Re: [Qemu-devel] [PATCH] posix-aio: don't set aiocb->ret/active outside critical section

[Kevin Wolf]

Am 15.05.2012 13:27, schrieb Jim Meyering:
> 
> Move code that sets aiocb->ret and aiocb->active into critical section.
> All other accesses are lock-guarded.  Spotted by coverity.
> 
> Signed-off-by: Jim Meyering <address@hidden>
> ---
> I've included enough context to show one of the
> guarded uses in the following function.
> 
>  posix-aio-compat.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/posix-aio-compat.c b/posix-aio-compat.c
> index 68361f5..45511d4 100644
> --- a/posix-aio-compat.c
> +++ b/posix-aio-compat.c
> @@ -421,37 +421,37 @@ static void spawn_thread(void)
>  {
>      cur_threads++;
>      new_threads++;
>      /* If there are threads being created, they will spawn new workers, so
>       * we don't spend time creating many threads in a loop holding a mutex or
>       * starving the current vcpu.
>       *
>       * If there are no idle threads, ask the main thread to create one, so we
>       * inherit the correct affinity instead of the vcpu affinity.
>       */
>      if (!pending_threads) {
>          qemu_bh_schedule(new_thread_bh);
>      }
>  }
> 
>  static void qemu_paio_submit(struct qemu_paiocb *aiocb)
>  {
> +    mutex_lock(&lock);
>      aiocb->ret = -EINPROGRESS;
>      aiocb->active = 0;
> -    mutex_lock(&lock);
>      if (idle_threads == 0 && cur_threads < max_threads)
>          spawn_thread();
>      QTAILQ_INSERT_TAIL(&request_list, aiocb, node);
>      mutex_unlock(&lock);
>      cond_signal(&cond);
>  }

This is just silencing coverity, not really fixing a bug, right? aiocb
is inserted into request_lists only afterwards, and before it is in the
list, other threads can't find it.

I'm just wondering why coverity doesn't complain about the callers of
qemu_paio_submit(), they access aiocb as well...

Kevin