[dm-devel] [PATCH 2/2] multipathd: Avoid that a deadlock is triggered sporadically during shutdown

[Xose Vazquez Perez]

On 10/14/2016 05:35 PM, Bart Van Assche wrote:

> pthread_cond_wait() is a thread cancellation point. If a thread that
> is waiting in pthread_cond_wait() is canceled it is possible that the
> mutex is re-acquired before the first cancellation cleanup handler
> is called. In this case the cleanup handler is uevq_stop() and that
> function locks uevq_lock. Avoid that calling uevq_stop() results in
> a deadlock due to an attempt to lock a non-recursive mutex recursively.
> 
> Signed-off-by: Bart Van Assche <bart.vanassche at sandisk.com>
> ---
>  libmultipath/uevent.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libmultipath/uevent.c b/libmultipath/uevent.c
> index 6247898..85fd2fb 100644
> --- a/libmultipath/uevent.c
> +++ b/libmultipath/uevent.c
> @@ -52,7 +52,7 @@ typedef int (uev_trigger)(struct uevent *, void * trigger_data);
>  
>  pthread_t uevq_thr;
>  LIST_HEAD(uevq);
> -pthread_mutex_t uevq_lock = PTHREAD_MUTEX_INITIALIZER;
> +pthread_mutex_t uevq_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
>  pthread_mutex_t *uevq_lockp = &uevq_lock;
>  pthread_cond_t uev_cond = PTHREAD_COND_INITIALIZER;
>  pthread_cond_t *uev_condp = &uev_cond;
> 

PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP is not defined in POSIX.

This is going to be problematic in musl-libc based distributions:
http://wiki.musl-libc.org/wiki/Projects_using_musl#Distributions


~/musl-gcc -O2 -g -pipe -Wall -Wextra -Wformat=2 -Wno-sign-compare -Wno-unused-parameter -Wno-clobbered -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector --param=ssp-buffer-size=4 -fPIC -DLIB_STRING=\"lib64\"
-DRUN_DIR=\"run\" -I../libmpathcmd -DUSE_SYSTEMD=229 -DLIBDM_API_FLUSH -D_GNU_SOURCE -DLIBDM_API_COOKIE -DLIBUDEV_API_RECVBUF -DLIBDM_API_DEFERRED -c -o uevent.o uevent.c
uevent.c:55:29: error: ‘PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP’ undeclared here (not in a function)
 pthread_mutex_t uevq_lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../Makefile.inc:74: recipe for target 'uevent.o' failed
make[1]: [uevent.o] Error 1 (ignored)