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From: "Theodore Y. Ts'o" <>
To: Dmitry Vyukov <>
Cc: syzbot <>,
	Andreas Dilger <>,
	<>, LKML <>,
	linux-fsdevel <>,
	syzkaller-bugs <>,
	Peter Zijlstra <>,
	Ingo Molnar <>,
	Arnaldo Carvalho de Melo <>
Subject: Re: INFO: rcu detected stall in ext4_file_write_iter
Date: Wed, 27 Feb 2019 16:57:55 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, Feb 27, 2019 at 10:58:50AM +0100, Dmitry Vyukov wrote:
> Peter, Ingo, do you have any updates on the
> perf_event_open/sched_setattr stalls? This bug cause assorted hangs
> throughout kernel and so is nasty.
> syzkaller tries to remove all syscalls from reproducers one-by-one.
> Somehow without sched_setattr the hang did not reproduce (a bunch of
> repros have perf_event_open+sched_setattr so somehow they seem to be
> related)

FWIW, at least for me, the repro.c with sched_setattr commented out
(see the repro.c attached to a message[1] earlier in the thread) it
was reproducing reliably on a 2 CPU, 2 GB memory KVM using the
ext4.git tree (dev branch, 5.0-rc3 plus ext4 commits for the next
merge window) using a Debian stable-based VM[2].


> But even with perfect repros machines still won't be
> able to tell in all cases that even though the hang happened in ext4
> code, the root cause is actually another scheduler-related system
> call. So thanks for looking into this.

To be clear, there was *not* a scheduler-related system call in the
repro.c I was playing with (see [2]); just perf_event_open(2) and


	      	      	    	 		    	- Ted

  reply	other threads:[~2019-02-27 21:58 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2019-02-26 15:17 ` INFO: rcu detected stall in ext4_file_write_iter Theodore Y. Ts'o
2019-02-27  9:58   ` Dmitry Vyukov
2019-02-27 21:57     ` Theodore Y. Ts'o [this message]
2019-02-28  9:34       ` Dmitry Vyukov
2019-03-21 17:30 ` syzbot
2020-09-11 19:33 ` syzbot
2020-09-11 20:03   ` Jens Axboe

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