pipe: allow for lockless pipe_stat

pipes get stated all thet time and this avoidably contributed to contention.
The pipe lock is only held to accomodate MAC and to check the type.

Since normally there is no probe for pipe stat depessimize this by having the
flag.

The pipe_state field gets modified with locks held all the time and it's not
feasible to convert them to use atomic store. Move the type flag away to a
separate variable as a simple cleanup and to provide stable field to read.
Use short for both fields to avoid growing the struct.

While here short-circuit MAC for pipe_poll as well.

1 files changed, 16 insertions, 17 deletions

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index 38b26c8e28f3..6940bbf3fa1f 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -140,7 +140,7 @@ __FBSDID("$FreeBSD$");
 /* #define PIPE_NODIRECT */
 
 #define PIPE_PEER(pipe)	\
-	(((pipe)->pipe_state & PIPE_NAMED) ? (pipe) : ((pipe)->pipe_peer))
+	(((pipe)->pipe_type & PIPE_TYPE_NAMED) ? (pipe) : ((pipe)->pipe_peer))
 
 /*
  * interfaces to the outside world
@@ -403,7 +403,7 @@ pipe_named_ctor(struct pipe **ppipe, struct thread *td)
 	error = pipe_paircreate(td, &pp);
 	if (error != 0)
 		return (error);
-	pp->pp_rpipe.pipe_state |= PIPE_NAMED;
+	pp->pp_rpipe.pipe_type |= PIPE_TYPE_NAMED;
 	*ppipe = &pp->pp_rpipe;
 	return (0);
 }
@@ -413,7 +413,7 @@ pipe_dtor(struct pipe *dpipe)
 {
 	struct pipe *peer;
 
-	peer = (dpipe->pipe_state & PIPE_NAMED) != 0 ? dpipe->pipe_peer : NULL;
+	peer = (dpipe->pipe_type & PIPE_TYPE_NAMED) != 0 ? dpipe->pipe_peer : NULL;
 	funsetown(&dpipe->pipe_sigio);
 	pipeclose(dpipe);
 	if (peer != NULL) {
@@ -1328,7 +1328,7 @@ pipe_truncate(struct file *fp, off_t length, struct ucred *active_cred,
 	int error;
 
 	cpipe = fp->f_data;
-	if (cpipe->pipe_state & PIPE_NAMED)
+	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
 		error = vnops.fo_truncate(fp, length, active_cred, td);
 	else
 		error = invfo_truncate(fp, length, active_cred, td);
@@ -1443,7 +1443,7 @@ pipe_poll(struct file *fp, int events, struct ucred *active_cred,
 
 	levents = events &
 	    (POLLIN | POLLINIGNEOF | POLLPRI | POLLRDNORM | POLLRDBAND);
-	if (rpipe->pipe_state & PIPE_NAMED && fp->f_flag & FREAD && levents &&
+	if (rpipe->pipe_type & PIPE_TYPE_NAMED && fp->f_flag & FREAD && levents &&
 	    fp->f_pipegen == rpipe->pipe_wgen)
 		events |= POLLINIGNEOF;
 
@@ -1496,23 +1496,22 @@ pipe_stat(struct file *fp, struct stat *ub, struct ucred *active_cred,
 #endif
 
 	pipe = fp->f_data;
-	PIPE_LOCK(pipe);
 #ifdef MAC
-	error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
-	if (error) {
+	if (mac_pipe_check_stat_enabled()) {
+		PIPE_LOCK(pipe);
+		error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
 		PIPE_UNLOCK(pipe);
-		return (error);
+		if (error) {
+			return (error);
+		}
 	}
 #endif
 
 	/* For named pipes ask the underlying filesystem. */
-	if (pipe->pipe_state & PIPE_NAMED) {
-		PIPE_UNLOCK(pipe);
+	if (pipe->pipe_type & PIPE_TYPE_NAMED) {
 		return (vnops.fo_stat(fp, ub, active_cred, td));
 	}
 
-	PIPE_UNLOCK(pipe);
-
 	bzero(ub, sizeof(*ub));
 	ub->st_mode = S_IFIFO;
 	ub->st_blksize = PAGE_SIZE;
@@ -1554,7 +1553,7 @@ pipe_chmod(struct file *fp, mode_t mode, struct ucred *active_cred, struct threa
 	int error;
 
 	cpipe = fp->f_data;
-	if (cpipe->pipe_state & PIPE_NAMED)
+	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
 		error = vn_chmod(fp, mode, active_cred, td);
 	else
 		error = invfo_chmod(fp, mode, active_cred, td);
@@ -1569,7 +1568,7 @@ pipe_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
 	int error;
 
 	cpipe = fp->f_data;
-	if (cpipe->pipe_state & PIPE_NAMED)
+	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
 		error = vn_chown(fp, uid, gid, active_cred, td);
 	else
 		error = invfo_chown(fp, uid, gid, active_cred, td);
@@ -1758,7 +1757,7 @@ filt_piperead(struct knote *kn, long hint)
 		kn->kn_data = rpipe->pipe_pages.cnt;
 
 	if ((rpipe->pipe_state & PIPE_EOF) != 0 &&
-	    ((rpipe->pipe_state & PIPE_NAMED) == 0 ||
+	    ((rpipe->pipe_type & PIPE_TYPE_NAMED) == 0 ||
 	    fp->f_pipegen != rpipe->pipe_wgen)) {
 		kn->kn_flags |= EV_EOF;
 		return (1);
@@ -1778,7 +1777,7 @@ filt_pipewrite(struct knote *kn, long hint)
 	 * knlist and the list lock (i.e., the pipe lock) is therefore not held.
 	 */
 	if (wpipe->pipe_present == PIPE_ACTIVE ||
-	    (wpipe->pipe_state & PIPE_NAMED) != 0) {
+	    (wpipe->pipe_type & PIPE_TYPE_NAMED) != 0) {
 		PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
 
 		if (wpipe->pipe_state & PIPE_DIRECTW) {