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Re: [PATCH] xfs: Fix a deadlock in xfs_log_commit_cil() code path

To: Chandra Seetharaman <sekharan@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: Fix a deadlock in xfs_log_commit_cil() code path
From: Ben Myers <bpm@xxxxxxx>
Date: Mon, 22 Jul 2013 13:53:43 -0500
Cc: XFS mailing list <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1374273098.8941.2075.camel@xxxxxxxxxxxxxxxxxx>
References: <1374273098.8941.2075.camel@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Fri, Jul 19, 2013 at 05:31:38PM -0500, Chandra Seetharaman wrote:
> 
> While testing and rearranging pquota/gquota code, I stumbled
> on a xfs_shutdown() during a mount. But the mount just hung.
> 
> Debugged and found that there is a deadlock involving
> &log->l_cilp->xc_ctx_lock.
> 
> It is in a code path where &log->l_cilp->xc_ctx_lock is first
> acquired in read mode and some levels down the same semaphore
> is being acquired in write mode causing a deadlock.
> 
> This is the stack:
> xfs_log_commit_cil -> acquires &log->l_cilp->xc_ctx_lock in read mode
>   xlog_print_tic_res
>     xfs_force_shutdown
>       xfs_log_force_umount
>         xlog_cil_force
>           xlog_cil_force_lsn
>             xlog_cil_push_foreground
>               xlog_cil_push - tries to acquire same semaphore in write mode
> 
> This patch fixes the deadlock by changing the reason code for
> xfs_force_shutdown in xlog_print_tic_res() to SHUTDOWN_LOG_IO_ERROR.
> 
> SHUTDOWN_LOG_IO_ERROR is the right reason code to be set since
> we are in the log path.
> 
> Thanks to Dave for suggesting this solution.
> 
> Signed-off-by: Chandra Seetharaman <sekharan@xxxxxxxxxx>

Looks fine.

Reviewed-by: Ben Myers <bpm@xxxxxxx>

Applied.

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