Re: 6.5.0rc5 fs hang - ext4? raid?

Jens Axboe
2023-08-16T14:35:31Z

On 8/15/23 7:31 PM, Dr. David Alan Gilbert wrote:
> (Copying in Christoph and Jens)
>
> * Dr. David Alan Gilbert (dave@treblig.org) wrote:
>> * 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.
>
> I've just finished a bisect of this hang, and got to:
>
> 615939a2ae734e3e68c816d6749d1f5f79c62ab7 is the first bad commit
> commit 615939a2ae734e3e68c816d6749d1f5f79c62ab7
> Author: Christoph Hellwig <hch@lst.de>
> Date: Fri May 19 06:40:48 2023 +0200
>
> blk-mq: defer to the normal submission path for post-flush requests
>
> Requests with the FUA bit on hardware without FUA support need a post
> flush before returning to the caller, but they can still be sent using
> the normal I/O path after initializing the flush-related fields and
> end I/O handler.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
> Link: https://lore.kernel.org/r/20230519044050.107790-6-hch@lst.de
> Signed-off-by: Jens Axboe <axboe@kernel.dk>

Can you try and pull in:

https://git.kernel.dk/cgit/linux/commit/?h=block-6.5&id=5ff3213a5387e076af2b87f796f94b36965e8c3a

and see if that helps?

--
Jens Axboe