[hurd,commited,2/2] htl: Make sem_*wait cancellations points

Message ID 20200623232024.2229631-3-samuel.thibault@ens-lyon.org
State New
Headers show
Series
  • Make sem_*wait cancellations points
Related show

Commit Message

Samuel Thibault June 23, 2020, 11:20 p.m.
By aligning its implementation on pthread_cond_wait.

* sysdeps/htl/sem-timedwait.c (cancel_ctx): New structure.
(cancel_hook): New function.
(__sem_timedwait_internal): Check for cancellation and register
cancellation hook that wakes the thread up, and check again for
cancellation on exit.
* nptl/tst-cancel13.c, nptl/tst-cancelx13.c: Move to...
* sysdeps/pthread/: ... here.
* nptl/Makefile: Move corresponding references and rules to...
* sysdeps/pthread/Makefile: ... here.
---
 nptl/Makefile                             |  4 +-
 sysdeps/htl/sem-timedwait.c               | 92 +++++++++++++++++++++--
 sysdeps/pthread/Makefile                  |  9 ++-
 {nptl => sysdeps/pthread}/tst-cancel13.c  |  0
 {nptl => sysdeps/pthread}/tst-cancelx13.c |  0
 5 files changed, 90 insertions(+), 15 deletions(-)
 rename {nptl => sysdeps/pthread}/tst-cancel13.c (100%)
 rename {nptl => sysdeps/pthread}/tst-cancelx13.c (100%)

-- 
2.27.0

Patch

diff --git a/nptl/Makefile b/nptl/Makefile
index 24ebd07a30..4602824bf1 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -278,7 +278,7 @@  tests = tst-attr2 tst-attr3 tst-default-attr \
 	tst-sem17 \
 	tst-tsd3 tst-tsd4 \
 	tst-cancel4 tst-cancel4_1 tst-cancel4_2 tst-cancel5 \
-	tst-cancel7 tst-cancel13 \
+	tst-cancel7 \
 	tst-cancel16 tst-cancel17 tst-cancel20 tst-cancel24 \
 	tst-cleanup4 \
 	tst-signal3 \
@@ -358,7 +358,6 @@  endif
 LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
 
 tests += tst-cancelx4 tst-cancelx5 tst-cancelx7 \
-	 tst-cancelx13 \
 	 tst-cancelx16 tst-cancelx17 tst-cancelx20 \
 	 tst-cleanupx4
 
@@ -477,7 +476,6 @@  CFLAGS-tst-cancelx5.c += -Wno-error
 CFLAGS-tst-cancelx4.c += -fexceptions
 CFLAGS-tst-cancelx5.c += -fexceptions
 CFLAGS-tst-cancelx7.c += -fexceptions
-CFLAGS-tst-cancelx13.c += -fexceptions
 CFLAGS-tst-cancelx16.c += -fexceptions
 CFLAGS-tst-cancelx17.c += -fexceptions
 CFLAGS-tst-cancelx20.c += -fexceptions -fasynchronous-unwind-tables
diff --git a/sysdeps/htl/sem-timedwait.c b/sysdeps/htl/sem-timedwait.c
index 0b1b6d0961..691fb7e5ee 100644
--- a/sysdeps/htl/sem-timedwait.c
+++ b/sysdeps/htl/sem-timedwait.c
@@ -23,36 +23,98 @@ 
 
 #include <pt-internal.h>
 
+struct cancel_ctx
+{
+  struct __pthread *wakeup;
+  sem_t *sem;
+};
+
+static void
+cancel_hook (void *arg)
+{
+  struct cancel_ctx *ctx = arg;
+  struct __pthread *wakeup = ctx->wakeup;
+  sem_t *sem = ctx->sem;
+  int unblock;
+
+  __pthread_spin_wait (&sem->__lock);
+  /* The thread only needs to be awaken if it's blocking or about to block.
+     If it was already unblocked, it's not queued any more.  */
+  unblock = wakeup->prevp != NULL;
+  if (unblock)
+    __pthread_dequeue (wakeup);
+  __pthread_spin_unlock (&sem->__lock);
+
+  if (unblock)
+    __pthread_wakeup (wakeup);
+}
+
 int
 __sem_timedwait_internal (sem_t *restrict sem,
 			  clockid_t clock_id,
 			  const struct timespec *restrict timeout)
 {
   error_t err;
-  int drain;
-  struct __pthread *self;
+  int cancelled, oldtype, drain;
+  int ret = 0;
+
+  struct __pthread *self = _pthread_self ();
+  struct cancel_ctx ctx;
+  ctx.wakeup = self;
+  ctx.sem = sem;
+
+  /* Test for a pending cancellation request, switch to deferred mode for
+     safer resource handling, and prepare the hook to call in case we're
+     cancelled while blocking.  Once CANCEL_LOCK is released, the cancellation
+     hook can be called by another thread at any time.  Whatever happens,
+     this function must exit with MUTEX locked.
+
+     This function contains inline implementations of pthread_testcancel and
+     pthread_setcanceltype to reduce locking overhead.  */
+  __pthread_mutex_lock (&self->cancel_lock);
+  cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
+      && self->cancel_pending;
+
+  if (cancelled)
+    {
+      __pthread_mutex_unlock (&self->cancel_lock);
+      __pthread_exit (PTHREAD_CANCELED);
+    }
+
+  self->cancel_hook = cancel_hook;
+  self->cancel_hook_arg = &ctx;
+  oldtype = self->cancel_type;
 
