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From: Benjamin Marzinski <bmarzins@redhat.com>
To: mwilck@suse.com
Cc: lixiaokeng@huawei.com, dm-devel@redhat.com
Subject: Re: [dm-devel] [PATCH v2 18/29] libmultipath: fix log_thread startup and teardown
Date: Mon, 19 Oct 2020 15:00:12 -0500
Message-ID: <20201019200012.GE3384@octiron.msp.redhat.com> (raw)
In-Reply-To: <20201016104501.8700-19-mwilck@suse.com>

On Fri, Oct 16, 2020 at 12:44:50PM +0200, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> This fixes several issues with the log_thread. First, the running
> flag logq_running should be set by the thread itself, not by
> log_thread_start()/_stop(). Second, the thread was both cancelled and
> terminated via a flag (again, logq_running). It's sufficient,
> and better, to just cancel it and use logq_running as indication for
> successful termination. Third, the locking wasn't cancel-safe in some
> places. Forth, log_thread_start() and log_thread_stop() didn't wait for
> startup/teardown properly. Fifth, using (pthread_t)0 is wrong (pthread_t is
> opaque; there's no guarantee that 0 is not a valid pthread_t value). Sixth,
> pthread_cancel() was called under logq_lock, which doesn't make sense to
> me at all.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  libmultipath/log_pthread.c | 72 ++++++++++++++++++++++++++------------
>  1 file changed, 49 insertions(+), 23 deletions(-)
> 
> diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c
> index 0c327ff..3c73941 100644
> --- a/libmultipath/log_pthread.c
> +++ b/libmultipath/log_pthread.c
> @@ -13,6 +13,7 @@
>  #include "log_pthread.h"
>  #include "log.h"
>  #include "lock.h"
> +#include "util.h"
>  
>  static pthread_t log_thr;
>  
> @@ -56,44 +57,70 @@ static void flush_logqueue (void)
>  	} while (empty == 0);
>  }
>  
> +static void cleanup_log_thread(__attribute((unused)) void *arg)
> +{
> +	logdbg(stderr, "log thread exiting");
> +	pthread_mutex_lock(&logev_lock);
> +	logq_running = 0;
> +	pthread_mutex_unlock(&logev_lock);
> +}
> +
>  static void * log_thread (__attribute__((unused)) void * et)
>  {
>  	int running;
>  
>  	pthread_mutex_lock(&logev_lock);
> -	logq_running = 1;
> +	running = logq_running;
> +	if (!running)
> +		logq_running = 1;
> +	pthread_cond_signal(&logev_cond);
>  	pthread_mutex_unlock(&logev_lock);
> +	if (running)
> +		/* already started */
> +		return NULL;
> +	pthread_cleanup_push(cleanup_log_thread, NULL);
>  
>  	mlockall(MCL_CURRENT | MCL_FUTURE);
>  	logdbg(stderr,"enter log_thread\n");
>  
>  	while (1) {
>  		pthread_mutex_lock(&logev_lock);
> -		if (logq_running && !log_messages_pending)
> +		pthread_cleanup_push(cleanup_mutex, &logev_lock);
> +		while (!log_messages_pending)
> +			/* this is a cancellation point */
>  			pthread_cond_wait(&logev_cond, &logev_lock);
>  		log_messages_pending = 0;
> -		running = logq_running;
> -		pthread_mutex_unlock(&logev_lock);
> -		if (!running)
> -			break;
> +		pthread_cleanup_pop(1);
> +
>  		flush_logqueue();
>  	}
> +	pthread_cleanup_pop(1);
>  	return NULL;
>  }
>  
>  void log_thread_start (pthread_attr_t *attr)
>  {
> -	logdbg(stderr,"enter log_thread_start\n");
> +	bool err = false;
>  
> -	pthread_mutex_init(&logq_lock, NULL);
> -	pthread_mutex_init(&logev_lock, NULL);
> -	pthread_cond_init(&logev_cond, NULL);

If you remove these initializers, then these variables are
uninitialized. I realize that patch 29 makes them statically
initialized, so I'm not sure how big of an issue it is.  I guess it
depends on how much we care about the possiblity of things not working
right when bisecting an issue.

