The patch titled
Subject: z3fold: fix potential race in z3fold_reclaim_page
has been added to the -mm tree. Its filename is
z3fold-fix-potential-race-in-z3fold_reclaim_page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/z3fold-fix-potential-race-in-z3fold_reclaim_page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/z3fold-fix-potential-race-in-z3fold_reclaim_page.patch
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------------------------------------------------------
From: Vitaly Wool <vitalywool@xxxxxxxxx>
Subject: 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@xxxxxxxxx
Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: <Oleksiy.Avramchenko@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/z3fold.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff -puN mm/z3fold.c~z3fold-fix-potential-race-in-z3fold_reclaim_page mm/z3fold.c
--- a/mm/z3fold.c~z3fold-fix-potential-race-in-z3fold_reclaim_page
+++ a/mm/z3fold.c
@@ -875,16 +875,18 @@ static int z3fold_reclaim_page(struct z3
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.
_
Patches currently in -mm which might be from vitalywool@xxxxxxxxx are
z3fold-fix-potential-race-in-z3fold_reclaim_page.patch
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