Re: quotacheck deadlock?

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

On Thu, Jul 20, 2017 at 11:58:55AM -0700, Darrick J. Wong wrote:
> On Thu, Jul 20, 2017 at 08:38:46AM -0400, Brian Foster wrote:
> > On Wed, Jul 19, 2017 at 11:58:04PM -0700, Darrick J. Wong wrote:
> > > Hi,
> > > 
> > > I ran the following sequence of commands on 4.13-rc1:
> > > 
> > > # mkfs.xfs -f /dev/sdf
> > > # xfs_db -x -c 'sb 0' -c 'addr rootino' -c 'write -d core.uid 4294967295' /dev/sdf
> > > # mount /dev/sdf -o usrquota
> > > 
> > > The kernel reports that it's starting quotacheck, but never finishes.
> > > echo t > /proc/sysrq produces this for the hung mount command:
> > > 
> > > mount           R  running task        0   988    895 0x00000000
> > > Call Trace:
> > >  ? sched_clock_cpu+0xa8/0xe0
> > >  ? xfs_qm_flush_one+0x3c/0x120 [xfs]
> > >  ? lock_acquire+0xac/0x200
> > >  ? lock_acquire+0xac/0x200
> > >  ? xfs_qm_flush_one+0x3c/0x120 [xfs]
> > >  ? xfs_qm_dquot_walk+0xa1/0x170 [xfs]
> > >  ? get_lock_stats+0x19/0x60
> > >  ? get_lock_stats+0x19/0x60
> > >  ? xfs_qm_dquot_walk+0xa1/0x170 [xfs]
> > >  ? xfs_qm_dquot_walk+0x125/0x170 [xfs]
> > >  ? radix_tree_gang_lookup+0xd1/0xf0
> > >  ? xfs_qm_shrink_count+0x20/0x20 [xfs]
> > >  ? xfs_qm_dquot_walk+0xbb/0x170 [xfs]
> > >  ? kfree+0x23f/0x2d0
> > >  ? kvfree+0x2a/0x40
> > >  ? xfs_bulkstat+0x315/0x680 [xfs]
> > >  ? xfs_qm_get_rtblks+0xa0/0xa0 [xfs]
> > >  ? xfs_qm_quotacheck+0x2bd/0x360 [xfs]
> > >  ? xfs_qm_mount_quotas+0x106/0x1f0 [xfs]
> > >  ? xfs_mountfs+0x6f2/0xb00 [xfs]
> > >  ? xfs_fs_fill_super+0x483/0x610 [xfs]
> > >  ? mount_bdev+0x180/0x1b0
> > >  ? xfs_finish_flags+0x150/0x150 [xfs]
> > >  ? xfs_fs_mount+0x15/0x20 [xfs]
> > >  ? mount_fs+0x14/0x80
> > >  ? vfs_kern_mount+0x67/0x170
> > >  ? do_mount+0x195/0xd00
> > >  ? kmem_cache_alloc_trace+0x231/0x2a0
> > >  ? SyS_mount+0x95/0xe0
> > >  ? entry_SYSCALL_64_fastpath+0x1f/0xbe
> > > 
> > > Any thoughts?  I'm not sure what's going on for sure, other than the
> > > call stack looks funny and it's midnight so I'm going to sleep. :)
> > > 
> > 
> > It looks like a problem with the loop in xfs_qm_dquot_walk(). The next
> > lookup index is calculated as:
> > 
> > 	 next_index = be32_to_cpu(dqp->q_core.d_id) + 1;
> > 
> > ... each time through the loop. With the uid written above, the +1
> > overflows the 32-bit next_index back to zero and the lookup starts over.
> > I suppose a simple fix might be to do something like the following.
> > Thoughts?
> > 
> > --- 8< ---
> > 
> > diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> > index 6ce948c..f013c893 100644
> > --- a/fs/xfs/xfs_qm.c
> > +++ b/fs/xfs/xfs_qm.c
> > @@ -111,6 +111,8 @@ xfs_qm_dquot_walk(
> >  			skipped = 0;
> >  			break;
> >  		}
> > +		if (!next_index)
> > +			break;
> 
> Well, this /does/ fix the quotacheck lockup... but leads me straight
> into the next problem, which is that xfs_quota -x -c 'report -i' just
> goes into an infinite loop:
> 
> root                3          0          0     00 [--------]
> #4294967295           1          0          0     00 [--------]
> <repeats>
> 
> That said, the userland APIs *chown/set*uid return -EINVAL if you pass
> in a userid of -1U, so one could argue that it's not a valid id anyway.
> Via stat(), the kernel squashes -1U down to 65534 (nobody), which
> implies that (Linux, anyway) doesn't consider -1U to be a valid id.
> ISTR XFS treats uids as a mostly opaque value that we get from and pass
> to the VFS without a whole lot of interpretation...?

Poking around in include/linux/uidgid.h, it seems that uid_valid()
thinks that -1U is not a valid user id, so perhaps the inode verifier
should chck for that.  Ditto for gid_valid().

But then there's project id -- xfs_quota won't let us set a projid of
4294967295, though I don't see anything in the kernel that prohibits
that.  chattr -p 4294967295 succeeds in setting the project id, which
means that we probably can't just ban it retroactively(??)

Thoughts?

--D

> 
> --D
> 
> >  	}
> >  
> >  	if (skipped) {
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html