From 1a6d3bd229d429879a85a9105fb84cae049d083c Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Fri, 23 Oct 2020 17:01:10 +0200 Subject: 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 Message-Id: <160346526998.272601.9045392804399803158.stgit@bahia.lan> Signed-off-by: Kevin Wolf --- tests/test-bdrv-drain.c | 1 + 1 file changed, 1 insertion(+) (limited to 'tests') diff --git a/tests/test-bdrv-drain.c b/tests/test-bdrv-drain.c index 1595bbc..8a29e33 100644 --- a/tests/test-bdrv-drain.c +++ b/tests/test-bdrv-drain.c @@ -594,6 +594,7 @@ static void test_graph_change_drain_all(void) g_assert_cmpint(bs_b->quiesce_counter, ==, 0); g_assert_cmpint(b_s->drain_count, ==, 0); + g_assert_cmpint(qemu_get_aio_context()->external_disable_cnt, ==, 0); bdrv_unref(bs_b); blk_unref(blk_b); -- cgit v1.1