NFS acquiring i_mutex since a9ab5e840669 ("nfs: page > cache invalidation for dio") to invalidate page cache before direct I/O. > Filesystems may safely acquire i_mutex during direct writes but NFS is unique > in its treatment of swap files. Ordinarily swap files are supported by the > core VM looking up the physical block for a given offset in advance. There > is no physical block for NFS and the direct write paths are used after > calling mapping->swap_activate. > > The lockdep warning is triggered by swapon(), which is not in reclaim > context, acquiring the i_mutex to ensure a swapfile is not activated twice. > > swapon does not need the i_mutex for this purpose. There is a requirement > that fallocate not be used on swapfiles but this is protected by the inode > flag S_SWAPFILE and nothing to do with i_mutex. In fact, the current > protection does nothing for block devices. This patch expands the role > of swap_lock to protect against parallel activations of block devices and > swapfiles and removes the use of i_mutex. This both improves the protection > for swapon and avoids the lockdep warning. > > Reported-by: Jerome Marchand <jmarchan@redhat.com> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Tested-by: Jerome Marchand <jmarchan@redhat.com> Thanks, Jerome > --- > mm/swapfile.c | 16 +++++++--------- > 1 file changed, 7 insertions(+), 9 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 41e4581af7c5..d58ed6833fa3 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1928,9 +1928,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) > set_blocksize(bdev, old_block_size); > blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); > } else { > - mutex_lock(&inode->i_mutex); > + spin_lock(&swap_lock); > inode->i_flags &= ~S_SWAPFILE; > - mutex_unlock(&inode->i_mutex); > + spin_unlock(&swap_lock); > } > filp_close(swap_file, NULL); > > @@ -2156,7 +2156,6 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode) > p->flags |= SWP_BLKDEV; > } else if (S_ISREG(inode->i_mode)) { > p->bdev = inode->i_sb->s_bdev; > - mutex_lock(&inode->i_mutex); > if (IS_SWAPFILE(inode)) > return -EBUSY; > } else > @@ -2386,6 +2385,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > goto bad_swap; > } > > + /* prevent parallel swapons */ > + spin_lock(&swap_lock); > p->swap_file = swap_file; > mapping = swap_file->f_mapping; > > @@ -2396,13 +2397,14 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > continue; > if (mapping == q->swap_file->f_mapping) { > error = -EBUSY; > + spin_unlock(&swap_lock); > goto bad_swap; > } > } > > inode = mapping->host; > - /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */ > error = claim_swapfile(p, inode); > + spin_unlock(&swap_lock); > if (unlikely(error)) > goto bad_swap; > > @@ -2543,10 +2545,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > vfree(swap_map); > vfree(cluster_info); > if (swap_file) { > - if (inode && S_ISREG(inode->i_mode)) { > - mutex_unlock(&inode->i_mutex); > + if (inode && S_ISREG(inode->i_mode)) > inode = NULL; > - } > filp_close(swap_file, NULL); > } > out: > @@ -2556,8 +2556,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > } > if (name) > putname(name); > - if (inode && S_ISREG(inode->i_mode)) > - mutex_unlock(&inode->i_mutex); > return error; > } > >
On Tue, Sep 01, 2015 at 06:22:14PM +0200, Jerome Marchand wrote: > > Thanks. Sorry for the long delay but I finally got back to the bug this > > week. NFS can be modified to special case the swapfile but I was not happy > > with the result for multiple reasons. It took me a while to see a way for > > the core VM to deal with it. What do you think of the following > > approach? > > Seems sound to me. > > > More importantly, does it work for you? > > Yes. > Sweet, thanks. It's the merge window now so it won't get fixed now and I know there is already a collision with the mm merge. I'll rebase and repost after 4.3-rc1 comes out.
diff --git a/mm/swapfile.c b/mm/swapfile.c index 41e4581af7c5..d58ed6833fa3 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1928,9 +1928,9 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) set_blocksize(bdev, old_block_size); blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL); } else { - mutex_lock(&inode->i_mutex); + spin_lock(&swap_lock); inode->i_flags &= ~S_SWAPFILE; - mutex_unlock(&inode->i_mutex); + spin_unlock(&swap_lock); } filp_close(swap_file, NULL); @@ -2156,7 +2156,6 @@ static int claim_swapfile(struct swap_info_struct *p, struct inode *inode) p->flags |= SWP_BLKDEV; } else if (S_ISREG(inode->i_mode)) { p->bdev = inode->i_sb->s_bdev; - mutex_lock(&inode->i_mutex); if (IS_SWAPFILE(inode)) return -EBUSY; } else @@ -2386,6 +2385,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto bad_swap; } + /* prevent parallel swapons */ + spin_lock(&swap_lock); p->swap_file = swap_file; mapping = swap_file->f_mapping; @@ -2396,13 +2397,14 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) continue; if (mapping == q->swap_file->f_mapping) { error = -EBUSY; + spin_unlock(&swap_lock); goto bad_swap; } } inode = mapping->host; - /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */ error = claim_swapfile(p, inode); + spin_unlock(&swap_lock); if (unlikely(error)) goto bad_swap; @@ -2543,10 +2545,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) vfree(swap_map); vfree(cluster_info); if (swap_file) { - if (inode && S_ISREG(inode->i_mode)) { - mutex_unlock(&inode->i_mutex); + if (inode && S_ISREG(inode->i_mode)) inode = NULL; - } filp_close(swap_file, NULL); } out: @@ -2556,8 +2556,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) } if (name) putname(name); - if (inode && S_ISREG(inode->i_mode)) - mutex_unlock(&inode->i_mutex); return error; }