The patch titled
Subject: memcg: avoid dead loop when setting memory.max
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
memcg-avoid-dead-loop-when-setting-memorymax.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-avoid-dead-loop-when-setting-memorymax.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Chen Ridong <chenridong@xxxxxxxxxx>
Subject: memcg: avoid dead loop when setting memory.max
Date: Tue, 11 Feb 2025 08:18:19 +0000
A softlockup issue was found with stress test:
watchdog: BUG: soft lockup - CPU#27 stuck for 26s! [migration/27:181]
CPU: 27 UID: 0 PID: 181 Comm: migration/27 6.14.0-rc2-next-20250210 #1
Stopper: multi_cpu_stop <- stop_machine_from_inactive_cpu
RIP: 0010:stop_machine_yield+0x2/0x10
RSP: 0000:ff4a0dcecd19be48 EFLAGS: 00000246
RAX: ffffffff89c0108f RBX: ff4a0dcec03afe44 RCX: 0000000000000000
RDX: ff1cdaaf6eba5808 RSI: 0000000000000282 RDI: ff1cda80c1775a40
RBP: 0000000000000001 R08: 00000011620096c6 R09: 7fffffffffffffff
R10: 0000000000000001 R11: 0000000000000100 R12: ff1cda80c1775a40
R13: 0000000000000000 R14: 0000000000000001 R15: ff4a0dcec03afe20
FS: 0000000000000000(0000) GS:ff1cdaaf6eb80000(0000)
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000025e2c2a001 CR4: 0000000000773ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
multi_cpu_stop+0x8f/0x100
cpu_stopper_thread+0x90/0x140
smpboot_thread_fn+0xad/0x150
kthread+0xc2/0x100
ret_from_fork+0x2d/0x50
The stress test involves CPU hotplug operations and memory control group
(memcg) operations. The scenario can be described as follows:
echo xx > memory.max cache_ap_online oom_reaper
(CPU23) (CPU50)
xx < usage stop_machine_from_inactive_cpu
for(;;) // all active cpus
trigger OOM queue_stop_cpus_work
// waiting oom_reaper
multi_cpu_stop(migration/xx)
// sync all active cpus ack
// waiting cpu23 ack
// CPU50 loops in multi_cpu_stop
waiting cpu50
Detailed explanation:
1. When the usage is larger than xx, an OOM may be triggered. If the
process does not handle with ths kill signal immediately, it will loop
in the memory_max_write.
2. When cache_ap_online is triggered, the multi_cpu_stop is queued to the
active cpus. Within the multi_cpu_stop function, it attempts to
synchronize the CPU states. However, the CPU23 didn't acknowledge
because it is stuck in a loop within the for(;;).
3. The oom_reaper process is blocked because CPU50 is in a loop, waiting
for CPU23 to acknowledge the synchronization request.
4. Finally, it formed cyclic dependency and lead to softlockup and dead
loop.
To fix this issue, add cond_resched() in the memory_max_write, so that it
will not block migration task.
Link: https://lkml.kernel.org/r/20250211081819.33307-1-chenridong@xxxxxxxxxxxxxxx
Fixes: b6e6edcfa405 ("mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage")
Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Wang Weiyang <wangweiyang2@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 1 +
1 file changed, 1 insertion(+)
--- a/mm/memcontrol.c~memcg-avoid-dead-loop-when-setting-memorymax
+++ a/mm/memcontrol.c
@@ -4166,6 +4166,7 @@ static ssize_t memory_max_write(struct k
memcg_memory_event(memcg, MEMCG_OOM);
if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0))
break;
+ cond_resched();
}
memcg_wb_domain_size_changed(memcg);
_
Patches currently in -mm which might be from chenridong@xxxxxxxxxx are
memcg-avoid-dead-loop-when-setting-memorymax.patch
memcg-use-ofp_peak_unset-instead-of-1.patch
memcg-call-the-free-function-when-allocation-of-pn-fails.patch
memcg-factor-out-the-replace_stock_objcg-function.patch
memcg-add-config_memcg_v1-for-local-functions.patch
