Commit 7f16476f authored by Kevin Wolf's avatar Kevin Wolf
Browse files

block: Fix blk->in_flight during blk_wait_while_drained() 



Waiting in blk_wait_while_drained() while blk->in_flight is increased
for the current request is wrong because it will cause the drain
operation to deadlock.

This patch makes sure that blk_wait_while_drained() is called with
blk->in_flight increased exactly once for the current request, and that
it temporarily decreases the counter while it waits.

Fixes: cf312932
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Reviewed-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: default avatarMax Reitz <mreitz@redhat.com>
Message-Id: <20200407121259.21350-4-kwolf@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent fbb92b67

block/block-backend.c

+5 −12
Original line number Diff line number Diff line
@@ -1140,10 +1140,15 @@ static int blk_check_byte_request(BlockBackend *blk, int64_t offset, 
    return 0;

}



/* To be called between exactly one pair of blk_inc/dec_in_flight() */

static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)

{

    assert(blk->in_flight > 0);



    if (blk->quiesce_counter && !blk->disable_request_queuing) {

        blk_dec_in_flight(blk);

        qemu_co_queue_wait(&blk->queued_requests, NULL);

        blk_inc_in_flight(blk);

    }

}
@@ -1418,12 +1423,6 @@ static void blk_aio_read_entry(void *opaque) 
    BlkRwCo *rwco = &acb->rwco;

    QEMUIOVector *qiov = rwco->iobuf;



    if (rwco->blk->quiesce_counter) {

        blk_dec_in_flight(rwco->blk);

        blk_wait_while_drained(rwco->blk);

        blk_inc_in_flight(rwco->blk);

    }



    assert(qiov->size == acb->bytes);

    rwco->ret = blk_do_preadv(rwco->blk, rwco->offset, acb->bytes,

                              qiov, rwco->flags);
@@ -1436,12 +1435,6 @@ static void blk_aio_write_entry(void *opaque) 
    BlkRwCo *rwco = &acb->rwco;

    QEMUIOVector *qiov = rwco->iobuf;



    if (rwco->blk->quiesce_counter) {

        blk_dec_in_flight(rwco->blk);

        blk_wait_while_drained(rwco->blk);

        blk_inc_in_flight(rwco->blk);

    }



    assert(!qiov || qiov->size == acb->bytes);

    rwco->ret = blk_do_pwritev_part(rwco->blk, rwco->offset, acb->bytes,

                                    qiov, 0, rwco->flags);