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From: Pingfan Liu <kernelfans@gmail.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org, Brian Foster <bfoster@redhat.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] xfs/log: protect the logging content under xc_ctx_lock
Date: Thu, 31 Oct 2019 11:48:08 +0800	[thread overview]
Message-ID: <20191031034808.GA479@mypc> (raw)
In-Reply-To: <20191030164825.GJ15222@magnolia>

On Wed, Oct 30, 2019 at 09:48:25AM -0700, Darrick J. Wong wrote:
> On Wed, Oct 30, 2019 at 09:37:11PM +0800, Pingfan Liu wrote:
> > xc_cil_lock is not enough to protect the integrity of a trans logging.
> > Taking the scenario:
> >   cpuA                                 cpuB                          cpuC
> > 
> >   xlog_cil_insert_format_items()
> > 
> >   spin_lock(&cil->xc_cil_lock)
> >   link transA's items to xc_cil,
> >      including item1
> >   spin_unlock(&cil->xc_cil_lock)
> >                                                                       xlog_cil_push() fetches transA's item under xc_cil_lock
> >                                        issue transB, modify item1
> >                                                                       xlog_write(), but now, item1 contains content from transB and we have a broken transA
> > 
> > Survive this race issue by putting under the protection of xc_ctx_lock.
> > Meanwhile the xc_cil_lock can be dropped as xc_ctx_lock does it against
> > xlog_cil_insert_items()
> 
> How did you trigger this race?  Is there a test case to reproduce, or
> did you figure this out via code inspection?
> 
Via code inspection. To hit this bug, the condition is hard to meet:
a broken transA is written to disk, then system encounters a failure before
transB is written. Only if this happens, the recovery will bring us to a
broken context.

Regards,
	Pingfan

  reply	other threads:[~2019-10-31  3:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-30  6:29 [PATCH] xfs/log: protect xc_cil in xlog_cil_push() Pingfan Liu
2019-10-30 12:53 ` Brian Foster
2019-10-30 13:33   ` Pingfan Liu
2019-10-30 13:37     ` [PATCH] xfs/log: protect the logging content under xc_ctx_lock Pingfan Liu
2019-10-30 16:48       ` Darrick J. Wong
2019-10-31  3:48         ` Pingfan Liu [this message]
2019-10-31 21:40       ` Dave Chinner
2019-11-01  3:39         ` Pingfan Liu
2019-10-31 21:25     ` [PATCH] xfs/log: protect xc_cil in xlog_cil_push() Dave Chinner

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