From 76e32a2a084ed71b48179023cd8fdb3787c8a6ad Mon Sep 17 00:00:00 2001 From: Vitaly Wool Date: Thu, 13 Apr 2017 14:56:14 -0700 Subject: [PATCH] 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 Cc: Dan Streetman Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/z3fold.c | 9 +++++++-- 1 file 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) -- 2.20.1