From: Evgeny Yakovlev <eyakov...@virtuozzo.com>
The following commit
commit 3ff2f67a7c24183fcbcfe1332e5223ac6f96438c
Author: Evgeny Yakovlev <eyakov...@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 <eyakov...@virtuozzo.com>
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Stefan Hajnoczi <stefa...@redhat.com>
CC: Fam Zheng <f...@redhat.com>
CC: Kevin Wolf <kw...@redhat.com>
CC: Max Reitz <mre...@redhat.com>
---
block/io.c | 5 +++--
include/block/block_int.h | 2 +-
2 files changed, 4 insertions(+), 3 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);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 47665be..1e939de 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -443,8 +443,8 @@ struct BlockDriverState {
note this is a reference count */
CoQueue flush_queue; /* Serializing flush queue */
+ BdrvTrackedRequest *active_flush_req; /* Flush request in flight */
unsigned int write_gen; /* Current data generation */
- unsigned int flush_started_gen; /* Generation for which flush has started
*/
unsigned int flushed_gen; /* Flushed write generation */
BlockDriver *drv; /* NULL means no media */
--
2.7.4
