On Wed, Dec 16, 2020 at 07:16:57PM +0100, mwi...@suse.com wrote:
> From: Martin Wilck <mwi...@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 to just cancel
> and join it. Third, the locking wasn't cancel-safe in some places. Forth,
> log_thread_start() didn't wait for startup 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.
>
Reviewed-by: Benjamin Marzinski <bmarz...@redhat.com>
> Signed-off-by: Martin Wilck <mwi...@suse.com>
> ---
> libmultipath/log_pthread.c | 62 +++++++++++++++++++++++++++-----------
> 1 file changed, 45 insertions(+), 17 deletions(-)
>
> diff --git a/libmultipath/log_pthread.c b/libmultipath/log_pthread.c
> index 0c327ff..3a2566a 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;
>
> @@ -56,35 +57,52 @@ 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");
> + int running = 0;
>
> + logdbg(stderr,"enter log_thread_start\n");
> pthread_mutex_init(&logq_lock, NULL);
> pthread_mutex_init(&logev_lock, NULL);
> pthread_cond_init(&logev_cond, NULL);
> @@ -93,7 +111,15 @@ void log_thread_start (pthread_attr_t *attr)
> fprintf(stderr,"can't initialize log buffer\n");
> exit(1);
> }
> - if (pthread_create(&log_thr, attr, log_thread, NULL)) {
> +
> + pthread_mutex_lock(&logev_lock);
> + pthread_cleanup_push(cleanup_mutex, &logev_lock);
> + if (!pthread_create(&log_thr, attr, log_thread, NULL))
> + while (!(running = logq_running))
> + pthread_cond_wait(&logev_cond, &logev_lock);
> + pthread_cleanup_pop(1);
> +
> + if (!running) {
> fprintf(stderr,"can't start log thread\n");
> exit(1);
> }
> @@ -112,23 +138,25 @@ 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);
> --
> 2.29.0
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