commit ef80ec5067d7ca5b46e5b88be1be33cddfd33551
author Stefan Hajnoczi <stefanha@redhat.com> Tue Mar 07 16:04:26 2023 -0500
committer Kevin Wolf <kwolf@redhat.com> Tue Apr 25 13:15:21 2023 +0200
tree e34b78dcb1dbdad2cdf7618ab3ac03670d838128
parent c4d5bf99b7fccf8849316b9f5100525b1beb8237

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>

block/block-backend.c

diff --git a/block/block-backend.c b/block/block-backend.c
index 2ae768f..8552b6d 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -82,7 +82,7 @@
 
     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_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 @@
 {
     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);