-Ben

> +	logdbg(stderr,"enter log_thread_start\n");
>  
>  	if (log_init("multipathd", 0)) {
>  		fprintf(stderr,"can't initialize log buffer\n");
>  		exit(1);
>  	}
> +
> +	pthread_mutex_lock(&logev_lock);
> +	pthread_cleanup_push(cleanup_mutex, &logev_lock);
>  	if (pthread_create(&log_thr, attr, log_thread, NULL)) {
> +		err = true;
> +	}
> +
> +	/* wait for thread startup */
> +	while (!logq_running)
> +		pthread_cond_wait(&logev_cond, &logev_lock);
> +	pthread_cleanup_pop(1);
> +
> +	if (err) {
>  		fprintf(stderr,"can't start log thread\n");
>  		exit(1);
>  	}
> @@ -112,27 +139,26 @@ void log_thread_reset (void)
>  
>  void log_thread_stop (void)
>  {
> +	int running;
> +
>  	if (!la)
>  		return;
>  
>  	logdbg(stderr,"enter log_thread_stop\n");
>  
>  	pthread_mutex_lock(&logev_lock);
> -	logq_running = 0;
> -	pthread_cond_signal(&logev_cond);
> -	pthread_mutex_unlock(&logev_lock);
> -
> -	pthread_mutex_lock(&logq_lock);
> -	pthread_cancel(log_thr);
> -	pthread_mutex_unlock(&logq_lock);
> -	pthread_join(log_thr, NULL);
> -	log_thr = (pthread_t)0;
> +	pthread_cleanup_push(cleanup_mutex, &logev_lock);
> +	running = logq_running;
> +	if (running) {
> +		pthread_cancel(log_thr);
> +		pthread_cond_signal(&logev_cond);
> +	}
> +	pthread_cleanup_pop(1);
>  
> -	flush_logqueue();
> +	if (running)
> +		pthread_join(log_thr, NULL);
>  
> -	pthread_mutex_destroy(&logq_lock);
> -	pthread_mutex_destroy(&logev_lock);
> -	pthread_cond_destroy(&logev_cond);
>  
> +	flush_logqueue();
>  	log_close();
>  }
> -- 
> 2.28.0

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Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-16 10:44 [dm-devel] [PATCH v2 00/29] libmultipath: improve cleanup on exit mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 01/29] multipathd: uxlsnr: avoid deadlock " mwilck
2020-10-20 19:04   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 02/29] multipathd: Fix liburcu memory leak mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 03/29] multipathd: move handling of io_err_stat_attr into libmultipath mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 04/29] multipathd: move vecs desctruction into cleanup function mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 05/29] multipathd: make some globals static mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 06/29] multipathd: move threads destruction into separate function mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 07/29] multipathd: move conf " mwilck
2020-10-19 18:56   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 08/29] multipathd: move pid " mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 09/29] multipathd: close pidfile on exit mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 10/29] multipathd: add helper for systemd notification at exit mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 11/29] multipathd: child(): call cleanups in failure case, too mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 12/29] multipathd: unwatch_all_dmevents: check if waiter is initialized mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 13/29] multipathd: print error message if config can't be loaded mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 14/29] libmultipath: add libmp_dm_exit() mwilck
2020-10-19 19:07   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 15/29] multipathd: fixup libdm deinitialization mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 16/29] libmultipath: log_thread_stop(): check if logarea is initialized mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 17/29] multipathd: add cleanup_child() exit handler mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 18/29] libmultipath: fix log_thread startup and teardown mwilck
2020-10-19 20:00   ` Benjamin Marzinski [this message]
2020-10-26 13:58     ` Martin Wilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 19/29] multipathd: move cleanup_{prio, checkers, foreign} to libmultipath_exit mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 20/29] multipath: use atexit() for cleanup handlers mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 21/29] mpathpersist: " mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 22/29] multipath: fix leaks in check_path_valid() mwilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 23/29] multipath-tools: mpath-tools.supp: file with valgrind suppressions mwilck
2020-10-19 20:01   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 24/29] libmultipath: use libmp_verbosity to track verbosity mwilck
2020-10-19 20:38   ` Benjamin Marzinski
2020-10-26 14:47     ` Martin Wilck
2020-10-16 10:44 ` [dm-devel] [PATCH v2 25/29] libmultipath: introduce symbolic values for logsink mwilck
2020-10-16 20:13   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 26/29] libmultipath: simplify dlog() mwilck
2020-10-19 21:07   ` Benjamin Marzinski
2020-10-16 10:44 ` [dm-devel] [PATCH v2 27/29] multipathd: common code for "-k" and command args mwilck
2020-10-19 21:51   ` Benjamin Marzinski
2020-10-16 10:45 ` [dm-devel] [PATCH v2 28/29] multipathd: sanitize uxsock_listen() mwilck
2020-10-19 23:33   ` Benjamin Marzinski
2020-10-26 13:54     ` Martin Wilck
2020-10-16 10:45 ` [dm-devel] [PATCH v2 29/29] libmultipath: fix race between log_safe and log_thread_stop() mwilck
2020-10-20  2:20   ` Benjamin Marzinski
2020-10-26 16:22     ` Martin Wilck
2020-10-26 17:24       ` Martin Wilck
2020-11-03  0:11         ` Benjamin Marzinski
2020-11-04 12:36           ` Martin Wilck
2020-11-04 15:46             ` Benjamin Marzinski

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