Hi,
Does this fix make sense to you?
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d0dfaa0ccaba..ed24dcece56a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3945,9 +3945,10 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css) * Not necessary to wait for wb completion which might cause task hung, * only used to free resources. See memcg_cgwb_waitq_callback_fn(). */ - __add_wait_queue_entry_tail(wait->done.waitq, &wait->wq_entry); if (atomic_dec_and_test(&wait->done.cnt)) - wake_up_all(wait->done.waitq); + kfree(wait); + else + __add_wait_queue_entry_tail(wait->done.waitq, &wait->wq_entry);; } #endif if (cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_nosocket)
On Fri, Sep 12, 2025 at 8:33 PM Venkat venkat88@linux.ibm.com wrote:
On 12 Sep 2025, at 10:51 AM, Venkat Rao Bagalkote venkat88@linux.ibm.com wrote:
Greetings!!!
IBM CI has reported a kernel crash, while running generic/256 test case on pmem device from xfstests suite on linux-next20250911 kernel.
xfstests: git://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
local.config:
[xfs_dax] export RECREATE_TEST_DEV=true export TEST_DEV=/dev/pmem0 export TEST_DIR=/mnt/test_pmem export SCRATCH_DEV=/dev/pmem0.1 export SCRATCH_MNT=/mnt/scratch_pmem export MKFS_OPTIONS="-m reflink=0 -b size=65536 -s size=512" export FSTYP=xfs export MOUNT_OPTIONS="-o dax"
Test case: generic/256
Traces:
[ 163.371929] ------------[ cut here ]------------ [ 163.371936] kernel BUG at lib/list_debug.c:29! [ 163.371946] Oops: Exception in kernel mode, sig: 5 [#1] [ 163.371954] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=8192 NUMA pSeries [ 163.371965] Modules linked in: xfs nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack bonding tls nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables nfnetlink sunrpc pseries_rng vmx_crypto dax_pmem fuse ext4 crc16 mbcache jbd2 nd_pmem papr_scm sd_mod libnvdimm sg ibmvscsi ibmveth scsi_transport_srp pseries_wdt [ 163.372127] CPU: 22 UID: 0 PID: 130 Comm: kworker/22:0 Kdump: loaded Not tainted 6.17.0-rc5-next-20250911 #1 VOLUNTARY [ 163.372142] Hardware name: IBM,9080-HEX Power11 (architected) 0x820200 0xf000007 of:IBM,FW1110.01 (NH1110_069) hv:phyp pSeries [ 163.372155] Workqueue: cgroup_free css_free_rwork_fn [ 163.372169] NIP: c000000000d051d4 LR: c000000000d051d0 CTR: 0000000000000000 [ 163.372176] REGS: c00000000ba079b0 TRAP: 0700 Not tainted (6.17.0-rc5-next-20250911) [ 163.372183] MSR: 800000000282b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28000000 XER: 00000006 [ 163.372214] CFAR: c0000000002bae9c IRQMASK: 0 [ 163.372214] GPR00: c000000000d051d0 c00000000ba07c50 c00000000230a600 0000000000000075 [ 163.372214] GPR04: 0000000000000004 0000000000000001 c000000000507e2c 0000000000000001 [ 163.372214] GPR08: c000000d0cb87d13 0000000000000000 0000000000000000 a80e000000000000 [ 163.372214] GPR12: c00e0001a1970fa2 c000000d0ddec700 c000000000208e58 c000000107b5e190 [ 163.372214] GPR16: c00000000d3e5d08 c00000000b71cf78 c00000000d3e5d05 c00000000b71cf30 [ 163.372214] GPR20: c00000000b71cf08 c00000000b71cf10 c000000019f58588 c000000004704bc8 [ 163.372214] GPR24: c000000107b5e100 c000000004704bd0 0000000000000003 c000000004704bd0 [ 163.372214] GPR28: c000000004704bc8 c000000019f585a8 c000000019f53da8 c000000004704bc8 [ 163.372315] NIP [c000000000d051d4] __list_add_valid_or_report+0x124/0x188 [ 163.372326] LR [c000000000d051d0] __list_add_valid_or_report+0x120/0x188 [ 163.372335] Call Trace: [ 163.372339] [c00000000ba07c50] [c000000000d051d0] __list_add_valid_or_report+0x120/0x188 (unreliable) [ 163.372352] [c00000000ba07ce0] [c000000000834280] mem_cgroup_css_free+0xa0/0x27c [ 163.372363] [c00000000ba07d50] [c0000000003ba198] css_free_rwork_fn+0xd0/0x59c [ 163.372374] [c00000000ba07da0] [c0000000001f5d60] process_one_work+0x41c/0x89c [ 163.372385] [c00000000ba07eb0] [c0000000001f76c0] worker_thread+0x558/0x848 [ 163.372394] [c00000000ba07f80] [c000000000209038] kthread+0x1e8/0x230 [ 163.372406] [c00000000ba07fe0] [c00000000000ded8] start_kernel_thread+0x14/0x18 [ 163.372416] Code: 4b9b1099 60000000 7f63db78 4bae8245 60000000 e8bf0008 3c62ff88 7fe6fb78 7fc4f378 38637d40 4b5b5c89 60000000 <0fe00000> 60000000 60000000 7f83e378 [ 163.372453] ---[ end trace 0000000000000000 ]--- [ 163.380581] pstore: backend (nvram) writing error (-1) [ 163.380593]
If you happen to fix this issue, please add below tag.
Reported-by: Venkat Rao Bagalkote venkat88@linux.ibm.com
Regards,
Venkat.
After reverting the below commit, issue is not seen.
commit 61bbf51e75df1a94cf6736e311cb96aeb79826a8 Author: Julian Sun sunjunchao@bytedance.com Date: Thu Aug 28 04:45:57 2025 +0800
memcg: don't wait writeback completion when release memcg Recently, we encountered the following hung task: INFO: task kworker/4:1:1334558 blocked for more than 1720 seconds. [Wed Jul 30 17:47:45 2025] Workqueue: cgroup_destroy css_free_rwork_fn [Wed Jul 30 17:47:45 2025] Call Trace: [Wed Jul 30 17:47:45 2025] __schedule+0x934/0xe10 [Wed Jul 30 17:47:45 2025] ? complete+0x3b/0x50 [Wed Jul 30 17:47:45 2025] ? _cond_resched+0x15/0x30 [Wed Jul 30 17:47:45 2025] schedule+0x40/0xb0 [Wed Jul 30 17:47:45 2025] wb_wait_for_completion+0x52/0x80 [Wed Jul 30 17:47:45 2025] ? finish_wait+0x80/0x80 [Wed Jul 30 17:47:45 2025] mem_cgroup_css_free+0x22/0x1b0 [Wed Jul 30 17:47:45 2025] css_free_rwork_fn+0x42/0x380 [Wed Jul 30 17:47:45 2025] process_one_work+0x1a2/0x360 [Wed Jul 30 17:47:45 2025] worker_thread+0x30/0x390 [Wed Jul 30 17:47:45 2025] ? create_worker+0x1a0/0x1a0 [Wed Jul 30 17:47:45 2025] kthread+0x110/0x130 [Wed Jul 30 17:47:45 2025] ? __kthread_cancel_work+0x40/0x40 [Wed Jul 30 17:47:45 2025] ret_from_fork+0x1f/0x30 The direct cause is that memcg spends a long time waiting for dirty page writeback of foreign memcgs during release. The root causes are: a. The wb may have multiple writeback tasks, containing millions of dirty pages, as shown below: >>> for work in list_for_each_entry("struct wb_writeback_work", \ wb.work_list.address_of_(), "list"): ... print(work.nr_pages, work.reason, hex(work)) ... 900628 WB_REASON_FOREIGN_FLUSH 0xffff969e8d956b40 1116521 WB_REASON_FOREIGN_FLUSH 0xffff9698332a9540 1275228 WB_REASON_FOREIGN_FLUSH 0xffff969d9b444bc0 1099673 WB_REASON_FOREIGN_FLUSH 0xffff969f0954d6c0 1351522 WB_REASON_FOREIGN_FLUSH 0xffff969e76713340 2567437 WB_REASON_FOREIGN_FLUSH 0xffff9694ae208400 2954033 WB_REASON_FOREIGN_FLUSH 0xffff96a22d62cbc0 3008860 WB_REASON_FOREIGN_FLUSH 0xffff969eee8ce3c0 3337932 WB_REASON_FOREIGN_FLUSH 0xffff9695b45156c0 3348916 WB_REASON_FOREIGN_FLUSH 0xffff96a22c7a4f40 3345363 WB_REASON_FOREIGN_FLUSH 0xffff969e5d872800 3333581 WB_REASON_FOREIGN_FLUSH 0xffff969efd0f4600 3382225 WB_REASON_FOREIGN_FLUSH 0xffff969e770edcc0 3418770 WB_REASON_FOREIGN_FLUSH 0xffff96a252ceea40 3387648 WB_REASON_FOREIGN_FLUSH 0xffff96a3bda86340 3385420 WB_REASON_FOREIGN_FLUSH 0xffff969efc6eb280 3418730 WB_REASON_FOREIGN_FLUSH 0xffff96a348ab1040 3426155 WB_REASON_FOREIGN_FLUSH 0xffff969d90beac00 3397995 WB_REASON_FOREIGN_FLUSH 0xffff96a2d7288800 3293095 WB_REASON_FOREIGN_FLUSH 0xffff969dab423240 3293595 WB_REASON_FOREIGN_FLUSH 0xffff969c765ff400 3199511 WB_REASON_FOREIGN_FLUSH 0xffff969a72d5e680 3085016 WB_REASON_FOREIGN_FLUSH 0xffff969f0455e000 3035712 WB_REASON_FOREIGN_FLUSH 0xffff969d9bbf4b00 b. The writeback might severely throttled by wbt, with a speed possibly less than 100kb/s, leading to a very long writeback time. >>> wb.write_bandwidth (unsigned long)24 >>> wb.write_bandwidth (unsigned long)13 The wb_wait_for_completion() here is probably only used to prevent use-after-free. Therefore, we manage 'done' separately and automatically free it. This allows us to remove wb_wait_for_completion() while preventing the use-after-free issue. com Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing") Signed-off-by: Julian Sun <sunjunchao@bytedance.com> Acked-by: Tejun Heo <tj@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Shakeel Butt <shakeelb@google.com> Cc: Muchun Song <songmuchun@bytedance.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>Regards, Venkat.