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AIO_WAIT_WHILE questions
From: |
Dietmar Maurer |
Subject: |
AIO_WAIT_WHILE questions |
Date: |
Fri, 27 Mar 2020 17:36:23 +0100 (CET) |
Hi all,
I have a question about AIO_WAIT_WHILE. The docs inside the code say:
* The caller's thread must be the IOThread that owns @ctx or the main loop
* thread (with @ctx acquired exactly once).
I wonder if that "with @ctx acquired exactly once" is always required?
I have done a quick test (see code below) and this reveals that the condition
is not
always met.
Or is my test wrong (or the docs)?
---debug helper---
diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index afeeb18f95..cf78dca9f9 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -82,6 +82,8 @@ extern AioWait global_aio_wait;
atomic_inc(&wait_->num_waiters); \
if (ctx_ && in_aio_context_home_thread(ctx_)) { \
while ((cond)) { \
+ printf("AIO_WAIT_WHILE %p %d\n", ctx, ctx_->lock_count); \
+ assert(ctx_->lock_count == 1); \
aio_poll(ctx_, true); \
waited_ = true; \
} \
diff --git a/include/block/aio.h b/include/block/aio.h
index cb1989105a..51ef20e2f0 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -125,6 +125,7 @@ struct AioContext {
/* Used by AioContext users to protect from multi-threaded access. */
QemuRecMutex lock;
+ int lock_count;
/* The list of registered AIO handlers. Protected by ctx->list_lock. */
AioHandlerList aio_handlers;
diff --git a/util/async.c b/util/async.c
index b94518b948..9804c6c64f 100644
--- a/util/async.c
+++ b/util/async.c
@@ -594,9 +594,11 @@ void aio_context_unref(AioContext *ctx)
void aio_context_acquire(AioContext *ctx)
{
qemu_rec_mutex_lock(&ctx->lock);
+ ctx->lock_count++;
}
void aio_context_release(AioContext *ctx)
{
+ ctx->lock_count--;
qemu_rec_mutex_unlock(&ctx->lock);
}
- AIO_WAIT_WHILE questions,
Dietmar Maurer <=