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Date: Thu, 6 Oct 2016 14:12:47 -0400 (EDT)
From: CAI Qian <caiqian@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT]
 splice_read reworked)
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----- Original Message -----
> From: "Linus Torvalds" <torvalds@linux-foundation.org>
> To: "CAI Qian" <caiqian@redhat.com>
> Cc: "Al Viro" <viro@zeniv.linux.org.uk>, "tj" <tj@kernel.org>, "Dave Chinner" <david@fromorbit.com>, "linux-xfs"
> <linux-xfs@vger.kernel.org>, "Jens Axboe" <axboe@kernel.dk>, "Nick Piggin" <npiggin@gmail.com>, "linux-fsdevel"
> <linux-fsdevel@vger.kernel.org>
> Sent: Thursday, October 6, 2016 1:00:08 PM
> Subject: Re: local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked)
> 
> On Thu, Oct 6, 2016 at 9:11 AM, CAI Qian <caiqian@redhat.com> wrote:
> >
> >>
> >> Wait. There is also a lockep happened before the xfs internal error as
> >> well.
> > Some other lockdep this time,
> 
> This one looks just bogus.
> 
> > [ 4872.569797]  Possible unsafe locking scenario:
> > [ 4872.569797]
> > [ 4872.576401]        CPU0
> > [ 4872.579127]        ----
> > [ 4872.581854]   lock(&xfs_nondir_ilock_class);
> > [ 4872.586637]   <Interrupt>
> > [ 4872.589558]     lock(&xfs_nondir_ilock_class);
> 
> I'm not seeing that .lock taken in interrupt context.
> 
> I'm wondering how many of your reports are confused by earlier errors
> that  happened.
Hmm, there was no previous error/lockdep/warnings on the console prior to
this AFAICT. It was a fresh trinity run after reboot.

The previous run triggered seq_read/__sb_start_write lockdep and
then xfs XFS_WANT_CORRUPTED_RETURN internal error was highlighted
in another reply was also started from a fresh reboot.

After all of those individual runs it will reliably triggered the
cgroup hang from any systemctl command or "make install" of kernel etc.
   CAI Qian