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authorVitaly Wool <vitalywool@gmail.com>2017-04-13 14:56:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-04-13 18:24:20 -0700
commit76e32a2a084ed71b48179023cd8fdb3787c8a6ad (patch)
treed0a2cb8e6addcbdcb946192f27243eef0bb7ee3c
parent2760078203a6b46b96307f4b06030ab0b801c97e (diff)
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.c9
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)