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Date: Wed, 2 Apr 2025 14:24:47 +0200
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From: Sebastian Sewior <bigeasy@linutronix.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Ziljstra <peterz@infradead.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
	Jiri Olsa <jolsa@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: uprobe splat in PREEMP_RT
Message-ID: <20250402122447.B3XIrQnG@linutronix.de>
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In-Reply-To: <20250402121850.GI22091@redhat.com>

On 2025-04-02 14:18:51 [+0200], Oleg Nesterov wrote:
> On 04/02, Sebastian Sewior wrote:

I need to tell mutt to replace my name in case it is misspelled.

> > The preempted ri_timer() could stall a read_seqcount_begin().
> 
> Again, nobody use read_seqcount_begin(utask->ri_seqcount).
> 
> free_ret_instance() uses raw_seqcount_try_begin(utask->ri_seqcount),
> which, since ri_seqcount is seqcount_t, is just smp_load_acquire().
> This can't stall.

Yes. This would work for here just to skip the check because of all
details that are hard to express. Therefore I suggested to use
raw_write_seqcount_begin() instead of write_seqcount_begin() in
20250402122158.j_8VoHQ-@linutronix.de. Would that work?

> Oleg.

Sebastian