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authorEvgeny Yakovlev <eyakovlev@virtuozzo.com>2016-08-17 21:06:53 +0300
committerStefan Hajnoczi <stefanha@redhat.com>2016-08-18 14:36:49 +0100
commitce83ee57f6fa69280a0330f1b49ef75b0ef0742a (patch)
treef88d10fc7bee32449e22c7b092d316c337535c53 /block
parent5844365fe8e5e4598222d276d2af54fd45c7e3d3 (diff)
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block: fix deadlock in bdrv_co_flush
The following commit commit 3ff2f67a7c24183fcbcfe1332e5223ac6f96438c Author: Evgeny Yakovlev <eyakovlev@virtuozzo.com> Date: Mon Jul 18 22:39:52 2016 +0300 block: ignore flush requests when storage is clean has introduced a regression. There is a problem that it is still possible for 2 requests to execute in non sequential fashion and sometimes this results in a deadlock when bdrv_drain_one/all are called for BDS with such stalled requests. 1. Current flushed_gen and flush_started_gen is 1. 2. Request 1 enters bdrv_co_flush to with write_gen 1 (i.e. the same as flushed_gen). It gets past flushed_gen != flush_started_gen and sets flush_started_gen to 1 (again, the same it was before). 3. Request 1 yields somewhere before exiting bdrv_co_flush 4. Request 2 enters bdrv_co_flush with write_gen 2. It gets past flushed_gen != flush_started_gen and sets flush_started_gen to 2. 5. Request 2 runs to completion and sets flushed_gen to 2 6. Request 1 is resumed, runs to completion and sets flushed_gen to 1. However flush_started_gen is now 2. From here on out flushed_gen is always != to flush_started_gen and all further requests will wait on flush_queue. This change replaces flush_started_gen with an explicitly tracked active flush request. Signed-off-by: Evgeny Yakovlev <eyakovlev@virtuozzo.com> Signed-off-by: Denis V. Lunev <den@openvz.org> Message-id: 1471457214-3994-2-git-send-email-den@openvz.org CC: Stefan Hajnoczi <stefanha@redhat.com> CC: Fam Zheng <famz@redhat.com> CC: Kevin Wolf <kwolf@redhat.com> CC: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'block')
-rw-r--r--block/io.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/block/io.c b/block/io.c
index d5493ba..9c04086 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2283,11 +2283,11 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
int current_gen = bs->write_gen;
/* Wait until any previous flushes are completed */
- while (bs->flush_started_gen != bs->flushed_gen) {
+ while (bs->active_flush_req != NULL) {
qemu_co_queue_wait(&bs->flush_queue);
}
- bs->flush_started_gen = current_gen;
+ bs->active_flush_req = &req;
/* Write back all layers by calling one driver function */
if (bs->drv->bdrv_co_flush) {
@@ -2357,6 +2357,7 @@ flush_parent:
out:
/* Notify any pending flushes that we have completed */
bs->flushed_gen = current_gen;
+ bs->active_flush_req = NULL;
qemu_co_queue_restart_all(&bs->flush_queue);
tracked_request_end(&req);