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Date:   Mon, 4 Jan 2021 10:53:20 +0530
From:   Palash Oswal <oswalpalash@...il.com>
To:     Hillf Danton <hdanton@...a.com>, axboe@...nel.dk
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Pavel Begunkov <asml.silence@...il.com>,
        viro@...iv.linux.org.uk, will@...nel.org, rostedt@...dmis.org,
        peterz@...radead.org, mingo@...hat.com, mingo@...nel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: INFO: task hung in __io_uring_task_cancel

Hillf -
> Can you reproduce it again against 5.11-rc1 with the tiny diff applied
> to see if there is a missing wakeup in the mainline?

Hey Hillf, thanks for sharing the diff. It seems like the reproducer
that I had sent did not work on 5.11-rc1 itself, so I'm trying to get
an updated reproducer for that.
I'm not well versed with the io_uring code yet, and therefore it'll
take me longer to get the reproducer going for 5.11-rc1.

Jens -
> Can you see if this helps? The reproducer is pretty brutal, it'll fork
> thousands of tasks with rings! But should work of course. I think this
> one is pretty straight forward, and actually an older issue with the
> poll rewaiting.

Hey Jens, I applied your diff to 5.10.4 (
b1313fe517ca3703119dcc99ef3bbf75ab42bcfb ), and unfortunately, I'm
still seeing the task being hung. Here's the console log if this helps
further -
root@...kaller:~# [  242.840696] INFO: task repro:395 blocked for more
than 120 seconds.
[  242.846353]       Not tainted 5.10.4+ #9
[  242.849951] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[  242.857665] task:repro           state:D stack:    0 pid:  395
ppid:   394 flags:0x00000004
[  242.867346] Call Trace:
[  242.870521]  __schedule+0x28d/0x7e0
[  242.873597]  ? __percpu_counter_sum+0x75/0x90
[  242.876794]  schedule+0x4f/0xc0
[  242.878803]  __io_uring_task_cancel+0xad/0xf0
[  242.880952]  ? wait_woken+0x80/0x80
[  242.882330]  bprm_execve+0x67/0x8a0
[  242.884142]  do_execveat_common+0x1d2/0x220
[  242.885610]  __x64_sys_execveat+0x5d/0x70
[  242.886708]  do_syscall_64+0x38/0x90
[  242.887727]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  242.889298] RIP: 0033:0x7ffabedd6469
[  242.890265] RSP: 002b:00007ffc56b8bc78 EFLAGS: 00000246 ORIG_RAX:
0000000000000142
[  242.892055] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ffabedd6469
[  242.893776] RDX: 0000000000000000 RSI: 0000000020000180 RDI: 00000000ffffffff
[  242.895400] RBP: 00007ffc56b8bc90 R08: 0000000000000000 R09: 00007ffc56b8bc90
[  242.896879] R10: 0000000000000000 R11: 0000000000000246 R12: 0000559c19400bf0
[  242.898335] R13: 00007ffc56b8bdb0 R14: 0000000000000000 R15: 0000000000000000
[  363.691144] INFO: task repro:395 blocked for more than 241 seconds.
[  363.693724]       Not tainted 5.10.4+ #9
[  363.695513] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[  363.700543] task:repro           state:D stack:    0 pid:  395
ppid:   394 flags:0x00000004
[  363.705747] Call Trace:
[  363.707359]  __schedule+0x28d/0x7e0
[  363.709603]  ? __percpu_counter_sum+0x75/0x90
[  363.712900]  schedule+0x4f/0xc0
[  363.715002]  __io_uring_task_cancel+0xad/0xf0
[  363.718026]  ? wait_woken+0x80/0x80
[  363.720137]  bprm_execve+0x67/0x8a0
[  363.721992]  do_execveat_common+0x1d2/0x220
[  363.723997]  __x64_sys_execveat+0x5d/0x70
[  363.725857]  do_syscall_64+0x38/0x90
[  363.727501]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  363.729510] RIP: 0033:0x7ffabedd6469
[  363.730913] RSP: 002b:00007ffc56b8bc78 EFLAGS: 00000246 ORIG_RAX:
0000000000000142
[  363.733747] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ffabedd6469
[  363.736138] RDX: 0000000000000000 RSI: 0000000020000180 RDI: 00000000ffffffff
[  363.738431] RBP: 00007ffc56b8bc90 R08: 0000000000000000 R09: 00007ffc56b8bc90
[  363.740504] R10: 0000000000000000 R11: 0000000000000246 R12: 0000559c19400bf0
[  363.742560] R13: 00007ffc56b8bdb0 R14: 0000000000000000 R15: 0000000000000000

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