Re: backup transaction with io-thread core dumps

[John Snow]

Well, that was a rollercoaster of emotions as I read your mails.

On 3/24/20 9:33 AM, Dietmar Maurer wrote:
> spoke too soon - the error is still there, sigh
>  
>> This is fixed with this patch:
>>
>> https://lists.gnu.org/archive/html/qemu-devel/2020-03/msg07249.html
>>
>> thanks!
>>
>>> On March 24, 2020 12:13 PM Dietmar Maurer <address@hidden> wrote:
>>>
>>>  
>>> I get a core dump with backup transactions when using io-threads.
>>>
>>> To reproduce, create and start a VM with:
>>>
>>> # qemu-img create disk1.raw 100M
>>> # qemu-img create disk2.raw 100M
>>> #./x86_64-softmmu/qemu-system-x86_64 -chardev 
>>> 'socket,id=qmp,path=/var/run/qemu-test.qmp,server,nowait' -mon 
>>> 'chardev=qmp,mode=control' -pidfile /var/run/qemu-server/108.pid  -m 512 
>>> -object 'iothread,id=iothread-virtioscsi0' -object 
>>> 'iothread,id=iothread-virtioscsi1'  -device 
>>> 'virtio-scsi-pci,id=virtioscsi0,iothread=iothread-virtioscsi0' -drive 
>>> 'file=disk1.raw,if=none,id=drive-scsi0,format=raw,cache=none,aio=native,detect-zeroes=on'
>>>  -device 
>>> 'scsi-hd,bus=virtioscsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0'
>>>  -device 'virtio-scsi-pci,id=virtioscsi1,iothread=iothread-virtioscsi1' 
>>> -drive 
>>> 'file=disk2.raw,if=none,id=drive-scsi1,format=raw,cache=none,aio=native,detect-zeroes=on'
>>>  -device 
>>> 'scsi-hd,bus=virtioscsi1.0,channel=0,scsi-id=0,lun=1,drive=drive-scsi1,id=scsi1'
>>>
>>> Then open socat to the qmp socket
>>> # socat /var/run/qemu-test.qmp -
>>>
>>> And run the following qmp command:
>>>
>>> { "execute": "qmp_capabilities", "arguments": {} }
>>> { "execute": "transaction", "arguments":  { "actions": [{ "type": 
>>> "drive-backup", "data": { "device": "drive-scsi0", "sync": "full", 
>>> "target": "backup-sysi0.raw" }}, { "type": "drive-backup", "data": { 
>>> "device": "drive-scsi1", "sync": "full", "target": "backup-scsi1.raw" }}], 
>>> "properties": { "completion-mode": "grouped" } } }
>>>
>>> The VM will core dump:
>>>
>>> qemu: qemu_mutex_unlock_impl: Operation not permitted
>>> Aborted (core dumped)
>>> (gdb) bt
>>> #0  0x00007f099d5037bb in __GI_raise (sig=sig@entry=6) at 
>>> ../sysdeps/unix/sysv/linux/raise.c:50
>>> #1  0x00007f099d4ee535 in __GI_abort () at abort.c:79
>>> #2  0x000055c04e39525e in error_exit (err=<optimized out>, 
>>> msg=msg@entry=0x55c04e5122e0 <__func__.16544> "qemu_mutex_unlock_impl") at 
>>> util/qemu-thread-posix.c:36
>>> #3  0x000055c04e395813 in qemu_mutex_unlock_impl 
>>> (mutex=mutex@entry=0x7f09903154e0, file=file@entry=0x55c04e51129f 
>>> "util/async.c", line=line@entry=601)
>>>     at util/qemu-thread-posix.c:108
>>> #4  0x000055c04e38f8e5 in aio_context_release 
>>> (ctx=ctx@entry=0x7f0990315480) at util/async.c:601
>>> #5  0x000055c04e299073 in bdrv_set_aio_context_ignore (bs=0x7f0929a76500, 
>>> new_context=new_context@entry=0x7f0990315000, 
>>> ignore=ignore@entry=0x7ffe08fa7400)
>>>     at block.c:6238
>>> #6  0x000055c04e2990cc in bdrv_set_aio_context_ignore 
>>> (bs=bs@entry=0x7f092af47900, new_context=new_context@entry=0x7f0990315000, 
>>> ignore=ignore@entry=0x7ffe08fa7400)
>>>     at block.c:6211
>>> #7  0x000055c04e299443 in bdrv_child_try_set_aio_context 
