On Thu, Apr 27, 2023 at 04:36:14PM +0200, Juan Quintela wrote: > Fiona Ebner <f.eb...@proxmox.com> wrote: > > Am 27.04.23 um 13:03 schrieb Kevin Wolf: > >> Am 26.04.2023 um 16:31 hat Fiona Ebner geschrieben: > >>> Am 20.04.23 um 08:55 schrieb Paolo Bonzini: > > Hi > > > Our function is a custom variant of saving a snapshot and uses > > qemu_savevm_state_setup(), which is why the qemu_mutex_unlock_iothread() > > is there. I looked for inspiration for how upstream does things and it > > turns out that upstream QEMU v8.0.0 has essentially the same issue with > > snapshot-save. When snapshot_save_job_bh runs in a vCPU thread instead > > of the main thread, the situation is the same: after > > qemu_mutex_unlock_iothread(), qemu_get_current_aio_context() will return > > 0x0 and then the assertion in the AIO_WAIT_WHILE_INTERNAL macro fails > > (this time the generated coroutine wrapper is bdrv_writev_vmstate)[0]. > > > > > > So all bottom halves scheduled for the main thread's AioContext can > > potentially get to run in a vCPU thread and need to be very careful with > > things like qemu_mutex_unlock_iothread. > > > > Is qemu_get_current_aio_context() returning 0x0 expected? I haven't > > looked into why it happens yet. Does there need to be a way to drop the > > BQL without also giving up the main thread's AioContext or would it be > > enough to re-acquire the context? > > > > CC-ing Juan as the migration maintainer. > > This is the world backwards. > The tradition is that migration people blame block layer people for > breaking things and for help, not the other way around O:-) > > > Best Regards, > > Fiona > > > > [0]: > >> Thread 21 "CPU 0/KVM" received signal SIGABRT, Aborted. > >> __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 > >> 50 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory. > >> (gdb) bt > >> #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 > >> #1 0x00007f9027b3e537 in __GI_abort () at abort.c:79 > >> #2 0x00007f9027b3e40f in __assert_fail_base (fmt=0x7f9027cb66a8 > >> "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", > >> assertion=0x558ed44fcec0 "qemu_get_current_aio_context() == > >> qemu_get_aio_context()", file=0x558ed44fce80 > >> "/home/febner/repos/qemu/block/block-gen.h", line=43, > >> function=<optimized out>) at assert.c:92 > >> #3 0x00007f9027b4d662 in __GI___assert_fail > >> (assertion=0x558ed44fcec0 "qemu_get_current_aio_context() == > >> qemu_get_aio_context()", file=0x558ed44fce80 > >> "/home/febner/repos/qemu/block/block-gen.h", line=43, > >> function=0x558ed44fcf80 <__PRETTY_FUNCTION__.14> "bdrv_poll_co") at > >> assert.c:101 > >> #4 0x0000558ed412df5f in bdrv_poll_co (s=0x7f8ffcff37a0) at > >> /home/febner/repos/qemu/block/block-gen.h:43 > >> #5 0x0000558ed412f4cd in bdrv_writev_vmstate (bs=0x558ed60536a0, > >> qiov=0x7f8ffcff3840, pos=0) at block/block-gen.c:809 > >> #6 0x0000558ed3df36d0 in qio_channel_block_writev > >> (ioc=0x7f8ff40ac060, iov=0x7f8ff43f6350, niov=1, fds=0x0, nfds=0, > >> flags=0, errp=0x7f8ffcff39c0) at ../migration/channel-block.c:89 > >> #7 0x0000558ed40feedb in qio_channel_writev_full > >> (ioc=0x7f8ff40ac060, iov=0x7f8ff43f6350, niov=1, fds=0x0, nfds=0, > >> flags=0, errp=0x7f8ffcff39c0) at ../io/channel.c:108 > >> #8 0x0000558ed40ff3c3 in qio_channel_writev_full_all > >> (ioc=0x7f8ff40ac060, iov=0x7f8ff4648040, niov=1, fds=0x0, nfds=0, > >> flags=0, errp=0x7f8ffcff39c0) at ../io/channel.c:263 > >> #9 0x0000558ed40ff2e4 in qio_channel_writev_all (ioc=0x7f8ff40ac060, > >> iov=0x7f8ff4648040, niov=1, errp=0x7f8ffcff39c0) at > >> ../io/channel.c:242 > >> #10 0x0000558ed3dee4dc in qemu_fflush (f=0x7f8ff4640000) at > >> ../migration/qemu-file.c:302 > >> #11 0x0000558ed4050f91 in ram_save_setup (f=0x7f8ff4640000, > >> opaque=0x558ed4ca34c0 <ram_state>) at ../migration/ram.c:3302 > >> #12 0x0000558ed3e141c8 in qemu_savevm_state_setup (f=0x7f8ff4640000) at > >> ../migration/savevm.c:1266 > >> #13 0x0000558ed3e14eed in qemu_savevm_state (f=0x7f8ff4640000, > >> errp=0x558ed68c5238) at ../migration/savevm.c:1626 > >> #14 0x0000558ed3e1755e in save_snapshot (name=0x558ed72af790 > >> "snap0", overwrite=false, vmstate=0x558ed6708ce0 "scsi0", > >> has_devices=true, devices=0x558ed66d6a60, errp=0x558ed68c5238) at > >> ../migration/savevm.c:2954 > >> #15 0x0000558ed3e17fb1 in snapshot_save_job_bh (opaque=0x558ed68c5170) at > >> ../migration/savevm.c:3253 > >> #16 0x0000558ed42f050a in aio_bh_call (bh=0x558ed671ae00) at > >> ../util/async.c:155 > >> #17 0x0000558ed42f0615 in aio_bh_poll (ctx=0x558ed5c62910) at > >> ../util/async.c:184 > >> #18 0x0000558ed42d47b8 in aio_poll (ctx=0x558ed5c62910, blocking=true) at > >> ../util/aio-posix.c:721 > >> #19 0x0000558ed412df1c in bdrv_poll_co (s=0x7f8ffcff3eb0) at > >> /home/febner/repos/qemu/block/block-gen.h:43 > >> #20 0x0000558ed4130c3a in blk_pwrite (blk=0x558ed5ed4f60, > >> offset=230912, bytes=512, buf=0x7f8ffc438600, flags=0) at > >> block/block-gen.c:1650 > >> #21 0x0000558ed3ba9078 in pflash_update (pfl=0x558ed5eb7b30, > >> offset=230912, size=1) at ../hw/block/pflash_cfi01.c:394 > >> #22 0x0000558ed3ba9749 in pflash_write (pfl=0x558ed5eb7b30, > >> offset=231232, value=0, width=1, be=0) at > >> ../hw/block/pflash_cfi01.c:522 > >> #23 0x0000558ed3ba9cda in pflash_mem_write_with_attrs > >> (opaque=0x558ed5eb7b30, addr=231232, value=0, len=1, attrs=...) at > >> ../hw/block/pflash_cfi01.c:681 > >> #24 0x0000558ed402a36a in memory_region_write_with_attrs_accessor > >> (mr=0x558ed5eb7ef0, addr=231232, value=0x7f8ffcff40c8, size=1, > >> shift=0, mask=255, attrs=...) at ../softmmu/memory.c:514 > >> #25 0x0000558ed402a4a9 in access_with_adjusted_size (addr=231232, > >> value=0x7f8ffcff40c8, size=1, access_size_min=1, access_size_max=4, > >> access_fn=0x558ed402a270 <memory_region_write_with_attrs_accessor>, > >> mr=0x558ed5eb7ef0, attrs=...) at ../softmmu/memory.c:555 > >> #26 0x0000558ed402d5de in memory_region_dispatch_write > >> (mr=0x558ed5eb7ef0, addr=231232, data=0, op=MO_8, attrs=...) at > >> ../softmmu/memory.c:1522 > >> #27 0x0000558ed403a6f4 in flatview_write_continue > >> (fv=0x558ed66d62c0, addr=4291004224, attrs=..., ptr=0x7f9029957028, > >> len=1, addr1=231232, l=1, mr=0x558ed5eb7ef0) at > >> ../softmmu/physmem.c:2641 > >> #28 0x0000558ed403a857 in flatview_write (fv=0x558ed66d62c0, > >> addr=4291004224, attrs=..., buf=0x7f9029957028, len=1) at > >> ../softmmu/physmem.c:2683 > >> #29 0x0000558ed403ac07 in address_space_write (as=0x558ed4ca2b20 > >> <address_space_memory>, addr=4291004224, attrs=..., > >> buf=0x7f9029957028, len=1) at ../softmmu/physmem.c:2779 > >> #30 0x0000558ed403ac74 in address_space_rw (as=0x558ed4ca2b20 > >> <address_space_memory>, addr=4291004224, attrs=..., > >> buf=0x7f9029957028, len=1, is_write=true) at > >> ../softmmu/physmem.c:2789 > >> #31 0x0000558ed40cea88 in kvm_cpu_exec (cpu=0x558ed622a910) at > >> ../accel/kvm/kvm-all.c:2989 > >> #32 0x0000558ed40d179a in kvm_vcpu_thread_fn (arg=0x558ed622a910) at > >> ../accel/kvm/kvm-accel-ops.c:51 > >> #33 0x0000558ed42d925f in qemu_thread_start (args=0x558ed5c68c80) at > >> ../util/qemu-thread-posix.c:541 > >> #34 0x00007f9028ab7ea7 in start_thread (arg=<optimized out>) at > >> pthread_create.c:477 > >> #35 0x00007f9027c18a2f in clone () at > >> ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
Totally unfamiliar with block jobs, but... does it mean that snapshot_*_job_bh()s should just always make sure BQL taken? Thanks, -- Peter Xu
