| Message ID | 1515454691-69220-1-git-send-email-jiang.biao2@zte.com.cn (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 9 Jan 2018 07:38:11 +0800 Jiang Biao <jiang.biao2@zte.com.cn> wrote: > When running ltp stress test for 7*24 hours, vmscan occasionally emits the > following warning continuously: > > mb_cache_scan+0x0/0x3f0 negative objects to delete > nr=-9232265467809300450 > .... > > Trace info shows the freeable(mb_cache_count returns) is -1, which causes > the continuous accumulation and overflow of total_scan. > > This patch makes sure that mb_cache_count() not return a negative value, > which makes the mbcache shrinker more robust. > > ... > > --- a/fs/mbcache.c > +++ b/fs/mbcache.c > @@ -238,7 +238,11 @@ void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value) > spin_lock(&cache->c_list_lock); > if (!list_empty(&entry->e_list)) { > list_del_init(&entry->e_list); > - cache->c_entry_count--; > + if (cache->c_entry_count > 0) > + cache->c_entry_count--; > + else > + WARN_ONCE(1, "mbcache: Entry count " > + "going negative!\n"); > atomic_dec(&entry->e_refcnt); > } > spin_unlock(&cache->c_list_lock); I agree with Jan's comment. We need to figure out how ->c_entry_count went negative. mb_cache_count() says this state is "Unlikely, but not impossible", but from a quick read I can't see how this happens - it appears that coherency between ->c_list and ->c_entry_count is always maintained under ->c_list_lock?
diff --git a/fs/mbcache.c b/fs/mbcache.c index b8b8b9c..2a800e3 100644 --- a/fs/mbcache.c +++ b/fs/mbcache.c @@ -238,7 +238,11 @@ void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value) spin_lock(&cache->c_list_lock); if (!list_empty(&entry->e_list)) { list_del_init(&entry->e_list); - cache->c_entry_count--; + if (cache->c_entry_count > 0) + cache->c_entry_count--; + else + WARN_ONCE(1, "mbcache: Entry count " + "going negative!\n"); atomic_dec(&entry->e_refcnt); } spin_unlock(&cache->c_list_lock);
When running ltp stress test for 7*24 hours, vmscan occasionally emits the following warning continuously: mb_cache_scan+0x0/0x3f0 negative objects to delete nr=-9232265467809300450 .... Trace info shows the freeable(mb_cache_count returns) is -1, which causes the continuous accumulation and overflow of total_scan. This patch makes sure that mb_cache_count() not return a negative value, which makes the mbcache shrinker more robust. Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn> CC: "Theodore Ts'o" <tytso@mit.edu> CC: Eric Biggers <ebiggers@google.com> CC: Andrew Morton <akpm@linux-foundation.org> CC: Jan Kara <jack@suse.cz> --- fs/mbcache.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)