| Message ID | 20200924134054.14632-19-mwilck@suse.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | christophe varoqui |
| Headers | show |
| Series | libmultipath: improve cleanup on exit | expand |
On Thu, Sep 24, 2020 at 03:40:49PM +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). Finally, > 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 | 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 -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
On Mon, 2020-09-28 at 15:15 -0500, Benjamin Marzinski wrote: > On Thu, Sep 24, 2020 at 03:40:49PM +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). Finally, > > pthread_cancel() was called under logq_lock, which doesn't make > > sense to > > me at all. > > > > Signed-off-by: Martin Wilck <mwilck@suse.com> > > --- > > > > 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? Yes, I guess it would. I implemented it in a way analogous the startup sequence, but it's really not necessary for shutdown. Thanks for pointing it out. Martin -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
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); + 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();