Commit 9b536adc authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

block: acquire AioContext in bdrv_drain_all() 



Modify bdrv_drain_all() to take into account that BlockDriverState
instances may be running in different AioContexts.

This patch changes the implementation of bdrv_drain_all() while
preserving the semantics.  Previously kicking throttled requests and
checking for pending requests were done across all BlockDriverState
instances in sequence.  Now we process each BlockDriverState in turn,
making sure to acquire and release its AioContext.

This prevents race conditions between the thread executing
bdrv_drain_all() and the thread running the AioContext.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent ed78cda3

block.c

+11 −14
Original line number Diff line number Diff line
@@ -1885,17 +1885,6 @@ static bool bdrv_requests_pending(BlockDriverState *bs) 
    return false;

}



static bool bdrv_requests_pending_all(void)

{

    BlockDriverState *bs;

    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {

        if (bdrv_requests_pending(bs)) {

            return true;

        }

    }

    return false;

}



/*

 * Wait for pending requests to complete across all BlockDriverStates

 *
@@ -1915,12 +1904,20 @@ void bdrv_drain_all(void) 
    BlockDriverState *bs;



    while (busy) {

        busy = false;



        QTAILQ_FOREACH(bs, &bdrv_states, device_list) {

            AioContext *aio_context = bdrv_get_aio_context(bs);

            bool bs_busy;



            aio_context_acquire(aio_context);

            bdrv_start_throttled_reqs(bs);

        }

            bs_busy = bdrv_requests_pending(bs);

            bs_busy |= aio_poll(aio_context, bs_busy);

            aio_context_release(aio_context);



        busy = bdrv_requests_pending_all();

        busy |= aio_poll(qemu_get_aio_context(), busy);

            busy |= bs_busy;

        }

    }

}