Thread (11 messages) 11 messages, 4 authors, 2025-09-17

Re: [linux-next20250911]Kernel OOPs while running generic/256 on Pmem device

From: Venkat <hidden>
Date: 2025-09-15 14:22:11
Also in: cgroups, linux-fsdevel, linux-next, linux-xfs, lkml, stable 

quoted hunk ↗ jump to hunk
On 13 Sep 2025, at 8:18 AM, Julian Sun [off-list ref] wrote:

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)
Hello,

Thanks for the fix. This is fixing the reported issue.

While sending out the patch please add below tag as well.

Tested-by: Venkat Rao Bagalkote <redacted>

Regards,
Venkat.
On Fri, Sep 12, 2025 at 8:33 PM Venkat [off-list ref] wrote:
quoted


quoted
On 12 Sep 2025, at 10:51 AM, Venkat Rao Bagalkote [off-list ref] 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 <redacted>



Regards,

Venkat.

After reverting the below commit, issue is not seen.

commit 61bbf51e75df1a94cf6736e311cb96aeb79826a8
Author: Julian Sun [off-list ref]
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:
quoted
quoted
quoted
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.
quoted
quoted
quoted
wb.write_bandwidth
   (unsigned long)24
quoted
quoted
quoted
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 [off-list ref]
   Acked-by: Tejun Heo [off-list ref]
   Cc: Michal Hocko [off-list ref]
   Cc: Roman Gushchin [off-list ref]
   Cc: Johannes Weiner [off-list ref]
   Cc: Shakeel Butt [off-list ref]
   Cc: Muchun Song [off-list ref]
   Cc: [off-list ref]
   Signed-off-by: Andrew Morton [off-list ref]

Regards,
Venkat.

quoted

-- 
Julian Sun [off-list ref]
  



    
  

  
    

      

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