diff mbox series

[v3,2/5] blkdebug: move post-resume handling to resume_req_by_tag

Message ID 20210517145049.55268-3-eesposit@redhat.com
State New
Headers show
Series blkdebug: fix racing condition when iterating on | expand

Commit Message

Emanuele Giuseppe Esposito May 17, 2021, 2:50 p.m. UTC 
We want to move qemu_coroutine_yield() after the loop on rules,
because QLIST_FOREACH_SAFE is wrong if the rule list is modified
while the coroutine has yielded.  Therefore move the suspended
request to the heap and clean it up from the remove side.
All that is left is for blkdebug_debug_event to handle the
yielding.

Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/blkdebug.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

Comments

Vladimir Sementsov-Ogievskiy May 31, 2021, 7:50 p.m. UTC | #1 
17.05.2021 17:50, Emanuele Giuseppe Esposito wrote:
> We want to move qemu_coroutine_yield() after the loop on rules,
> because QLIST_FOREACH_SAFE is wrong if the rule list is modified
> while the coroutine has yielded.  Therefore move the suspended
> request to the heap and clean it up from the remove side.
> All that is left is for blkdebug_debug_event to handle the
> yielding.
> 
> Co-developed-by: Paolo Bonzini<pbonzini@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito<eesposit@redhat.com>


Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
diff mbox series

Patch

diff --git a/block/blkdebug.c b/block/blkdebug.c
index 8f19d991fa..e37f999254 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -775,25 +775,20 @@  static void blkdebug_close(BlockDriverState *bs)
 static void suspend_request(BlockDriverState *bs, BlkdebugRule *rule)
 {
     BDRVBlkdebugState *s = bs->opaque;
-    BlkdebugSuspendedReq r;
+    BlkdebugSuspendedReq *r;
 
-    r = (BlkdebugSuspendedReq) {
-        .co         = qemu_coroutine_self(),
-        .tag        = g_strdup(rule->options.suspend.tag),
-    };
+    r = g_new(BlkdebugSuspendedReq, 1);
+
+    r->co         = qemu_coroutine_self();
+    r->tag        = g_strdup(rule->options.suspend.tag);
 
     remove_rule(rule);
-    QLIST_INSERT_HEAD(&s->suspended_reqs, &r, next);
+    QLIST_INSERT_HEAD(&s->suspended_reqs, r, next);
 
     if (!qtest_enabled()) {
-        printf("blkdebug: Suspended request '%s'\n", r.tag);
+        printf("blkdebug: Suspended request '%s'\n", r->tag);
     }
     qemu_coroutine_yield();
-    if (!qtest_enabled()) {
-        printf("blkdebug: Resuming request '%s'\n", r.tag);
-    }
-
-    g_free(r.tag);
 }
 
 static bool process_rule(BlockDriverState *bs, struct BlkdebugRule *rule,
@@ -875,8 +870,18 @@  static int resume_req_by_tag(BDRVBlkdebugState *s, const char *tag, bool all)
 retry:
     QLIST_FOREACH(r, &s->suspended_reqs, next) {
         if (!strcmp(r->tag, tag)) {
+            Coroutine *co = r->co;
+
+            if (!qtest_enabled()) {
+                printf("blkdebug: Resuming request '%s'\n", r->tag);
+            }
+
             QLIST_REMOVE(r, next);
-            qemu_coroutine_enter(r->co);
+            g_free(r->tag);
+            g_free(r);
+
+            qemu_coroutine_enter(co);
+
             if (all) {
                 goto retry;
             }