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| author | Evgeny Yakovlev <eyakovlev@virtuozzo.com> | 2016-08-17 21:06:53 +0300 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2016-08-18 14:36:49 +0100 |
| commit | ce83ee57f6fa69280a0330f1b49ef75b0ef0742a (patch) | |
| tree | f88d10fc7bee32449e22c7b092d316c337535c53 | |
| parent | 5844365fe8e5e4598222d276d2af54fd45c7e3d3 (diff) | |
| download | qemu-ce83ee57f6fa69280a0330f1b49ef75b0ef0742a.tar.gz | |
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>
| -rw-r--r-- | block/io.c | 5 | ||||
| -rw-r--r-- | include/block/block_int.h | 2 |
2 files changed, 4 insertions, 3 deletions
diff --git a/block/io.c b/block/io.c index d5493ba349..9c04086286 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 47665be81e..1e939de4fe 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 */ |