[1/2] mm, memcg: Fix corruption on 64-bit divisor in memory.high throttling
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Message ID 80780887060514967d414b3cd91f9a316a16ab98.1584036142.git.chris@chrisdown.name
State Accepted
Commit d397a45fc741c80c32a14e2de008441e9976f50c
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  • [1/2] mm, memcg: Fix corruption on 64-bit divisor in memory.high throttling
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Commit Message

Chris Down March 12, 2020, 6:02 p.m. UTC
0e4b01df8659 had a bunch of fixups to use the right division method.
However, it seems that after all that it still wasn't right -- div_u64
takes a 32-bit divisor.

The headroom is still large (2^32 pages), so on mundane systems you
won't hit this, but this should definitely be fixed.

Fixes: 0e4b01df8659 ("mm, memcg: throttle allocators when failing reclaim over memory.high")
Reported-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-mm@kvack.org
Cc: cgroups@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com
Cc: stable@vger.kernel.org # 5.4.x
---
 mm/memcontrol.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Johannes Weiner March 16, 2020, 4:19 p.m. UTC | #1
On Thu, Mar 12, 2020 at 06:02:54PM +0000, Chris Down wrote:
> 0e4b01df8659 had a bunch of fixups to use the right division method.
> However, it seems that after all that it still wasn't right -- div_u64
> takes a 32-bit divisor.
> 
> The headroom is still large (2^32 pages), so on mundane systems you
> won't hit this, but this should definitely be fixed.
> 
> Fixes: 0e4b01df8659 ("mm, memcg: throttle allocators when failing reclaim over memory.high")
> Reported-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Chris Down <chris@chrisdown.name>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: linux-mm@kvack.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kernel-team@fb.com
> Cc: stable@vger.kernel.org # 5.4.x

div_u64 versus div64_u64 is really a handgrenade. We just fixed a
bunch of those in psi as well.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Patch
diff mbox series

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63bb6a2aab81..a70206e516fe 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2339,7 +2339,7 @@  void mem_cgroup_handle_over_high(void)
 	 */
 	clamped_high = max(high, 1UL);
 
-	overage = div_u64((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT,
+	overage = div64_u64((u64)(usage - high) << MEMCG_DELAY_PRECISION_SHIFT,
 			  clamped_high);
 
 	penalty_jiffies = ((u64)overage * overage * HZ)