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| author | Vitaly Wool <vitalywool@gmail.com> | 2017-04-13 14:56:14 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-04-13 18:24:20 -0700 |
| commit | 76e32a2a084ed71b48179023cd8fdb3787c8a6ad (patch) | |
| tree | d0a2cb8e6addcbdcb946192f27243eef0bb7ee3c | |
| parent | 2760078203a6b46b96307f4b06030ab0b801c97e (diff) | |
| download | lwn-76e32a2a084ed71b48179023cd8fdb3787c8a6ad.tar.gz lwn-76e32a2a084ed71b48179023cd8fdb3787c8a6ad.zip | |
z3fold: fix page locking in z3fold_alloc()
Stress testing of the current z3fold implementation on a 8-core system
revealed it was possible that a z3fold page deleted from its unbuddied
list in z3fold_alloc() would be put on another unbuddied list by
z3fold_free() while z3fold_alloc() is still processing it. This has
been introduced with commit 5a27aa822 ("z3fold: add kref refcounting")
due to the removal of special handling of a z3fold page not on any list
in z3fold_free().
To fix this, the z3fold page lock should be taken in z3fold_alloc()
before the pool lock is released. To avoid deadlocking, we just try to
lock the page as soon as we get a hold of it, and if trylock fails, we
drop this page and take the next one.
Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: <Oleksiy.Avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/z3fold.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/mm/z3fold.c b/mm/z3fold.c index f9492bccfd79..54f63c4a809a 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -185,6 +185,12 @@ static inline void z3fold_page_lock(struct z3fold_header *zhdr) spin_lock(&zhdr->page_lock); } +/* Try to lock a z3fold page */ +static inline int z3fold_page_trylock(struct z3fold_header *zhdr) +{ + return spin_trylock(&zhdr->page_lock); +} + /* Unlock a z3fold page */ static inline void z3fold_page_unlock(struct z3fold_header *zhdr) { @@ -385,7 +391,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, spin_lock(&pool->lock); zhdr = list_first_entry_or_null(&pool->unbuddied[i], struct z3fold_header, buddy); - if (!zhdr) { + if (!zhdr || !z3fold_page_trylock(zhdr)) { spin_unlock(&pool->lock); continue; } @@ -394,7 +400,6 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, spin_unlock(&pool->lock); page = virt_to_page(zhdr); - z3fold_page_lock(zhdr); if (zhdr->first_chunks == 0) { if (zhdr->middle_chunks != 0 && chunks >= zhdr->start_middle) |