mainline inclusion from mainline-v6.14-rc4 commit 99333229dee41b992f3b0493f6aa2e3528138384 category: bugfix bugzilla: https://atomgit.com/openeuler/kernel/issues/78 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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@huaweicloud.com Fixes: b6e6edcfa405 ("mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage") Signed-off-by: Chen Ridong <chenridong@huawei.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Muchun Song <songmuchun@bytedance.com> Cc: Wang Weiyang <wangweiyang2@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Chen Ridong <chenridong@huawei.com> --- mm/memcontrol.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 7a8795130546d..067a3dde6f87f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -8030,6 +8030,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, 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); -- 2.34.1