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graph-lock: Unlock the AioContext while polling

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If the caller keeps the AioContext lock for a block node in an iothread,
polling in bdrv_graph_wrlock() deadlocks if the condition isn't
fulfilled immediately.

Now that all callers make sure to actually have the AioContext locked
when they call bdrv_replace_child_noperm() like they should, we can
change bdrv_graph_wrlock() to take a BlockDriverState whose AioContext
lock the caller holds (NULL if it doesn't) and unlock it temporarily
while polling.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-11-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2023-06-05 10:57:10 +02:00
parent 22dd940544
commit 31b2ddfea3
3 changed files with 28 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

6
include/block/graph-lock.h
View file

@ -111,10 +111,12 @@ void unregister_aiocontext(AioContext *ctx);
* The wrlock can only be taken from the main loop, with BQL held, as only the
* main loop is allowed to modify the graph.
*
* If @bs is non-NULL, its AioContext is temporarily released.
*
* This function polls. Callers must not hold the lock of any AioContext other
* than the current one.
* than the current one and the one of @bs.
*/
void bdrv_graph_wrlock(void) TSA_ACQUIRE(graph_lock) TSA_NO_TSA;
void bdrv_graph_wrlock(BlockDriverState *bs) TSA_ACQUIRE(graph_lock) TSA_NO_TSA;
/*
* bdrv_graph_wrunlock: