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Subject[PATCH 4.10 73/75] kasan: resched in quarantine_remove_cache()
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4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Vyukov <dvyukov@google.com>

commit 68fd814a3391c7e017ae6ace8855788748edd981 upstream.

We see reported stalls/lockups in quarantine_remove_cache() on machines
with large amounts of RAM. quarantine_remove_cache() needs to scan
whole quarantine in order to take out all objects belonging to the
cache. Quarantine is currently 1/32-th of RAM, e.g. on a machine with
256GB of memory that will be 8GB. Moreover quarantine scanning is a
walk over uncached linked list, which is slow.

Add cond_resched() after scanning of each non-empty batch of objects.
Batches are specifically kept of reasonable size for quarantine_put().
On a machine with 256GB of RAM we should have ~512 non-empty batches,
each with 16MB of objects.

Link: http://lkml.kernel.org/r/20170308154239.25440-1-dvyukov@google.com
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/kasan/quarantine.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -282,8 +282,15 @@ void quarantine_remove_cache(struct kmem
on_each_cpu(per_cpu_remove_cache, cache, 1);

spin_lock_irqsave(&quarantine_lock, flags);
- for (i = 0; i < QUARANTINE_BATCHES; i++)
+ for (i = 0; i < QUARANTINE_BATCHES; i++) {
+ if (qlist_empty(&global_quarantine[i]))
+ continue;
qlist_move_cache(&global_quarantine[i], &to_free, cache);
+ /* Scanning whole quarantine can take a while. */
+ spin_unlock_irqrestore(&quarantine_lock, flags);
+ cond_resched();
+ spin_lock_irqsave(&quarantine_lock, flags);
+ }
spin_unlock_irqrestore(&quarantine_lock, flags);

qlist_free_all(&to_free, cache);

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