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authorVitaly Wool <vitalywool@gmail.com>2017-11-17 15:26:16 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-11-17 16:10:00 -0800
commit5d03a6613957785e94af7a4a6212ad4af66aa5c2 (patch)
tree973176f96aa7dfc154525c1513dc920a2fee912e /mm
parent1334be3657dd02af0591d6d8adf0e6a60a7710a6 (diff)
download96b-common-5d03a6613957785e94af7a4a6212ad4af66aa5c2.tar.gz
mm/z3fold.c: use kref to prevent page free/compact race
There is a race in the current z3fold implementation between do_compact() called in a work queue context and the page release procedure when page's kref goes to 0. do_compact() may be waiting for page lock, which is released by release_z3fold_page_locked right before putting the page onto the "stale" list, and then the page may be freed as do_compact() modifies its contents. The mechanism currently implemented to handle that (checking the PAGE_STALE flag) is not reliable enough. Instead, we'll use page's kref counter to guarantee that the page is not released if its compaction is scheduled. It then becomes compaction function's responsibility to decrease the counter and quit immediately if the page was actually freed. Link: http://lkml.kernel.org/r/20171117092032.00ea56f42affbed19f4fcc6c@gmail.com Signed-off-by: Vitaly Wool <vitaly.wool@sonymobile.com> Cc: <Oleksiy.Avramchenko@sony.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/z3fold.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/mm/z3fold.c b/mm/z3fold.c
index b2ba2ba585f3..39e19125d6a0 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -404,8 +404,7 @@ static void do_compact_page(struct z3fold_header *zhdr, bool locked)
WARN_ON(z3fold_page_trylock(zhdr));
else
z3fold_page_lock(zhdr);
- if (test_bit(PAGE_STALE, &page->private) ||
- !test_and_clear_bit(NEEDS_COMPACTING, &page->private)) {
+ if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
z3fold_page_unlock(zhdr);
return;
}
@@ -413,6 +412,11 @@ static void do_compact_page(struct z3fold_header *zhdr, bool locked)
list_del_init(&zhdr->buddy);
spin_unlock(&pool->lock);
+ if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
+ atomic64_dec(&pool->pages_nr);
+ return;
+ }
+
z3fold_compact_page(zhdr);
unbuddied = get_cpu_ptr(pool->unbuddied);
fchunks = num_free_chunks(zhdr);
@@ -753,9 +757,11 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
list_del_init(&zhdr->buddy);
spin_unlock(&pool->lock);
zhdr->cpu = -1;
+ kref_get(&zhdr->refcount);
do_compact_page(zhdr, true);
return;
}
+ kref_get(&zhdr->refcount);
queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
z3fold_page_unlock(zhdr);
}