Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote:
> On 2022-09-22 05:15, Eric Wong via lttng-dev wrote:
> > Hello, I'm using urcu-bp + rculfhash + call_rcu to implement
> > malloc instrumentation (via LD_PRELOAD) on an existing
> > single-threaded Perl codebase which uses Linux signalfd.
> >
> > signalfd depends on signals being blocked in all threads
> > of the process, otherwise threads with unblocked signals
> > can receive them and starve the signalfd.
> >
> > While some threads in URCU do block signals (e.g. workqueue
> > worker for rculfhash), the call_rcu thread and rculfhash
> > partition_resize_helper threads do not...
> >
> > Should all threads URCU creates block signals (aside from SIGRCU)?
>
> Yes, I think you are right. The SIGRCU signal is only needed for the
> urcu-signal flavor though.
>
> Would you like to submit a patch ?
Sure.
Is there a way to detect at runtime when urcu-signal is in use
so SIGRCU (SIGUSR1) doesn't get unblocked when using other flavors?
I actually use SIGUSR1 in my signalfd-using codebase.
I also want to remove cds_lfht_worker_init entirely since it's racy.
Signal blocking needs to be done in the parent before pthread_create
to avoid a window where the child has unblocked signals.
Thanks. Anyways, this is my work-in-progress:
diff --git a/src/rculfhash.c b/src/rculfhash.c
index 7c0b9fb..5f455af 100644
--- a/src/rculfhash.c
+++ b/src/rculfhash.c
@@ -1251,6 +1251,7 @@ void partition_resize_helper(struct cds_lfht *ht,
unsigned long i,
struct partition_resize_work *work;
int ret;
unsigned long thread, nr_threads;
+ sigset_t newmask, oldmask;
urcu_posix_assert(nr_cpus_mask != -1);
if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD)
@@ -1273,6 +1274,12 @@ void partition_resize_helper(struct cds_lfht *ht,
unsigned long i,
dbg_printf("error allocating for resize, single-threading\n");
goto fallback;
}
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
+
for (thread = 0; thread < nr_threads; thread++) {
work[thread].ht = ht;
work[thread].i = i;
@@ -1294,6 +1301,10 @@ void partition_resize_helper(struct cds_lfht *ht,
unsigned long i,
}
urcu_posix_assert(!ret);
}
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ urcu_posix_assert(!ret);
+
for (thread = 0; thread < nr_threads; thread++) {
ret = pthread_join(work[thread].thread_id, NULL);
urcu_posix_assert(!ret);
diff --git a/src/urcu-call-rcu-impl.h b/src/urcu-call-rcu-impl.h
index e9366b4..9f85d55 100644
--- a/src/urcu-call-rcu-impl.h
+++ b/src/urcu-call-rcu-impl.h
@@ -434,6 +434,7 @@ static void call_rcu_data_init(struct call_rcu_data **crdpp,
{
struct call_rcu_data *crdp;
int ret;
+ sigset_t newmask, oldmask;
crdp = malloc(sizeof(*crdp));
if (crdp == NULL)
@@ -448,9 +449,18 @@ static void call_rcu_data_init(struct call_rcu_data
**crdpp,
crdp->gp_count = 0;
cmm_smp_mb(); /* Structure initialized before pointer is planted. */
*crdpp = crdp;
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
+
ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
if (ret)
urcu_die(ret);
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ urcu_posix_assert(!ret);
}
/*
diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
index b5d7926..1c96287 100644
--- a/src/urcu-defer-impl.h
+++ b/src/urcu-defer-impl.h
@@ -409,9 +409,18 @@ void defer_rcu(void (*fct)(void *p), void *p)
static void start_defer_thread(void)
{
int ret;
+ sigset_t newmask, oldmask;
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
urcu_posix_assert(!ret);
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ urcu_posix_assert(!ret);
}
static void stop_defer_thread(void)
diff --git a/src/workqueue.c b/src/workqueue.c
index b6361ad..1039d72 100644
--- a/src/workqueue.c
+++ b/src/workqueue.c
@@ -284,6 +284,7 @@ struct urcu_workqueue *urcu_workqueue_create(unsigned long
flags,
{
struct urcu_workqueue *workqueue;
int ret;
+ sigset_t newmask, oldmask;
workqueue = malloc(sizeof(*workqueue));
if (workqueue == NULL)
@@ -304,10 +305,20 @@ struct urcu_workqueue *urcu_workqueue_create(unsigned
long flags,
workqueue->cpu_affinity = cpu_affinity;
workqueue->loop_count = 0;
cmm_smp_mb(); /* Structure initialized before pointer is planted. */
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
+
ret = pthread_create(&workqueue->tid, NULL, workqueue_thread,
workqueue);
if (ret) {
urcu_die(ret);
}
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ urcu_posix_assert(!ret);
+
return workqueue;
}
@@ -464,13 +475,23 @@ void urcu_workqueue_resume_worker(struct urcu_workqueue
*workqueue)
void urcu_workqueue_create_worker(struct urcu_workqueue *workqueue)
{
int ret;
+ sigset_t newmask, oldmask;
/* Clear workqueue state from parent. */
workqueue->flags &= ~URCU_WORKQUEUE_PAUSED;
workqueue->flags &= ~URCU_WORKQUEUE_PAUSE;
workqueue->tid = 0;
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
+
ret = pthread_create(&workqueue->tid, NULL, workqueue_thread,
workqueue);
if (ret) {
urcu_die(ret);
}
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ urcu_posix_assert(!ret);
}
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