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Date: Fri, 7 Jun 2024 23:22:59 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Wei Fu <fuweid89@gmail.com>
Cc: Sudhanva.Huruli@microsoft.com, akpm@linux-foundation.org,
	apais@linux.microsoft.com, axboe@kernel.dk, boqun.feng@gmail.com,
	brauner@kernel.org, ebiederm@xmission.com, frederic@kernel.org,
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	qiang.zhang1211@gmail.com, rachelmenge@linux.microsoft.com,
	rcu@vger.kernel.org, rostedt@goodmis.org, weifu@microsoft.com
Subject: Re: [RCU] zombie task hung in synchronize_rcu_expedited
Message-ID: <20240607212116.GA7258@redhat.com>
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 <20240607150443.2096063-1-fuweid89@gmail.com>
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On 06/07, Wei Fu wrote:
>
> Yes. I applied your patch on v5.15.160 and run reproducer for 5 hours.
> I didn't see this issue. Currently, it looks good!. I will continue that test
> on this weekend.

Great, thanks!

> In last reply, you mentioned TIF_NOTIFY_SIGNAL related to busy-wait loop.
> Would you please explain why flag-clear works here?

Sure, I'll write the changelog with the explanation and send the patch on
weekend. If it passes your testing.

But in short this is very simple. zap_pid_ns_processes() clears TIF_SIGPENDING
exactly because we want to avoid the busy-wait loop. But today this is not
enough to make signal_pending() return F, see
include/linux/sched/signal.h:signal_pending().

Thanks,

Oleg.