xfs: Fix a deadlock in xfs_log_commit_cil() code path
authorChandra Seetharaman <sekharan@us.ibm.com>
Fri, 19 Jul 2013 22:31:38 +0000 (17:31 -0500)
committerBen Myers <bpm@sgi.com>
Mon, 22 Jul 2013 18:58:10 +0000 (13:58 -0500)
commit297aa63769e6ae06b7db97eb76c9211beeb32c69
tree151526cae76c8c74d22024ff2ef02df37d9888f6
parent58e59854a3dfa9ab1fa1bcfc6324646cd77046a7
xfs: Fix a deadlock in xfs_log_commit_cil() code path

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@us.ibm.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
fs/xfs/xfs_log.c