blk_root_drained_end is not thread-safe too. I started looking at that with https://www.mail-archive.com/[email protected]/msg925670.html; that's certainly a prerequisite for this patch to be a full fix, but I have not checked if it's enough because I don't have the QEMU sources at hand right now.
Paolo Il mer 4 gen 2023, 20:56 Stefan Hajnoczi <[email protected]> ha scritto: > scsi_device_purge_requests() is called from I/O code by virtio-scsi TMF > emulation code. It must not call Global State APIs like blk_drain() > because that results in an assertion failure. > > blk_drain() is a Global State API because it uses bdrv_unref(). Actually > ref/unref is unnecessary in device emulation code because the drive= > qdev property holds the reference. > > Introduce blk_drain_noref(), a variant of blk_drain() that is > IO_OR_GS_CODE() and doesn't take a reference to the BlockBackend. > > This fixes the following virtio-scsi IOThread assertion failure when > hot-plugging scsi-hd devices: > > qemu-kvm: ../block/block-backend.c:1780: void blk_drain(BlockBackend *): > Assertion `qemu_in_main_thread()' failed. > > #0 0x00007f4b6a0a154c __pthread_kill_implementation (libc.so.6> > #1 0x00007f4b6a054d46 raise (libc.so.6 + 0x54d46) > #2 0x00007f4b6a0287f3 abort (libc.so.6 + 0x287f3) > #3 0x00007f4b6a02871b __assert_fail_base.cold (libc.so.6 + 0x2> > #4 0x00007f4b6a04dce6 __assert_fail (libc.so.6 + 0x4dce6) > #5 0x000055c811253ac0 blk_drain (qemu-kvm + 0x808ac0) > #6 0x000055c810ecb951 scsi_device_purge_requests (qemu-kvm + 0> > ^^^^^^^^^^^^^^^^^^^^^^^^^^ > #7 0x000055c810ed6ab8 scsi_disk_reset (qemu-kvm + 0x48bab8) > #8 0x000055c8111dc908 resettable_phase_hold (qemu-kvm + 0x7919> > #9 0x000055c8111db7f0 device_cold_reset (qemu-kvm + 0x7907f0) > #10 0x000055c8110bb1a6 virtio_scsi_handle_ctrl (qemu-kvm + 0x67> > #11 0x000055c8110d458f virtio_queue_host_notifier_read (qemu-kv> > #12 0x000055c811404a73 aio_dispatch_handler (qemu-kvm + 0x9b9a7> > #13 0x000055c811405743 aio_poll (qemu-kvm + 0x9ba743) > #14 0x000055c81121d532 iothread_run (qemu-kvm + 0x7d2532) > #15 0x000055c81140926a qemu_thread_start (qemu-kvm + 0x9be26a) > #16 0x00007f4b6a09f802 start_thread (libc.so.6 + 0x9f802) > #17 0x00007f4b6a03f450 __clone3 (libc.so.6 + 0x3f450) > > Reported-by: Qing Wang <[email protected]> > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2155748 > Cc: Paolo Bonzini <[email protected]> > Cc: Kevin Wolf <[email protected]> > Cc: Emanuele Giuseppe Esposito <[email protected]> > Signed-off-by: Stefan Hajnoczi <[email protected]> > --- > include/sysemu/block-backend-io.h | 1 + > block/block-backend.c | 23 +++++++++++++++++++++++ > hw/scsi/scsi-bus.c | 2 +- > 3 files changed, 25 insertions(+), 1 deletion(-) > > diff --git a/include/sysemu/block-backend-io.h > b/include/sysemu/block-backend-io.h > index 7ec6d978d4..f73db1f77c 100644 > --- a/include/sysemu/block-backend-io.h > +++ b/include/sysemu/block-backend-io.h > @@ -73,6 +73,7 @@ void blk_iostatus_set_err(BlockBackend *blk, int error); > int blk_get_max_iov(BlockBackend *blk); > int blk_get_max_hw_iov(BlockBackend *blk); > > +void blk_drain_noref(BlockBackend *blk); > void blk_io_plug(BlockBackend *blk); > void blk_io_unplug(BlockBackend *blk); > AioContext *blk_get_aio_context(BlockBackend *blk); > diff --git a/block/block-backend.c b/block/block-backend.c > index ba7bf1d6bc..20914bae7b 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -1815,6 +1815,29 @@ void blk_drain(BlockBackend *blk) > } > } > > +/* > + * Same as blk_drain() but the caller must hold a reference to blk. May be > + * called from Global State or I/O API code. Device emulation can call > this > + * because the qdev drive= property holds the reference. > + */ > +void blk_drain_noref(BlockBackend *blk) > +{ > + BlockDriverState *bs = blk_bs(blk); > + IO_OR_GS_CODE(); > + > + if (bs) { > + bdrv_drained_begin(bs); > + } > + > + /* We may have -ENOMEDIUM completions in flight */ > + AIO_WAIT_WHILE(blk_get_aio_context(blk), > + qatomic_mb_read(&blk->in_flight) > 0); > + > + if (bs) { > + bdrv_drained_end(bs); > + } > +} > + > void blk_drain_all(void) > { > BlockBackend *blk = NULL; > diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c > index ceceafb2cd..110fd85106 100644 > --- a/hw/scsi/scsi-bus.c > +++ b/hw/scsi/scsi-bus.c > @@ -1663,7 +1663,7 @@ void scsi_device_purge_requests(SCSIDevice *sdev, > SCSISense sense) > req = QTAILQ_FIRST(&sdev->requests); > scsi_req_cancel_async(req, NULL); > } > - blk_drain(sdev->conf.blk); > + blk_drain_noref(sdev->conf.blk); > aio_context_release(blk_get_aio_context(sdev->conf.blk)); > scsi_device_set_ua(sdev, sense); > } > -- > 2.39.0 > >
