The patch titled
Subject: z3fold: avoid subtle race when freeing slots
has been added to the -mm tree. Its filename is
z3fold-avoid-subtle-race-when-freeing-slots.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/z3fold-avoid-subtle-race-when-freeing-slots.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/z3fold-avoid-subtle-race-when-freeing-slots.patch
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------------------------------------------------------
From: Vitaly Wool <vitalywool@xxxxxxxxx>
Subject: z3fold: avoid subtle race when freeing slots
There is a subtle race between freeing slots and setting the last slot to
zero since the OPRPHANED flag was set after the rwlock had been released.
Fix that to avoid rare memory leaks caused by this race.
Link: http://lkml.kernel.org/r/20191127152118.6314b99074b0626d4c5a8835@xxxxxxxxx
Signed-off-by: Vitaly Wool <vitaly.vul@xxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Henry Burns <henrywolfeburns@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/z3fold.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
--- a/mm/z3fold.c~z3fold-avoid-subtle-race-when-freeing-slots
+++ a/mm/z3fold.c
@@ -327,6 +327,10 @@ static inline void free_handle(unsigned
zhdr->foreign_handles--;
is_free = true;
read_lock(&slots->lock);
+ if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
+ read_unlock(&slots->lock);
+ return;
+ }
for (i = 0; i <= BUDDY_MASK; i++) {
if (slots->slot[i]) {
is_free = false;
@@ -335,7 +339,7 @@ static inline void free_handle(unsigned
}
read_unlock(&slots->lock);
- if (is_free && test_and_clear_bit(HANDLES_ORPHANED, &slots->pool)) {
+ if (is_free) {
struct z3fold_pool *pool = slots_to_pool(slots);
kmem_cache_free(pool->c_handle, slots);
@@ -531,12 +535,12 @@ static void __release_z3fold_page(struct
break;
}
}
+ if (!is_free)
+ set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
read_unlock(&zhdr->slots->lock);
if (is_free)
kmem_cache_free(pool->c_handle, zhdr->slots);
- else
- set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
if (locked)
z3fold_page_unlock(zhdr);
_
Patches currently in -mm which might be from vitalywool@xxxxxxxxx are
z3fold-avoid-subtle-race-when-freeing-slots.patch
z3fold-compact-objects-more-accurately.patch
z3fold-protect-handle-reads.patch
