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author | Greg Kurz <groug@kaod.org> | 2020-10-23 17:01:10 +0200 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2020-10-27 15:26:20 +0100 |
commit | 1a6d3bd229d429879a85a9105fb84cae049d083c (patch) | |
tree | ffb7af4fb4561e489dfd196a0312a9b8d782d960 /docs | |
parent | 46cd1e8a4752379b1b9d24d43d7be7d5aba03e76 (diff) | |
download | qemu-1a6d3bd229d429879a85a9105fb84cae049d083c.zip qemu-1a6d3bd229d429879a85a9105fb84cae049d083c.tar.gz qemu-1a6d3bd229d429879a85a9105fb84cae049d083c.tar.bz2 |
block: End quiescent sections when a BDS is deleted
If a BDS gets deleted during blk_drain_all(), it might miss a
call to bdrv_do_drained_end(). This means missing a call to
aio_enable_external() and the AIO context remains disabled for
ever. This can cause a device to become irresponsive and to
disrupt the guest execution, ie. hang, loop forever or worse.
This scenario is quite easy to encounter with virtio-scsi
on POWER when punching multiple blockdev-create QMP commands
while the guest is booting and it is still running the SLOF
firmware. This happens because SLOF disables/re-enables PCI
devices multiple times via IO/MEM/MASTER bits of PCI_COMMAND
register after the initial probe/feature negotiation, as it
tends to work with a single device at a time at various stages
like probing and running block/network bootloaders without
doing a full reset in-between. This naturally generates many
dataplane stops and starts, and thus many drain sections that
can race with blockdev_create_run(). In the end, SLOF bails
out.
It is somehow reproducible on x86 but it requires to generate
articial dataplane start/stop activity with stop/cont QMP
commands. In this case, seabios ends up looping for ever,
waiting for the virtio-scsi device to send a response to
a command it never received.
Add a helper that pairs all previously called bdrv_do_drained_begin()
with a bdrv_do_drained_end() and call it from bdrv_close().
While at it, update the "/bdrv-drain/graph-change/drain_all"
test in test-bdrv-drain so that it can catch the issue.
BugId: https://bugzilla.redhat.com/show_bug.cgi?id=1874441
Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <160346526998.272601.9045392804399803158.stgit@bahia.lan>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'docs')
0 files changed, 0 insertions, 0 deletions