> On March 31, 2020 5:37 PM Kevin Wolf <kw...@redhat.com> wrote:
>
>
> Am 31.03.2020 um 17:24 hat Dietmar Maurer geschrieben:
> >
> > > > How can I see/debug those waiting request?
> > >
> > > Examine bs->tracked_requests list.
> > >
> > > BdrvTrackedRequest has "Coroutine *co" field. It's a pointer of coroutine
> > > of this request. You may use qemu-gdb script to print request's coroutine
> > > back-trace:
> >
> > I would, but there are no tracked request at all.
> >
> > print bs->tracked_requests
> > $2 = {lh_first = 0x0}
>
> Then it's one of the recursively checked parents, as you already figured
> out.
>
> > Looks bdrv_parent_drained_poll_single() calls
> > blk_root_drained_poll(), which return true in my case (in_flight > 5).
>
> Can you identify which BlockBackend is this? Specifically if it's the
> one attached to a guest device or whether it belongs to the block job.
This can trigger from various different places, but the simplest case is when
its called from drive_backup_prepare
> bdrv_drained_begin(bs);
which is the backup source drive.
Note: I have added printf debug statement to the source, so the line numbers
may not exactly match
#0 0x00007ffff5cb3916 in __GI_ppoll (fds=0x7fff63d30c40, nfds=2,
timeout=<optimized out>, timeout@entry=0x0, sigmask=sigmask@entry=0x0)
at ../sysdeps/unix/sysv/linux/ppoll.c:39
#1 0x0000555555c60479 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized
out>, __fds=<optimized out>) at /usr/include/x86_64-linux-gnu/bits/poll2.h:77
#2 0x0000555555c60479 in qemu_poll_ns (fds=<optimized out>, nfds=<optimized
out>, timeout=timeout@entry=-1) at util/qemu-timer.c:335
#3 0x0000555555c62c61 in fdmon_poll_wait (ctx=0x7fffe8905e80,
ready_list=0x7fffffffda68, timeout=-1) at util/fdmon-poll.c:79
#4 0x0000555555c62247 in aio_poll (ctx=0x7fffe8905e80,
blocking=blocking@entry=true) at util/aio-posix.c:589
#5 0x0000555555bc25d5 in bdrv_do_drained_begin (poll=<optimized out>,
ignore_bds_parents=false, parent=0x0, recursive=false, bs=0x7fffe8954bc0)
at block/io.c:430
#6 0x0000555555bc25d5 in bdrv_do_drained_begin
(bs=0x7fffe8954bc0, recursive=<optimized out>, parent=0x0,
ignore_bds_parents=<optimized out>, poll=<optimized out>) at block/io.c:395
#7 0x000055555595f753 in drive_backup_prepare (common=0x7fffe560c200,
errp=0x7fffffffdba8) at blockdev.c:1759
#8 0x0000555555961f0a in qmp_transaction
(dev_list=dev_list@entry=0x7fffffffdc20, has_props=has_props@entry=false,
props=0x7fffe560e0e0,
props@entry=0x0, errp=errp@entry=0x7fffffffdc58) at blockdev.c:2406
#9 0x00005555559633c2 in blockdev_do_action (errp=0x7fffffffdc58,
action=0x7fffffffdc10) at blockdev.c:1054
#10 0x00005555559633c2 in qmp_drive_backup (backup=backup@entry=0x7fffffffdc60,
errp=errp@entry=0x7fffffffdc58) at blockdev.c:3134
#11 0x0000555555b1e1d1 in qmp_marshal_drive_backup (args=<optimized out>,
ret=<optimized out>, errp=0x7fffffffdd38) at qapi/qapi-commands-block-core.c:555
#12 0x0000555555c15b08 in qmp_dispatch (cmds=0x555556162000 <qmp_commands>,
request=<optimized out>, allow_oob=<optimized out>) at qapi/qmp-dispatch.c:155
#13 0x0000555555affca1 in monitor_qmp_dispatch (mon=0x7fffe8915d80,
req=<optimized out>) at monitor/qmp.c:145
#14 0x0000555555b0048a in monitor_qmp_bh_dispatcher (data=<optimized out>) at
monitor/qmp.c:234
#15 0x0000555555c5e9d5 in aio_bh_call (bh=0x7fffe8e8f960) at util/async.c:164
#16 0x0000555555c5e9d5 in aio_bh_poll (ctx=ctx@entry=0x7fffe8f3ef80) at
util/async.c:164
#17 0x0000555555c6208e in aio_dispatch (ctx=0x7fffe8f3ef80) at
util/aio-posix.c:380
#18 0x0000555555c5e8be in aio_ctx_dispatch (source=<optimized out>,
callback=<optimized out>, user_data=<optimized out>) at util/async.c:298
#19 0x00007ffff7c7ef2e in g_main_context_dispatch () at
/usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#20 0x0000555555c612f8 in glib_pollfds_poll () at util/main-loop.c:219
#21 0x0000555555c612f8 in os_host_main_loop_wait (timeout=<optimized out>) at
util/main-loop.c:242
#22 0x0000555555c612f8 in main_loop_wait (nonblocking=nonblocking@entry=0) at
util/main-loop.c:518
#23 0x00005555558fc5a9 in qemu_main_loop () at
/home/dietmar/pve5-devel/mirror_qemu/softmmu/vl.c:1665
#24 0x0000555555800c3e in main (argc=<optimized out>, argv=<optimized out>,
envp=<optimized out>) at /home/dietmar/pve5-devel/mirror_qemu/softmmu/main.c:49
>
> Maybe have a look at the job coroutine, too. You can probably easiest
> find it in the 'jobs' list, and then print the coroutine backtrace for
> job->co.
There is in drive_backup_prepare(), before the job gets created.
> > Looks like I am loosing poll events somewhere?
>
> I don't think we've lost any event if in_flight > 0. It means that
> something is still supposedly active. Maybe the job deadlocked.
This is a simple call to bdrv_drained_begin(bs) (before we setup the job).
I really nobody else able to reproduce this (somebody already tried to
reproduce)?
