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Re: [PATCH 4/5] blkdebug: do not suspend in the middle of QLIST_FOREACH_

From: Paolo Bonzini
Subject: Re: [PATCH 4/5] blkdebug: do not suspend in the middle of QLIST_FOREACH_SAFE
Date: Tue, 13 Apr 2021 09:48:56 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

On 08/04/21 17:59, Emanuele Giuseppe Esposito wrote:

Perhaps insert here:

That would be unsafe in case a rule other than the current one is removed while the coroutine has yielded. Keep FOREACH_SAFE because suspend_request deletes the current rule.

After this patch, *all* matching rules are deleted before suspending the coroutine, rather than just one. This doesn't affect the existing testcases.

Use actions_count to see how many yeld to issue.

Co-developed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
  block/blkdebug.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blkdebug.c b/block/blkdebug.c
index 388b5ed615..dffd869b32 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -789,7 +789,6 @@ static void suspend_request(BlockDriverState *bs, 
BlkdebugRule *rule)
      if (!qtest_enabled()) {
          printf("blkdebug: Suspended request '%s'\n", r->tag);
-    qemu_coroutine_yield();
static void process_rule(BlockDriverState *bs, struct BlkdebugRule *rule,
@@ -834,6 +833,12 @@ static void blkdebug_debug_event(BlockDriverState *bs, 
BlkdebugEvent event)
      QLIST_FOREACH_SAFE(rule, &s->rules[event], next, next) {
          process_rule(bs, rule, actions_count);
+    while (actions_count[ACTION_SUSPEND] > 0) {
+        qemu_coroutine_yield();
+        actions_count[ACTION_SUSPEND]--;
+    }
      s->state = s->new_state;

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