Re: [PATCH for 4.14] xfs_copy: don't hang if /all/ the targets hit write errors

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Nov 16, 2017 at 07:45:09PM -0800, Darrick J. Wong wrote:
> On Thu, Nov 16, 2017 at 03:10:39PM -0600, Eric Sandeen wrote:
> > 
> > 
> > On 11/15/17 7:14 PM, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > If xfs_copy is told to copy a filesystem and /all/ the writer threads
> > > hit an write error, there won't be any threads to unlock mainwait, which
> > > means that write_wbuf will deadlock with itself trying to lock mainwait.
> > > Therefore, if we discover that all the writer threads are dead, just
> > > bail out.
> > > 
> > > Discovered by running xfs/073 with a tiny test device.
> > > 
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > ---
> > >  copy/xfs_copy.c |   12 ++++++++++++
> > >  1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c
> > > index 33e05df..fb37375 100644
> > > --- a/copy/xfs_copy.c
> > > +++ b/copy/xfs_copy.c
> > > @@ -476,6 +476,7 @@ void
> > >  write_wbuf(void)
> > >  {
> > >  	int		i;
> > > +	int		badness = 0;
> > >  
> > >  	/* verify target threads */
> > >  	for (i = 0; i < num_targets; i++)
> > > @@ -486,6 +487,17 @@ write_wbuf(void)
> > >  	for (i = 0; i < num_targets; i++)
> > >  		if (target[i].state != INACTIVE)
> > >  			pthread_mutex_unlock(&targ[i].wait);	/* wake up */
> > > +		else
> > > +			badness++;
> > > +
> > > +	/*
> > > +	 * If all the targets are inactive then there won't be any io
> > > +	 * threads left to release mainwait.  We're screwed, so bail out.
> > > +	 */
> > > +	if (badness == num_targets) {
> > > +		check_errors();
> > 
> > libxfs_umount(mp); ?
> 
> Doh. v2 on its way

Hmmm.  The other error bailouts don't call libxfs_umount and it hardly
matters since we're exiting anyway.  The mp is a local variable to main
so we'd have to convey abort status out of write_wbuf back to main.
That's a bigger change; do you want me to pursue that instead?

--D

> --D
> 
> > -Eric
> > 
> > > +		exit(1);
> > > +	}
> > >  
> > >  	signal_maskfunc(SIGCHLD, SIG_UNBLOCK);
> > >  	pthread_mutex_lock(&mainwait);
> > > --
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