From: Oleg Nesterov <[email protected]>
To: Pavel Begunkov <[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]>
Subject: Re: [PATCH 2/2] kernel: rerun task_work while freezing in get_signal()
Date: Mon, 8 Jul 2024 12:42:21 +0200 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <1d935e9d87fd8672ef3e8a9a0db340d355ea08b4.1720368770.git.asml.silence@gmail.com>
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.
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.
> --- 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().
Or perhaps something like the patch below makes more sense? I dunno...
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;
+ }
}
/*
next prev parent reply other threads:[~2024-07-08 10:44 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 [this message]
2024-07-08 15:40 ` Pavel Begunkov
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
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