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Message-ID: <CAHSKhteezz0pjUYibp6drOysBzxUV6LzSi6oyA8LgHCtL_CysA@mail.gmail.com>
Date: Tue, 16 Sep 2025 02:17:04 +0800
From: Julian Sun <sunjunchao@...edance.com>
To: Venkat <venkat88@...ux.ibm.com>
Cc: tj@...nel.org, akpm@...ux-foundation.org, stable@...r.kernel.org,
songmuchun@...edance.com, shakeelb@...gle.com, hannes@...xchg.org,
roman.gushchin@...ux.dev, mhocko@...e.com,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, riteshh@...ux.ibm.com,
ojaswin@...ux.ibm.com, linux-fsdevel@...r.kernel.org,
linux-xfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Madhavan Srinivasan <maddy@...ux.ibm.com>, Linux Next Mailing List <linux-next@...r.kernel.org>,
cgroups@...r.kernel.org, linux-mm@...r.kernel.org
Subject: Re: [External] Re: [linux-next20250911]Kernel OOPs while running
generic/256 on Pmem device
Hi,
On Mon, Sep 15, 2025 at 10:20 PM Venkat <venkat88@...ux.ibm.com> wrote:
>
>
>
> > On 13 Sep 2025, at 8:18 AM, Julian Sun <sunjunchao@...edance.com> 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.
Thanks for your testing and feedback.
>
> While sending out the patch please add below tag as well.
>
> Tested-by: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
Sure. That's how it should be.
Could you please try again with the following patch? The previous one
might have caused a memory leak and had race conditions. I can’t
reproduce it locally...
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 80257dba30f8..35da16928599 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3940,6 +3940,7 @@ static void mem_cgroup_css_free(struct
cgroup_subsys_state *css)
int __maybe_unused i;
#ifdef CONFIG_CGROUP_WRITEBACK
+ spin_lock(&memcg_cgwb_frn_waitq.lock);
for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) {
struct cgwb_frn_wait *wait = memcg->cgwb_frn[i].wait;
@@ -3948,9 +3949,12 @@ static void mem_cgroup_css_free(struct
cgroup_subsys_state *css)
* 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);
+ if (atomic_dec_and_test(&wait->done.cnt)) {
+ list_del(&wait->wq_entry.entry);
+ kfree(wait);
+ }
}
+ spin_unlock(&memcg_cgwb_frn_waitq.lock);
#endif
if (cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_nosocket)
static_branch_dec(&memcg_sockets_enabled_key);
>
> Regards,
> Venkat.
> >
> > On Fri, Sep 12, 2025 at 8:33 PM Venkat <venkat88@...ux.ibm.com> wrote:
> >>
> >>
> >>
> >>> On 12 Sep 2025, at 10:51 AM, Venkat Rao Bagalkote <venkat88@...ux.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@...ux.ibm.com>
> >>>
> >>>
> >>>
> >>> Regards,
> >>>
> >>> Venkat.
> >>>
> >>>
> >>
> >> After reverting the below commit, issue is not seen.
> >>
> >> commit 61bbf51e75df1a94cf6736e311cb96aeb79826a8
> >> Author: Julian Sun <sunjunchao@...edance.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@...edance.com>
> >> Acked-by: Tejun Heo <tj@...nel.org>
> >> Cc: Michal Hocko <mhocko@...e.com>
> >> Cc: Roman Gushchin <roman.gushchin@...ux.dev>
> >> Cc: Johannes Weiner <hannes@...xchg.org>
> >> Cc: Shakeel Butt <shakeelb@...gle.com>
> >> Cc: Muchun Song <songmuchun@...edance.com>
> >> Cc: <stable@...r.kernel.org>
> >> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> >>
> >> Regards,
> >> Venkat.
> >>
> >>>
> >>
> >
> >
> > --
> > Julian Sun <sunjunchao@...edance.com>
>
Thanks,
--
Julian Sun <sunjunchao@...edance.com>
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