svn commit: r360897 - in stable/12: lib/libc/sys sys/kern

[Mark Johnston]

Author: markj
Date: Mon May 11 15:20:40 2020
New Revision: 360897
URL: https://svnweb.freebsd.org/changeset/base/360897

Log:
  MFC r360380:
  Fix handling of EV_EOF for named pipes.
  
  PR:	203366, 224615, 246350

Modified:
  stable/12/lib/libc/sys/kqueue.2
  stable/12/sys/kern/sys_pipe.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/lib/libc/sys/kqueue.2
==============================================================================
--- stable/12/lib/libc/sys/kqueue.2	Mon May 11 15:20:05 2020	(r360896)
+++ stable/12/lib/libc/sys/kqueue.2	Mon May 11 15:20:40 2020	(r360897)
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd April 21, 2020
+.Dd April 27, 2020
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -323,8 +323,7 @@ When the last writer disconnects, the filter will set
 .Dv EV_EOF
 in
 .Va flags .
-This may be cleared by passing in
-.Dv EV_CLEAR ,
+This will be cleared by the filter when a new writer connects,
 at which point the
 filter will resume waiting for data to become available before
 returning.
@@ -343,9 +342,10 @@ For sockets, pipes
 and fifos,
 .Va data
 will contain the amount of space remaining in the write buffer.
-The filter will set EV_EOF when the reader disconnects, and for
-the fifo case, this may be cleared by use of
-.Dv EV_CLEAR .
+The filter will set
+.Dv EV_EOF
+when the reader disconnects, and for the fifo case, this will be cleared
+when a new reader connects.
 Note that this filter is not supported for vnodes or BPF devices.
 .Pp
 For sockets, the low water mark and socket error handling is

Modified: stable/12/sys/kern/sys_pipe.c
==============================================================================
--- stable/12/sys/kern/sys_pipe.c	Mon May 11 15:20:05 2020	(r360896)
+++ stable/12/sys/kern/sys_pipe.c	Mon May 11 15:20:40 2020	(r360897)
@@ -826,7 +826,12 @@ unlocked_error:
 		}
 	}
 
-	if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) >= PIPE_BUF)
+	/*
+	 * Only wake up writers if there was actually something read.
+	 * Otherwise, when calling read(2) at EOF, a spurious wakeup occurs.
+	 */
+	if (nread > 0 &&
+	    rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt >= PIPE_BUF)
 		pipeselwakeup(rpipe);
 
 	PIPE_UNLOCK(rpipe);
@@ -1728,48 +1733,54 @@ filt_pipedetach(struct knote *kn)
 static int
 filt_piperead(struct knote *kn, long hint)
 {
+	struct file *fp = kn->kn_fp;
 	struct pipe *rpipe = kn->kn_hook;
-	struct pipe *wpipe = rpipe->pipe_peer;
-	int ret;
 
 	PIPE_LOCK_ASSERT(rpipe, MA_OWNED);
 	kn->kn_data = rpipe->pipe_buffer.cnt;
 	if (kn->kn_data == 0)
 		kn->kn_data = rpipe->pipe_map.cnt;
 
-	if ((rpipe->pipe_state & PIPE_EOF) ||
-	    wpipe->pipe_present != PIPE_ACTIVE ||
-	    (wpipe->pipe_state & PIPE_EOF)) {
+	if ((rpipe->pipe_state & PIPE_EOF) != 0 &&
+	    ((rpipe->pipe_state & PIPE_NAMED) == 0 ||
+	    fp->f_pipegen != rpipe->pipe_wgen)) {
 		kn->kn_flags |= EV_EOF;
 		return (1);
 	}
-	ret = kn->kn_data > 0;
-	return ret;
+	kn->kn_flags &= ~EV_EOF;
+	return (kn->kn_data > 0);
 }
 
 /*ARGSUSED*/
 static int
 filt_pipewrite(struct knote *kn, long hint)
 {
-	struct pipe *wpipe;
+	struct pipe *wpipe = kn->kn_hook;
 
 	/*
 	 * If this end of the pipe is closed, the knote was removed from the
 	 * knlist and the list lock (i.e., the pipe lock) is therefore not held.
 	 */
-	wpipe = kn->kn_hook;
+	if (wpipe->pipe_present == PIPE_ACTIVE ||
+	    (wpipe->pipe_state & PIPE_NAMED) != 0) {
+		PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
+
+		if (wpipe->pipe_state & PIPE_DIRECTW) {
+			kn->kn_data = 0;
+		} else if (wpipe->pipe_buffer.size > 0) {
+			kn->kn_data = wpipe->pipe_buffer.size -
+			    wpipe->pipe_buffer.cnt;
+		} else {
+			kn->kn_data = PIPE_BUF;
+		}
+	}
+
 	if (wpipe->pipe_present != PIPE_ACTIVE ||
 	    (wpipe->pipe_state & PIPE_EOF)) {
-		kn->kn_data = 0;
 		kn->kn_flags |= EV_EOF;
 		return (1);
 	}
-	PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
-	kn->kn_data = (wpipe->pipe_buffer.size > 0) ?
-	    (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) : PIPE_BUF;
-	if (wpipe->pipe_state & PIPE_DIRECTW)
-		kn->kn_data = 0;
-
+	kn->kn_flags &= ~EV_EOF;
 	return (kn->kn_data >= PIPE_BUF);
 }