Commit d5567c9d authored Oct 03, 2017 by Vitaly Wool Committed by Linus Torvalds Oct 03, 2017

z3fold: fix potential race in z3fold_reclaim_page

It is possible that on a (partially) unsuccessful page reclaim,
kref_put() called in z3fold_reclaim_page() does not yield page release,
but the page is released shortly afterwards by another thread.  Then
z3fold_reclaim_page() would try to list_add() that (released) page again
which is obviously a bug.

To avoid that, spin_lock() has to be taken earlier, before the
kref_put() call mentioned earlier.

Link: http://lkml.kernel.org/r/20170913162937.bfff21c7d12b12a5f47639fd@gmail.com


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>

parent d9d73e81

mm/z3fold.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -875,16 +875,18 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
		goto next;
		}
		next:
		spin_lock(&pool->lock);
		if (test_bit(PAGE_HEADLESS, &page->private)) {
		if (ret == 0) {
		spin_unlock(&pool->lock);
		free_z3fold_page(page);
		return 0;
		}
		} else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
		atomic64_dec(&pool->pages_nr);
		spin_unlock(&pool->lock);
		return 0;
		}
		spin_lock(&pool->lock);

		/*
		* Add to the beginning of LRU.