Hide the clearing of job->busy in a single function, and set it
in block_job_enter.  This lets block_job_do_yield verify that
qemu_coroutine_enter is not used while job->busy = false.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 blockjob.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/blockjob.c b/blockjob.c
index db9e4fc89a..4d22b7d2fb 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -729,6 +729,15 @@ static bool block_job_should_pause(BlockJob *job)
     return job->pause_count > 0;
 }
 
+static void block_job_do_yield(BlockJob *job)
+{
+    job->busy = false;
+    qemu_coroutine_yield();
+
+    /* Set by block_job_enter before re-entering the coroutine.  */
+    assert(job->busy);
+}
+
 void coroutine_fn block_job_pause_point(BlockJob *job)
 {
     assert(job && block_job_started(job));
@@ -746,9 +755,7 @@ void coroutine_fn block_job_pause_point(BlockJob *job)
 
     if (block_job_should_pause(job) && !block_job_is_cancelled(job)) {
         job->paused = true;
-        job->busy = false;
-        qemu_coroutine_yield(); /* wait for block_job_resume() */
-        job->busy = true;
+        block_job_do_yield(job);
         job->paused = false;
     }
 
@@ -778,9 +785,12 @@ void block_job_enter(BlockJob *job)
         return;
     }
 
-    if (!job->busy) {
-        bdrv_coroutine_enter(blk_bs(job->blk), job->co);
+    if (job->busy) {
+        return;
     }
+
+    job->busy = true;
+    aio_co_wake(job->co);
 }
 
 bool block_job_is_cancelled(BlockJob *job)
@@ -819,11 +829,9 @@ void block_job_yield(BlockJob *job)
         return;
     }
 
-    job->busy = false;
     if (!block_job_should_pause(job)) {
-        qemu_coroutine_yield();
+        block_job_do_yield(job);
     }
-    job->busy = true;
 
     block_job_pause_point(job);
 }
-- 
2.14.3

On Wed, Nov 29, 2017 at 11:25:12AM +0100, Paolo Bonzini wrote:
> Hide the clearing of job->busy in a single function, and set it
> in block_job_enter.  This lets block_job_do_yield verify that
> qemu_coroutine_enter is not used while job->busy = false.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Jeff Cody <jcody@redhat.com>

> ---
>  blockjob.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/blockjob.c b/blockjob.c
> index db9e4fc89a..4d22b7d2fb 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -729,6 +729,15 @@ static bool block_job_should_pause(BlockJob *job)
>      return job->pause_count > 0;
>  }
>  
> +static void block_job_do_yield(BlockJob *job)
> +{
> +    job->busy = false;
> +    qemu_coroutine_yield();
> +
> +    /* Set by block_job_enter before re-entering the coroutine.  */
> +    assert(job->busy);
> +}
> +
>  void coroutine_fn block_job_pause_point(BlockJob *job)
>  {
>      assert(job && block_job_started(job));
> @@ -746,9 +755,7 @@ void coroutine_fn block_job_pause_point(BlockJob *job)
>  
>      if (block_job_should_pause(job) && !block_job_is_cancelled(job)) {
>          job->paused = true;
> -        job->busy = false;
> -        qemu_coroutine_yield(); /* wait for block_job_resume() */
> -        job->busy = true;
> +        block_job_do_yield(job);
>          job->paused = false;
>      }
>  
> @@ -778,9 +785,12 @@ void block_job_enter(BlockJob *job)
>          return;
>      }
>  
> -    if (!job->busy) {
> -        bdrv_coroutine_enter(blk_bs(job->blk), job->co);
> +    if (job->busy) {
> +        return;
>      }
> +
> +    job->busy = true;
> +    aio_co_wake(job->co);
>  }
>  
>  bool block_job_is_cancelled(BlockJob *job)
> @@ -819,11 +829,9 @@ void block_job_yield(BlockJob *job)
>          return;
>      }
>  
> -    job->busy = false;
>      if (!block_job_should_pause(job)) {
> -        qemu_coroutine_yield();
> +        block_job_do_yield(job);
>      }
> -    job->busy = true;
>  
>      block_job_pause_point(job);
>  }
> -- 
> 2.14.3
> 
> 

On Wed, Nov 29, 2017 at 11:25:12AM +0100, Paolo Bonzini wrote:
> Hide the clearing of job->busy in a single function, and set it
> in block_job_enter.  This lets block_job_do_yield verify that
> qemu_coroutine_enter is not used while job->busy = false.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  blockjob.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>