a937f8e857
virtio_blk_dma_restart_cb() is tricky because the BH must deal with
virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() being called.
There are two issues with the code:
1. virtio_blk_realize() should use qdev_add_vm_change_state_handler()
instead of qemu_add_vm_change_state_handler(). This ensures the
ordering with virtio_init()'s vm change state handler that calls
virtio_blk_data_plane_start()/virtio_blk_data_plane_stop() is
well-defined. Then blk's AioContext is guaranteed to be up-to-date in
virtio_blk_dma_restart_cb() and it's no longer necessary to have a
special case for virtio_blk_data_plane_start().
2. Only blk_drain() waits for virtio_blk_dma_restart_cb()'s
blk_inc_in_flight() to be decremented. The bdrv_drain() family of
functions do not wait for BlockBackend's in_flight counter to reach
zero. virtio_blk_data_plane_stop() relies on blk_set_aio_context()'s
implicit drain, but that's a bdrv_drain() and not a blk_drain().
Note that virtio_blk_reset() already correctly relies on blk_drain().
If virtio_blk_data_plane_stop() switches to blk_drain() then we can
properly wait for pending virtio_blk_dma_restart_bh() calls.
Once these issues are taken care of the code becomes simpler. This
change is in preparation for multiple IOThreads in virtio-blk where we
need to clean up the multi-threading behavior.
I ran the reproducer from commit
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| .. | ||
| acpi | ||
| adc | ||
| arm | ||
| audio | ||
| block | ||
| char | ||
| core | ||
| cpu | ||
| cris | ||
| cxl | ||
| display | ||
| dma | ||
| firmware | ||
| gpio | ||
| hyperv | ||
| i2c | ||
| i386 | ||
| ide | ||
| input | ||
| intc | ||
| ipack | ||
| ipmi | ||
| isa | ||
| kvm | ||
| loongarch | ||
| m68k | ||
| mem | ||
| mips | ||
| misc | ||
| net | ||
| nubus | ||
| nvram | ||
| openrisc | ||
| pci | ||
| pci-bridge | ||
| pci-host | ||
| ppc | ||
| rdma | ||
| remote | ||
| riscv | ||
| rtc | ||
| rx | ||
| s390x | ||
| scsi | ||
| sd | ||
| sensor | ||
| sh4 | ||
| southbridge | ||
| sparc | ||
| ssi | ||
| timer | ||
| tricore | ||
| usb | ||
| vfio | ||
| virtio | ||
| watchdog | ||
| xen | ||
| xtensa | ||
| boards.h | ||
| clock.h | ||
| elf_ops.h | ||
| fw-path-provider.h | ||
| hotplug.h | ||
| hw.h | ||
| ide.h | ||
| irq.h | ||
| loader-fit.h | ||
| loader.h | ||
| nmi.h | ||
| or-irq.h | ||
| pcmcia.h | ||
| platform-bus.h | ||
| ptimer.h | ||
| qdev-clock.h | ||
| qdev-core.h | ||
| qdev-dma.h | ||
| qdev-properties-system.h | ||
| qdev-properties.h | ||
| register.h | ||
| registerfields.h | ||
| resettable.h | ||
| stream.h | ||
| sysbus.h | ||
| usb.h | ||
| vmstate-if.h | ||