From: Pavel Begunkov <[email protected]>
To: Oleg Nesterov <[email protected]>
Cc: [email protected], Jens Axboe <[email protected]>,
Andrew Morton <[email protected]>,
Christian Brauner <[email protected]>,
Tycho Andersen <[email protected]>,
Thomas Gleixner <[email protected]>,
[email protected], Julian Orth <[email protected]>,
Tejun Heo <[email protected]>, Peter Zijlstra <[email protected]>
Subject: Re: [PATCH 2/2] kernel: rerun task_work while freezing in get_signal()
Date: Mon, 8 Jul 2024 16:40:07 +0100 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 7/8/24 11:42, Oleg Nesterov wrote:
> On 07/07, Pavel Begunkov wrote:
>>
>> io_uring can asynchronously add a task_work while the task is getting
>> freezed. TIF_NOTIFY_SIGNAL will prevent the task from sleeping in
>> do_freezer_trap(), and since the get_signal()'s relock loop doesn't
>> retry task_work, the task will spin there not being able to sleep
>> until the freezing is cancelled / the task is killed / etc.
>>
>> Cc: [email protected]
>> Link: https://github.com/systemd/systemd/issues/33626
>> Fixes: 3146cba99aa28 ("io-wq: make worker creation resilient against signals")
>
> I don't think we should blame io_uring even if so far it is the only user
> of TWA_SIGNAL.
And it's not entirely correct even for backporting purposes,
I'll pin it to when freezing was introduced then.
> Perhaps we should change do_freezer_trap() somehow, not sure... It assumes
> that TIF_SIGPENDING is the only reason to not sleep in TASK_INTERRUPTIBLE,
> today this is not true.
Let's CC Peter Zijlstra and Tejun in case they might have
some input on that.
Link to this patch for convenience:
https://lore.kernel.org/all/1d935e9d87fd8672ef3e8a9a0db340d355ea08b4.1720368770.git.asml.silence@gmail.com/
>> --- a/kernel/signal.c
>> +++ b/kernel/signal.c
>> @@ -2694,6 +2694,10 @@ bool get_signal(struct ksignal *ksig)
>> try_to_freeze();
>>
>> relock:
>> + clear_notify_signal();
>> + if (unlikely(task_work_pending(current)))
>> + task_work_run();
>> +
>> spin_lock_irq(&sighand->siglock);
>
> Well, but can't we kill the same code at the start of get_signal() then?
> Of course, in this case get_signal() should check signal_pending(), not
> task_sigpending().
Should be fine, but I didn't want to change the
try_to_freeze() -> __refrigerator() path, which also reschedules.
> Or perhaps something like the patch below makes more sense? I dunno...
It needs a far backporting, I'd really prefer to keep it
lean and without more side effects if possible, unless
there is a strong opinion on that.
> Oleg.
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 1f9dd41c04be..e2ae85293fbb 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2676,6 +2676,7 @@ bool get_signal(struct ksignal *ksig)
> struct signal_struct *signal = current->signal;
> int signr;
>
> +start:
> clear_notify_signal();
> if (unlikely(task_work_pending(current)))
> task_work_run();
> @@ -2760,10 +2761,11 @@ bool get_signal(struct ksignal *ksig)
> if (current->jobctl & JOBCTL_TRAP_MASK) {
> do_jobctl_trap();
> spin_unlock_irq(&sighand->siglock);
> + goto relock;
> } else if (current->jobctl & JOBCTL_TRAP_FREEZE)
> do_freezer_trap();
> -
> - goto relock;
> + goto start;
> + }
> }
>
> /*
>
--
Pavel Begunkov
next prev parent reply other threads:[~2024-07-08 15:40 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-07-07 16:32 [PATCH 0/2] fix task_work interation with freezing Pavel Begunkov
2024-07-07 16:32 ` [PATCH 1/2] io_uring/io-wq: limit retrying worker initialisation Pavel Begunkov
2024-07-07 16:32 ` [PATCH 2/2] kernel: rerun task_work while freezing in get_signal() Pavel Begunkov
2024-07-08 10:42 ` Oleg Nesterov
2024-07-08 15:40 ` Pavel Begunkov [this message]
2024-07-08 18:48 ` Peter Zijlstra
2024-07-09 10:36 ` Oleg Nesterov
2024-07-09 14:05 ` Pavel Begunkov
2024-07-09 16:39 ` Tejun Heo
2024-07-09 19:07 ` Oleg Nesterov
2024-07-09 19:26 ` Pavel Begunkov
2024-07-09 19:38 ` Oleg Nesterov
2024-07-09 19:55 ` Pavel Begunkov
2024-07-10 0:54 ` Tejun Heo
2024-07-10 17:53 ` Pavel Begunkov
2024-07-10 19:10 ` Oleg Nesterov
2024-07-10 19:20 ` Tejun Heo
2024-07-10 21:34 ` Oleg Nesterov
2024-07-10 22:01 ` Tejun Heo
2024-07-10 22:17 ` Oleg Nesterov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox