From 1a6d3bd229d429879a85a9105fb84cae049d083c Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Fri, 23 Oct 2020 17:01:10 +0200 Subject: [PATCH] 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 --- block.c | 9 +++++++++ block/io.c | 13 +++++++++++++ include/block/block.h | 6 ++++++ tests/test-bdrv-drain.c | 1 + 4 files changed, 29 insertions(+) diff --git a/block.c b/block.c index 430edf79bb..ee5b28a979 100644 --- a/block.c +++ b/block.c @@ -4458,6 +4458,15 @@ static void bdrv_close(BlockDriverState *bs) } QLIST_INIT(&bs->aio_notifiers); bdrv_drained_end(bs); + + /* + * If we're still inside some bdrv_drain_all_begin()/end() sections, end + * them now since this BDS won't exist anymore when bdrv_drain_all_end() + * gets called. + */ + if (bs->quiesce_counter) { + bdrv_drain_all_end_quiesce(bs); + } } void bdrv_close_all(void) diff --git a/block/io.c b/block/io.c index c33cecd58d..9918f2499c 100644 --- a/block/io.c +++ b/block/io.c @@ -633,6 +633,19 @@ void bdrv_drain_all_begin(void) } } +void bdrv_drain_all_end_quiesce(BlockDriverState *bs) +{ + int drained_end_counter = 0; + + g_assert(bs->quiesce_counter > 0); + g_assert(!bs->refcnt); + + while (bs->quiesce_counter) { + bdrv_do_drained_end(bs, false, NULL, true, &drained_end_counter); + } + BDRV_POLL_WHILE(bs, qatomic_read(&drained_end_counter) > 0); +} + void bdrv_drain_all_end(void) { BlockDriverState *bs = NULL; diff --git a/include/block/block.h b/include/block/block.h index c9d7c58765..4bfe3b546b 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -781,6 +781,12 @@ void bdrv_drained_end(BlockDriverState *bs); */ void bdrv_drained_end_no_poll(BlockDriverState *bs, int *drained_end_counter); +/** + * End all quiescent sections started by bdrv_drain_all_begin(). This is + * only needed when deleting a BDS before bdrv_drain_all_end() is called. + */ +void bdrv_drain_all_end_quiesce(BlockDriverState *bs); + /** * End a quiescent section started by bdrv_subtree_drained_begin(). */ diff --git a/tests/test-bdrv-drain.c b/tests/test-bdrv-drain.c index 1595bbc92e..8a29e33e00 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);