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
next prev parent reply other threads:[~2019-10-31 3:48 UTC|newest]
Thread overview: 11+ 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 11:36 ` Brian Foster
2019-11-01 4:02 ` Pingfan Liu
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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