On Thu, Sep 24, 2020 at 03:40:49PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> 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). Finally,
> pthread_cancel() was called under logq_lock, which doesn't make sense to
> me at all.
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> libmultipath/log_pthread.c | 59 ++++++++++++++++++++++++++++----------
> 1 file changed, 44 insertions(+), 15 deletions(-)
>
> diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c
> index 0c327ff..5825e66 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;
>
> @@ -56,28 +57,45 @@ 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_cond_signal(&logev_cond);
> + 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;
> }
>
> @@ -98,6 +116,12 @@ void log_thread_start (pthread_attr_t *attr)
> exit(1);
> }
>
> + pthread_mutex_lock(&logev_lock);
> + pthread_cleanup_push(cleanup_mutex, &logev_lock);
> + /* wait for thread startup */
> + while (!logq_running)
> + pthread_cond_wait(&logev_cond, &logev_lock);
> + pthread_cleanup_pop(1);
> return;
> }
>
> @@ -112,21 +136,26 @@ 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_cleanup_push(cleanup_mutex, &logev_lock);
> + running = logq_running;
> + if (running) {
> + pthread_cancel(log_thr);
> + pthread_cond_signal(&logev_cond);
> + }
> + while (logq_running)
> + pthread_cond_wait(&logev_cond, &logev_lock);
If we're already going to join the thread, why do we have to wait for
the cleanup handler first? Won't the join do the waiting we need?
-Ben
> + pthread_cleanup_pop(1);
> +
> + if (running)
> + pthread_join(log_thr, NULL);
>
> - pthread_mutex_lock(&logq_lock);
> - pthread_cancel(log_thr);
> - pthread_mutex_unlock(&logq_lock);
> - pthread_join(log_thr, NULL);
> - log_thr = (pthread_t)0;
>
> flush_logqueue();
>
> --
> 2.28.0
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