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From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <philmd@redhat.com>
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Date: Thu, 29 Nov 2018 15:32:11 +0100
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Subject: Re: [Qemu-devel] [PATCH RFC 2/5] qemu_thread_join: fix segmentation
 fault
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To: Fei Li <fli@suse.com>, qemu-devel@nongnu.org

Hi Fei,

On 28/11/18 11:33, Fei Li wrote:
> To avoid the segmentation fault in qemu_thread_join(), just directly
> return when the QemuThread *thread failed to be created in either
> qemu-thread-posix.c or qemu-thread-win32.c.
> 
> Signed-off-by: Fei Li <fli@suse.com>
> Reviewed-by: Fam Zheng <famz@redhat.com>
> ---
>  util/qemu-thread-posix.c | 3 +++
>  util/qemu-thread-win32.c | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> index 865e476df5..b9ab5a4711 100644
> --- a/util/qemu-thread-posix.c
> +++ b/util/qemu-thread-posix.c
> @@ -558,6 +558,9 @@ void *qemu_thread_join(QemuThread *thread)
>      int err;
>      void *ret;
>  
> +    if (!thread->thread) {
> +        return NULL;
> +    }
>      err = pthread_join(thread->thread, &ret);
>      if (err) {
>          error_exit(err, __func__);
> diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
> index 4a363ca675..1a27e1cf6f 100644
> --- a/util/qemu-thread-win32.c
> +++ b/util/qemu-thread-win32.c
> @@ -366,7 +366,7 @@ void *qemu_thread_join(QemuThread *thread)
>      HANDLE handle;
>  
>      data = thread->data;
> -    if (data->mode == QEMU_THREAD_DETACHED) {
> +    if (data == NULL || data->mode == QEMU_THREAD_DETACHED) {

Isn't it a way to hide a problem from the caller?

qemu_thread_create() always initializes thread->data.

If the thread doesn't exist you shouldn't try to join() it.

If you try to fix a bug, I'd use here:

       assert(thread->data);

Regards,

Phil.

>          return NULL;
>      }
>  
>