Re: [Qemu-stable] [PATCH v2 1/1] qemu-img: wait for convert coroutines to complete

[Anton Nefedov]

On 04/21/2017 03:37 PM, Peter Lieven wrote:
> Am 21.04.2017 um 14:19 schrieb Anton Nefedov:
> > On 04/21/2017 01:44 PM, Peter Lieven wrote:
> > > Am 21.04.2017 um 12:04 schrieb Anton Nefedov:
> > > > On error path (like i/o error in one of the coroutines), it's required to
> > > >   - wait for coroutines completion before cleaning the common structures
> > > >   - reenter dependent coroutines so they ever finish
> > > >
> > > > Introduced in 2d9187bc65.
> > > >
> > > > Signed-off-by: Anton Nefedov <address@hidden>
> > > > ---
> > > > [..]
> > >
> > >
> > > And what if we error out in the read path? Wouldn't be something like this 
> > > easier?
> > >
> > >
> > > diff --git a/qemu-img.c b/qemu-img.c
> > > index 22f559a..4ff1085 100644
> > > --- a/qemu-img.c
> > > +++ b/qemu-img.c
> > > @@ -1903,6 +1903,16 @@ static int convert_do_copy(ImgConvertState *s)
> > >          main_loop_wait(false);
> > >      }
> > >
> > > +    /* on error path we need to enter all coroutines that are still
> > > +     * running before cleaning up common structures */
> > > +    if (s->ret) {
> > > +        for (i = 0; i < s->num_coroutines; i++) {
> > > +             if (s->co[i]) {
> > > +                 qemu_coroutine_enter(s->co[i]);
> > > +             }
> > > +        }
> > > +    }
> > > +
> > >      if (s->compressed && !s->ret) {
> > >          /* signal EOF to align */
> > >          ret = blk_pwrite_compressed(s->target, 0, NULL, 0);
> > >
> > >
> > > Peter
> >
> > seemed a bit too daring to me to re-enter every coroutine potentially including 
> > the ones that yielded waiting for I/O completion.
> > If that's ok - that is for sure easier :)
>
> I think we should enter every coroutine that is still running and have it 
> terminate correctly. It was my mistake that I have not
> done this in the original patch. Can you check if the above fixes your test 
> cases that triggered the bug?

hi, sorry I'm late with the answer

this segfaults in bdrv_close(). Looks like it tries to finish some i/o 
which coroutine we have already entered and terminated?

(gdb) run
Starting program: /vz/anefedov/qemu-build/us/./qemu-img convert -O qcow2 
./harddisk.hdd.c ./harddisk.hdd
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7fffeac2d700 (LWP 436020)]
[New Thread 0x7fffe4ed6700 (LWP 436021)]
qemu-img: error while reading sector 20480: Input/output error
qemu-img: error while writing sector 19712: Operation now in progress

Program received signal SIGSEGV, Segmentation fault.
aio_co_wake (co=0x0) at /mnt/code/us-qemu/util/async.c:454
454         ctx = atomic_read(&co->ctx);
(gdb) bt
#0  aio_co_wake (co=0x0) at /mnt/code/us-qemu/util/async.c:454
/* [Anton]: thread_pool_co_cb () here */
#1  0x0000555555634629 in thread_pool_completion_bh 
(opaque=0x555555cfe020) at /mnt/code/us-qemu/util/thread-pool.c:189
#2  0x0000555555633b31 in aio_bh_call (bh=0x555555cfe0f0) at 
/mnt/code/us-qemu/util/async.c:90
#3  aio_bh_poll (address@hidden) at 
/mnt/code/us-qemu/util/async.c:118
#4  0x0000555555636f14 in aio_poll (address@hidden, 
blocking=<optimized out>) at /mnt/code/us-qemu/util/aio-posix.c:682
#5  0x00005555555c52d4 in bdrv_drain_recurse 
(address@hidden) at /mnt/code/us-qemu/block/io.c:164
#6  0x00005555555c5aed in bdrv_drained_begin 
(address@hidden) at /mnt/code/us-qemu/block/io.c:248
#7  0x0000555555581443 in bdrv_close (bs=0x555555d22560) at 
/mnt/code/us-qemu/block.c:2909
#8  bdrv_delete (bs=0x555555d22560) at /mnt/code/us-qemu/block.c:3100
#9  bdrv_unref (bs=0x555555d22560) at /mnt/code/us-qemu/block.c:4087
#10 0x00005555555baf44 in blk_remove_bs (address@hidden) 
at /mnt/code/us-qemu/block/block-backend.c:552
#11 0x00005555555bb173 in blk_delete (blk=0x555555d22380) at 
/mnt/code/us-qemu/block/block-backend.c:238
#12 blk_unref (address@hidden) at 
/mnt/code/us-qemu/block/block-backend.c:282
#13 0x000055555557a22c in img_convert (argc=<optimized out>, 
argv=<optimized out>) at /mnt/code/us-qemu/qemu-img.c:2359
#14 0x0000555555574189 in main (argc=5, argv=0x7fffffffe4a0) at 
/mnt/code/us-qemu/qemu-img.c:4464


> Peter

/Anton