Re: v5.10.1 xfs deadlock

[Donald Buczek]

On 18.12.20 22:49, Dave Chinner wrote:
> On Thu, Dec 17, 2020 at 06:44:51PM +0100, Donald Buczek wrote:
> > Dear xfs developer,
> >
> > I was doing some testing on a Linux 5.10.1 system with two 100 TB xfs filesystems on md raid6 raids.
> >
> > The stress test was essentially `cp -a`ing a Linux source repository with two threads in parallel on each filesystem.
> >
> > After about on hour, the processes to one filesystem (md1) blocked, 30 minutes later the process to the other filesystem (md0) did.
> >
> >      root      7322  2167  0 Dec16 pts/1    00:00:06 cp -a /jbod/M8068/scratch/linux /jbod/M8068/scratch/1/linux.018.TMP
> >      root      7329  2169  0 Dec16 pts/1    00:00:05 cp -a /jbod/M8068/scratch/linux /jbod/M8068/scratch/2/linux.019.TMP
> >      root     13856  2170  0 Dec16 pts/1    00:00:08 cp -a /jbod/M8067/scratch/linux /jbod/M8067/scratch/2/linux.028.TMP
> >      root     13899  2168  0 Dec16 pts/1    00:00:05 cp -a /jbod/M8067/scratch/linux /jbod/M8067/scratch/1/linux.027.TMP
> >
> > Some info from the system (all stack traces, slabinfo) is available here: https://owww.molgen.mpg.de/~buczek/2020-12-16.info.txt
> >
> > It stands out, that there are many (549 for md0, but only 10 for md1)  "xfs-conv" threads all with stacks like this
> >
> >      [<0>] xfs_log_commit_cil+0x6cc/0x7c0
> >      [<0>] __xfs_trans_commit+0xab/0x320
> >      [<0>] xfs_iomap_write_unwritten+0xcb/0x2e0
> >      [<0>] xfs_end_ioend+0xc6/0x110
> >      [<0>] xfs_end_io+0xad/0xe0
> >      [<0>] process_one_work+0x1dd/0x3e0
> >      [<0>] worker_thread+0x2d/0x3b0
> >      [<0>] kthread+0x118/0x130
> >      [<0>] ret_from_fork+0x22/0x30
> >
> > xfs_log_commit_cil+0x6cc is
> >
> >    xfs_log_commit_cil()
> >      xlog_cil_push_background(log)
> >        xlog_wait(&cil->xc_push_wait, &cil->xc_push_lock);
> >
> > Some other threads, including the four "cp" commands are also blocking at xfs_log_commit_cil+0x6cc
> >
> > There are also single "flush" process for each md device with this stack signature:
> >
> >      [<0>] xfs_map_blocks+0xbf/0x400
> >      [<0>] iomap_do_writepage+0x15e/0x880
> >      [<0>] write_cache_pages+0x175/0x3f0
> >      [<0>] iomap_writepages+0x1c/0x40
> >      [<0>] xfs_vm_writepages+0x59/0x80
> >      [<0>] do_writepages+0x4b/0xe0
> >      [<0>] __writeback_single_inode+0x42/0x300
> >      [<0>] writeback_sb_inodes+0x198/0x3f0
> >      [<0>] __writeback_inodes_wb+0x5e/0xc0
> >      [<0>] wb_writeback+0x246/0x2d0
> >      [<0>] wb_workfn+0x26e/0x490
> >      [<0>] process_one_work+0x1dd/0x3e0
> >      [<0>] worker_thread+0x2d/0x3b0
> >      [<0>] kthread+0x118/0x130
> >      [<0>] ret_from_fork+0x22/0x30
> >
> > xfs_map_blocks+0xbf is the
> >
> >      xfs_ilock(ip, XFS_ILOCK_SHARED);
> >
> > in xfs_map_blocks().
>
> Can you post the entire dmesg output after running
> 'echo w > /proc/sysrq-trigger' to dump all the block threads to
> dmesg?
>
> > I have an out of tree driver for the HBA ( smartpqi 2.1.6-005
> > pulled from linux-scsi) , but it is unlikely that this blocking is
> > related to that, because the md block devices itself are
> > responsive (`xxd /dev/md0` )
>
> My bet is that the OOT driver/hardware had dropped a log IO on the
> floor - XFS is waiting for the CIL push to complete, and I'm betting
> that is stuck waiting for iclog IO completion while writing the CIL
> to the journal. The sysrq output will tell us if this is the case,
> so that's the first place to look.

I think you are right here, and I'm sorry for blaming the wrong layer.

I've got the system into another (though little different) zero-progress situation. This time it happened on md0 only while md1 was still working.

I think, this should be prove, that the failure is on the block layer of the member disks:

    root:deadbird:/scratch/local/# for f in /sys/devices/virtual/block/md?/md/rd*/block/inflight;do echo $f: $(cat $f);done
    /sys/devices/virtual/block/md0/md/rd0/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd1/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd10/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd11/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd12/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd13/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd14/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd15/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd2/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd3/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd4/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd5/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd6/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd7/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd8/block/inflight: 1 0
    /sys/devices/virtual/block/md0/md/rd9/block/inflight: 1 0
    /sys/devices/virtual/block/md1/md/rd0/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd1/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd10/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd11/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd12/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd13/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd14/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd15/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd2/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd3/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd4/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd5/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd6/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd7/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd8/block/inflight: 0 0
    /sys/devices/virtual/block/md1/md/rd9/block/inflight: 0 0

Best

  Donald

> Cheers,
>
> Dave.
--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433