+  if (oldtype != PTHREAD_CANCEL_DEFERRED)
+    self->cancel_type = PTHREAD_CANCEL_DEFERRED;
+
+  /* Add ourselves to the list of waiters.  This is done while setting
+     the cancellation hook to simplify the cancellation procedure, i.e.
+     if the thread is queued, it can be cancelled, otherwise it is
+     already unblocked, progressing on the return path.  */
   __pthread_spin_wait (&sem->__lock);
   if (sem->__value > 0)
     /* Successful down.  */
     {
       sem->__value--;
       __pthread_spin_unlock (&sem->__lock);
-      return 0;
+      goto out_locked;
     }
 
   if (timeout != NULL && ! valid_nanoseconds (timeout->tv_nsec))
     {
       errno = EINVAL;
-      return -1;
+      ret = -1;
+      __pthread_spin_unlock (&sem->__lock);
+      goto out_locked;
     }
 
   /* Add ourselves to the queue.  */
-  self = _pthread_self ();
-
   __pthread_enqueue (&sem->__queue, self);
   __pthread_spin_unlock (&sem->__lock);
 
+  __pthread_mutex_unlock (&self->cancel_lock);
+
   /* Block the thread.  */
   if (timeout != NULL)
     err = __pthread_timedblock_intr (self, timeout, clock_id);
@@ -82,10 +144,24 @@  __sem_timedwait_internal (sem_t *restrict sem,
     {
       assert (err == ETIMEDOUT || err == EINTR);
       errno = err;
-      return -1;
+      ret = -1;
     }
 
-  return 0;
+  /* We're almost done.  Remove the unblock hook, restore the previous
+     cancellation type, and check for a pending cancellation request.  */
+  __pthread_mutex_lock (&self->cancel_lock);
+out_locked:
+  self->cancel_hook = NULL;
+  self->cancel_hook_arg = NULL;
+  self->cancel_type = oldtype;
+  cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
+      && self->cancel_pending;
+  __pthread_mutex_unlock (&self->cancel_lock);
+
+  if (cancelled)
+    __pthread_exit (PTHREAD_CANCELED);
+
+  return ret;
 }
 
 int
diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 01602e69d5..ed31ae8f4f 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -55,8 +55,8 @@  tests += tst-cnd-basic tst-mtx-trylock tst-cnd-broadcast \
 	 tst-cancel-self-canceltype tst-cancel-self-testcancel \
 	 tst-cancel1 tst-cancel2 tst-cancel3 \
 	 tst-cancel6 tst-cancel8 tst-cancel9 tst-cancel10 tst-cancel11 \
-	 tst-cancel12 tst-cancel14 tst-cancel15 tst-cancel18 tst-cancel19 \
-	 tst-cancel21 \
+	 tst-cancel12 tst-cancel13 tst-cancel14 tst-cancel15 tst-cancel18 \
+	 tst-cancel19 tst-cancel21 \
 	 tst-cancel22 tst-cancel23 tst-cancel26 tst-cancel27 tst-cancel28 \
 	 tst-cleanup0 tst-cleanup1 tst-cleanup2 tst-cleanup3 \
 	 tst-clock1 \
@@ -117,8 +117,8 @@  CFLAGS-tst-cleanup2.c += -fno-builtin
 CFLAGS-tst-cleanupx2.c += -fno-builtin
 
 tests += tst-cancelx2 tst-cancelx3 tst-cancelx6 tst-cancelx8 tst-cancelx9 \
-	 tst-cancelx10 tst-cancelx11 tst-cancelx12 tst-cancelx14 tst-cancelx15 \
-	 tst-cancelx18 tst-cancelx21 \
+	 tst-cancelx10 tst-cancelx11 tst-cancelx12 tst-cancelx13 tst-cancelx14 \
+	 tst-cancelx15 tst-cancelx18 tst-cancelx21 \
 	 tst-cleanupx0 tst-cleanupx1 tst-cleanupx2 tst-cleanupx3
 
 ifeq ($(build-shared),yes)
@@ -160,6 +160,7 @@  CFLAGS-tst-cancelx9.c += -fexceptions
 CFLAGS-tst-cancelx10.c += -fexceptions
 CFLAGS-tst-cancelx11.c += -fexceptions
 CFLAGS-tst-cancelx12.c += -fexceptions
+CFLAGS-tst-cancelx13.c += -fexceptions
 CFLAGS-tst-cancelx14.c += -fexceptions
 CFLAGS-tst-cancelx15.c += -fexceptions
 CFLAGS-tst-cancelx18.c += -fexceptions
diff --git a/nptl/tst-cancel13.c b/sysdeps/pthread/tst-cancel13.c
similarity index 100%
rename from nptl/tst-cancel13.c
rename to sysdeps/pthread/tst-cancel13.c
diff --git a/nptl/tst-cancelx13.c b/sysdeps/pthread/tst-cancelx13.c
similarity index 100%
rename from nptl/tst-cancelx13.c
rename to sysdeps/pthread/tst-cancelx13.c