Re: Bad psi_group_cpu.tasks[NR_MEMSTALL] counter

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2024/11/28 18:00, Max Kellermann wrote:
> On Thu, Nov 21, 2024 at 2:18 PM Gao Xiang <hsiangkao@linux.alibaba.com> wrote:
>> Just saw this. I guess your _recent_ 6.11.9 bug is actually
>> related to EROFS since EROFS uses readahead_expand().  I think
>> your recent report was introduced by a recent backport fix
>> commit 9e2f9d34dd12 ("erofs: handle overlapped pclusters out of crafted images properly")
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v6.11.9&id=9cfa199bcbbbba31cbf97b2786f44f4464f3f29a
>>
>> bio can be NULL after this patch and causes
>> unbalanced psi_memstall_{enter,leave}().  It can be fixed as
>> (the diff below could be damaged due to my email client):
> 
> With your patch, the PSI warning (from Suren's debugging patch) fired
> again last night. Which means there may be other instances of this bug
> left.

Ok, but honestly that is somewhat strange, on the
EROFS side readahead_expand() can only be used in
.readahead() context and with the original
readahead_control.

I don't have more clues without more understanding
of psi memstall.  From my limited POV, the callers
of psi_memstall_{enter,leave}() all seem good.

Thanks,
Gao Xiang

> 
>   ------------[ cut here ]------------
>   Stall from readahead_expand+0xca/0x1d0 was never cleared
>   WARNING: CPU: 133 PID: 91645 at kernel/sched/psi.c:989
> psi_task_switch+0x126/0x230
>   Modules linked in:
>   CPU: 133 UID: 3221274747 PID: 91645 Comm: php-cgi8.1 Tainted: G
>   W          6.11.10-cm4all2-es+ #267
>   Tainted: [W]=WARN
>   Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023
>   RIP: 0010:psi_task_switch+0x126/0x230
>   Code: f6 75 e6 41 f6 44 24 18 80 74 36 41 f6 84 24 d0 08 00 00 02 74
> 2b 49 8b b4 24 d8 08 00 00 48 c7 c7 20 c8 8d a8 e8 fa 1f f9 ff <0f> 0b
> 41 f6 44 24 18 80 74 0d 41 f6 84 24 d0 08 00 00 02 74 02 0f
>   RSP: 0018:ffff96be9c28b9a8 EFLAGS: 00010086
>   RAX: 0000000000000000 RBX: 0000000000000085 RCX: 0000000000000027
>   RDX: ffff8997b995c8c8 RSI: 0000000000000001 RDI: ffff8997b995c8c0
>   RBP: 000000000000001c R08: 00000000ffff7fff R09: 0000000000000058
>   R10: 00000000ffff7fff R11: ffff899abd2a1000 R12: ffff891db3b85c00
>   R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>   FS:  0000000000000000(0000) GS:ffff8997b9940000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 00007f26d7aba480 CR3: 000000c07c61a006 CR4: 0000000000770ef0
>   PKRU: 55555554
>   Call Trace:
>    <TASK>
>    ? __warn+0x93/0x140
>    ? psi_task_switch+0x126/0x230
>    ? report_bug+0x174/0x1a0
>    ? handle_bug+0x53/0x90
>    ? exc_invalid_op+0x17/0x70
>    ? asm_exc_invalid_op+0x16/0x20
>    ? psi_task_switch+0x126/0x230
>    ? psi_task_switch+0x126/0x230
>    __schedule+0x980/0x10f0
>    do_task_dead+0x3e/0x40
>    do_exit+0x6ed/0x970
>    do_group_exit+0x2c/0x80
>    __x64_sys_exit_group+0x14/0x20
>    x64_sys_call+0x15aa/0x17b0
>    do_syscall_64+0x64/0x100
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? get_page_from_freelist+0x60e/0x1140
>    ? cgroup_rstat_updated+0x88/0x210
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? __mod_memcg_lruvec_state+0x91/0x140
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? __lruvec_stat_mod_folio+0x80/0xd0
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? folio_add_file_rmap_ptes+0x37/0xb0
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? set_pte_range+0xb7/0x280
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? next_uptodate_folio+0x83/0x270
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? filemap_map_pages+0x4a2/0x590
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? do_fault+0x291/0x4d0
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? __handle_mm_fault+0x31c/0x1060
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? __count_memcg_events+0x53/0xf0
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? handle_mm_fault+0xb6/0x280
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? do_user_addr_fault+0x386/0x610
>    ? srso_alias_return_thunk+0x5/0xfbef5
>    ? exc_page_fault+0x6f/0x120
>    entry_SYSCALL_64_after_hwframe+0x76/0x7e
>   RIP: 0033:0x7f26dad48349
>   Code: Unable to access opcode bytes at 0x7f26dad4831f.
>   RSP: 002b:00007ffcd05a7848 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
>   RAX: ffffffffffffffda RBX: 00007f26dae429e0 RCX: 00007f26dad48349
>   RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
>   RBP: 0000000000000000 R08: fffffffffffffd48 R09: 000055c238e82190
>   R10: 00007f26d8a781a8 R11: 0000000000000246 R12: 00007f26dae429e0
>   R13: 00007f26dae482e0 R14: 000000000000001e R15: 00007f26dae482c8
>    </TASK>
>   ---[ end trace 0000000000000000 ]---