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block: make BlockBackend->disable_request_queuing atomic 

This field is accessed by multiple threads without a lock. Use explicit
qatomic_read()/qatomic_set() calls. There is no need for acquire/release
because blk_set_disable_request_queuing() doesn't provide any
guarantees (it helps that it's used at BlockBackend creation time and
not when there is I/O in flight).

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230307210427.269214-3-stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-03-07 16:04:26 -05:00 committed by Kevin Wolf
parent c4d5bf99b7
commit ef80ec5067
1 changed files with 4 additions and 3 deletions
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7
block/block-backend.c
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@ -82,7 +82,7 @@ struct BlockBackend {
int quiesce_counter; /* atomic: written under BQL, read by other threads */
CoQueue queued_requests;
bool disable_request_queuing;
bool disable_request_queuing; /* atomic */
VMChangeStateEntry *vmsh;
bool force_allow_inactivate;
@ -1232,7 +1232,7 @@ void blk_set_allow_aio_context_change(BlockBackend *blk, bool allow)
void blk_set_disable_request_queuing(BlockBackend *blk, bool disable)
{
IO_CODE();
blk->disable_request_queuing = disable;
qatomic_set(&blk->disable_request_queuing, disable);
}
static int coroutine_fn GRAPH_RDLOCK
@ -1271,7 +1271,8 @@ static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
{
assert(blk->in_flight > 0);
if (qatomic_read(&blk->quiesce_counter) && !blk->disable_request_queuing) {
if (qatomic_read(&blk->quiesce_counter) &&
!qatomic_read(&blk->disable_request_queuing)) {
blk_dec_in_flight(blk);
qemu_co_queue_wait(&blk->queued_requests, NULL);
blk_inc_in_flight(blk);