>>> (bs=bs@entry=0x7f092af47900, ctx=0x7f0990315000, 
>>> ignore_child=ignore_child@entry=0x0, errp=errp@entry=0x0)
>>>     at block.c:6324
>>> #8  0x000055c04e299576 in bdrv_try_set_aio_context (errp=0x0, 
>>> ctx=<optimized out>, bs=0x7f092af47900) at block.c:6333
>>> #9  0x000055c04e299576 in bdrv_replace_child 
>>> (child=child@entry=0x7f09902ef5e0, new_bs=new_bs@entry=0x0) at block.c:2551
>>> #10 0x000055c04e2995ff in bdrv_detach_child (child=0x7f09902ef5e0) at 
>>> block.c:2666
>>> #11 0x000055c04e299ec9 in bdrv_root_unref_child (child=<optimized out>) at 
>>> block.c:2677
>>> #12 0x000055c04e29f3fe in block_job_remove_all_bdrv 
>>> (job=job@entry=0x7f0927c18800) at blockjob.c:191
>>> #13 0x000055c04e29f429 in block_job_free (job=0x7f0927c18800) at 
>>> blockjob.c:88
>>> #14 0x000055c04e2a0909 in job_unref (job=0x7f0927c18800) at job.c:359
>>> #15 0x000055c04e2a0909 in job_unref (job=0x7f0927c18800) at job.c:351
>>> #16 0x000055c04e2a0b68 in job_conclude (job=0x7f0927c18800) at job.c:620
>>> #17 0x000055c04e2a0b68 in job_finalize_single (job=0x7f0927c18800) at 
>>> job.c:688
>>> #18 0x000055c04e2a0b68 in job_finalize_single (job=0x7f0927c18800) at 
>>> job.c:660
>>> #19 0x000055c04e2a14fc in job_txn_apply (txn=<optimized out>, 
>>> fn=0x55c04e2a0a50 <job_finalize_single>) at job.c:145
>>> #20 0x000055c04e2a14fc in job_do_finalize (job=0x7f0927c1c200) at job.c:781
>>> #21 0x000055c04e2a1751 in job_completed_txn_success (job=0x7f0927c1c200) at 
>>> job.c:831
>>> #22 0x000055c04e2a1751 in job_completed (job=0x7f0927c1c200) at job.c:844
>>> #23 0x000055c04e2a1751 in job_completed (job=0x7f0927c1c200) at job.c:835
>>> #24 0x000055c04e2a17b0 in job_exit (opaque=0x7f0927c1c200) at job.c:863
>>> #25 0x000055c04e38ee75 in aio_bh_call (bh=0x7f098ec52000) at 
>>> util/async.c:164
>>> #26 0x000055c04e38ee75 in aio_bh_poll (ctx=ctx@entry=0x7f0990315000) at 
>>> util/async.c:164
>>> #27 0x000055c04e3924fe in aio_dispatch (ctx=0x7f0990315000) at 
>>> util/aio-posix.c:380
>>> #28 0x000055c04e38ed5e in aio_ctx_dispatch (source=<optimized out>, 
>>> callback=<optimized out>, user_data=<optimized out>) at util/async.c:298
>>> #29 0x00007f099f020f2e in g_main_context_dispatch () at 
>>> /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
>>> #30 0x000055c04e391768 in glib_pollfds_poll () at util/main-loop.c:219
>>> #31 0x000055c04e391768 in os_host_main_loop_wait (timeout=<optimized out>) 
>>> at util/main-loop.c:242
>>> #32 0x000055c04e391768 in main_loop_wait (nonblocking=nonblocking@entry=0) 
>>> at util/main-loop.c:518
>>> #33 0x000055c04e032329 in qemu_main_loop () at 
>>> /home/dietmar/pve5-devel/mirror_qemu/softmmu/vl.c:1665
>>> #34 0x000055c04df36a8e in main (argc=<optimized out>, argv=<optimized out>, 
>>> envp=<optimized out>) at 
>>> /home/dietmar/pve5-devel/mirror_qemu/softmmu/main.c:49
> 

Alright, let's start the field autopsy.

What version of QEMU are you running? Sergio contributed a lot of AIO
context (and iothread) fixes this release; this looks (at a glance) to
be similar and related.

If you are running 4.2 and not the latest HEAD, it's a strong candidate.

Check this out:
https://lists.gnu.org/archive/html/qemu-devel/2020-01/msg01440.html

hth,
--js