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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: cf3129323f
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200407121259.21350-4-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
master
Kevin Wolf 2020-04-07 14:12:59 +02:00
parent fbb92b6798
commit 7f16476fab
1 changed files with 5 additions and 12 deletions
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17
block/block-backend.c
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@ -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);