Re: 6.5.0rc5 fs hang - ext4? raid?

Dr. David Alan Gilbert
2023-08-15T17:51:26Z

* Dr. David Alan Gilbert (dave@treblig.org) wrote:
> * Theodore Ts'o (tytso@mit.edu) wrote:
> > On Mon, Aug 14, 2023 at 09:02:53PM +0000, Dr. David Alan Gilbert wrote:
> > > dg 29594 29592 0 18:40 pts/0 00:00:00 /usr/bin/ar --plugin /usr/libexec/gcc/x86_64-redhat-linux/13/liblto_plugin.so -csrDT src/intel/perf/libintel_perf.a src/intel/perf/libintel_perf.a.p/meson-generated_.._intel_perf_metrics.c.o src/intel/perf/libintel_perf.a.p/intel_perf.c.o src/intel/perf/libintel_perf.a.p/intel_perf_query.c.o src/intel/perf/libintel_perf.a.p/intel_perf_mdapi.c.o
> > >
> > > [root@dalek dg]# cat /proc/29594/stack
> > > [<0>] md_super_wait+0xa2/0xe0
> > > [<0>] md_bitmap_unplug+0xd2/0x120
> > > [<0>] flush_bio_list+0xf3/0x100 [raid1]
> > > [<0>] raid1_unplug+0x3b/0xb0 [raid1]
> > > [<0>] __blk_flush_plug+0xd7/0x150
> > > [<0>] blk_finish_plug+0x29/0x40
> > > [<0>] ext4_do_writepages+0x401/0xc90
> > > [<0>] ext4_writepages+0xad/0x180
> >
> > If you want a few seconds and try grabbing cat /proc/29594/stack
> > again, what does the stack trace stay consistent as above?
>
> I'll get back to that and retry it.

Yeh, the stack is consistent; this time around it's an 'ar' in a kernel
build:

[root@dalek dg]# cat /proc/17970/stack
[<0>] md_super_wait+0xa2/0xe0
[<0>] md_bitmap_unplug+0xad/0x120
[<0>] flush_bio_list+0xf3/0x100 [raid1]
[<0>] raid1_unplug+0x3b/0xb0 [raid1]
[<0>] __blk_flush_plug+0xd7/0x150
[<0>] blk_finish_plug+0x29/0x40
[<0>] ext4_do_writepages+0x401/0xc90
[<0>] ext4_writepages+0xad/0x180
[<0>] do_writepages+0xd2/0x1e0
[<0>] filemap_fdatawrite_wbc+0x63/0x90
[<0>] __filemap_fdatawrite_range+0x5c/0x80
[<0>] ext4_release_file+0x74/0xb0
[<0>] __fput+0xf5/0x2a0
[<0>] task_work_run+0x5d/0x90
[<0>] exit_to_user_mode_prepare+0x1e6/0x1f0
[<0>] syscall_exit_to_user_mode+0x1b/0x40
[<0>] do_syscall_64+0x6c/0x90
[<0>] entry_SYSCALL_64_after_hwframe+0x6e/0xd8
[root@dalek dg]# cat /proc/17970/stack
[<0>] md_super_wait+0xa2/0xe0
[<0>] md_bitmap_unplug+0xad/0x120
[<0>] flush_bio_list+0xf3/0x100 [raid1]
[<0>] raid1_unplug+0x3b/0xb0 [raid1]
[<0>] __blk_flush_plug+0xd7/0x150
[<0>] blk_finish_plug+0x29/0x40
[<0>] ext4_do_writepages+0x401/0xc90
[<0>] ext4_writepages+0xad/0x180
[<0>] do_writepages+0xd2/0x1e0
[<0>] filemap_fdatawrite_wbc+0x63/0x90
[<0>] __filemap_fdatawrite_range+0x5c/0x80
[<0>] ext4_release_file+0x74/0xb0
[<0>] __fput+0xf5/0x2a0
[<0>] task_work_run+0x5d/0x90
[<0>] exit_to_user_mode_prepare+0x1e6/0x1f0
[<0>] syscall_exit_to_user_mode+0x1b/0x40
[<0>] do_syscall_64+0x6c/0x90
[<0>] entry_SYSCALL_64_after_hwframe+0x6e/0xd8

> > Also, if you have iostat installed (usually part of the sysstat
> > package), does "iostat 1" show any I/O activity on the md device?

iostat is showing something odd, most devices are at 0,
except for 3 of the dm's that are stuck at 100% utilisation with
apparently nothing going on:

avg-cpu: %user %nice %system %iowait %steal %idle
0.06 0.00 0.03 53.06 0.00 46.84

Device r/s rkB/s rrqm/s %rrqm r_await rareq-sz w/s wkB/s wrqm/s %wrqm w_await wareq-sz d/s dkB/s drqm/s %drqm d_await dareq-sz f/s f_await aqu-sz %util
...
dm-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
dm-17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
dm-18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
dm-19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
dm-2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
dm-20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
....

dm-20 is the /dev/mapper/main-more which is the RAID on which the
fs runs, 16 and 17 are main-more_rmeta_0 and main-more_rimage_0
so something screwy is going on there.

Dave

> > What about the underying block dvices used by the md device? If the
> > md device is attached to HDD's where you can see the activity light,
> > can you see (or hear) any disk activity?
>
> It's spinning rust, and I hear them go quiet when the hang happens.
>
> Dave
>
> > This sure seems like either the I/O driver isn't processing requests,
> > or some kind of hang in the md layer....
> >
> > - Ted
> --
> -----Open up your eyes, open up your mind, open up your code -------
> / Dr. David Alan Gilbert | Running GNU/Linux | Happy \
> \ dave @ treblig.org | | In Hex /
> \ _________________________|_____ http://www.treblig.org |_______/
--
-----Open up your eyes, open up your mind, open up your code -------
/ Dr. David Alan Gilbert | Running GNU/Linux | Happy \
\ dave @ treblig.org | | In Hex /
\ _________________________|_____ http://www.treblig.org |_______/