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[Qemu-devel] [PATCH v10 01/16] block: Pause all jobs during bdrv_reopen_
From: |
Alberto Garcia |
Subject: |
[Qemu-devel] [PATCH v10 01/16] block: Pause all jobs during bdrv_reopen_multiple() |
Date: |
Thu, 6 Oct 2016 16:02:44 +0300 |
When a BlockDriverState is about to be reopened it can trigger certain
operations that need to write to disk. During this process a different
block job can be woken up. If that block job completes and also needs
to call bdrv_reopen() it can happen that it needs to do it on the same
BlockDriverState that is still in the process of being reopened.
This can have fatal consequences, like in this example:
1) Block job A starts and sleeps after a while.
2) Block job B starts and tries to reopen node1 (a qcow2 file).
3) Reopening node1 means flushing and replacing its qcow2 cache.
4) While the qcow2 cache is being flushed, job A wakes up.
5) Job A completes and reopens node1, replacing its cache.
6) Job B resumes, but the cache that was being flushed no longer
exists.
This patch pauses all block jobs during bdrv_reopen_multiple(), so
that step 4 can never happen and the operation is safe.
Note that this scenario can only happen if both bdrv_reopen() calls
are made by block jobs on the same backing chain. Otherwise there's no
chance that the same BlockDriverState appears in both reopen queues.
Signed-off-by: Alberto Garcia <address@hidden>
---
block.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/block.c b/block.c
index bb1f1ec..c80b528 100644
--- a/block.c
+++ b/block.c
@@ -2087,9 +2087,19 @@ int bdrv_reopen_multiple(BlockReopenQueue *bs_queue,
Error **errp)
int ret = -1;
BlockReopenQueueEntry *bs_entry, *next;
Error *local_err = NULL;
+ BlockJob *job = NULL;
assert(bs_queue != NULL);
+ /* Pause all block jobs */
+ while ((job = block_job_next(job))) {
+ AioContext *aio_context = blk_get_aio_context(job->blk);
+
+ aio_context_acquire(aio_context);
+ block_job_pause(job);
+ aio_context_release(aio_context);
+ }
+
bdrv_drain_all();
QSIMPLEQ_FOREACH(bs_entry, bs_queue, entry) {
@@ -2120,6 +2130,17 @@ cleanup:
g_free(bs_entry);
}
g_free(bs_queue);
+
+ /* Resume all block jobs */
+ job = NULL;
+ while ((job = block_job_next(job))) {
+ AioContext *aio_context = blk_get_aio_context(job->blk);
+
+ aio_context_acquire(aio_context);
+ block_job_resume(job);
+ aio_context_release(aio_context);
+ }
+
return ret;
}
--
2.9.3
- [Qemu-devel] [PATCH v10 06/16] block: Block all nodes involved in the block-commit operation, (continued)
- [Qemu-devel] [PATCH v10 01/16] block: Pause all jobs during bdrv_reopen_multiple(),
Alberto Garcia <=
[Qemu-devel] [PATCH v10 05/16] block: Check blockers in all nodes involved in a block-commit job, Alberto Garcia, 2016/10/06
[Qemu-devel] [PATCH v10 03/16] block: Use block_job_add_bdrv() in mirror_start_job(), Alberto Garcia, 2016/10/06