[dm-devel] [PATCH v2 1/2] libmultipath: fix race in stop_io_err_stat_thread

[Hannes Reinecke]

On 03/06/2018 10:18 PM, Martin Wilck wrote:
> It's wrong, and unnecessary, to call pthread_kill after
> pthread_cancel. I have observed cases where the io_err checker
> thread hung in libpthread after receiving the USR2 signal, in particular
> when multipathd is run under strace. (If multipathd is killed with
> SIGINT under strace, and the io_error thread is running, it happens
> almost every time). If this happens, the io_err thread
> tries to obtain a mutex in the urcu code (presumably rcu_unregister_thread())
> and the main thread hangs in pthread_join().
> 
> With the change from this patch, the thread is shut down cleanly. I haven't
> observed the hang under strace with the patch.
> 
> Signed-off-by: Martin Wilck <mwilck at suse.com>
> ---
>  libmultipath/io_err_stat.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/libmultipath/io_err_stat.c b/libmultipath/io_err_stat.c
> index 00bac9e0e755..536ba87968fd 100644
> --- a/libmultipath/io_err_stat.c
> +++ b/libmultipath/io_err_stat.c
> @@ -749,7 +749,6 @@ destroy_ctx:
>  void stop_io_err_stat_thread(void)
>  {
>  	pthread_cancel(io_err_stat_thr);
> -	pthread_kill(io_err_stat_thr, SIGUSR2);
>  	pthread_join(io_err_stat_thr, NULL);
>  	free_io_err_pathvec(paths);
>  	io_destroy(ioctx);
> 
Good point.

Reviewed-by: Hannes Reinecke <hare at suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare at suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)