The pipe_poll() performs lockless access to the vnode to test

fifo_iseof() condition, allowing the v_fifoinfo to be reset and freed
by fifo_cleanup().

Precalculate EOF at the places were fo_wgen is changed, and cache the
state in a new pipe state flag PIPE_SAMEWGEN.

Reported and tested by:	bf
Submitted by:	gianni
MFC after:	1 week (a backport)

4 files changed, 14 insertions, 15 deletions

diff --git a/sys/fs/fifofs/fifo.h b/sys/fs/fifofs/fifo.h
index 94bccc6..da85ae2 100644
--- a/sys/fs/fifofs/fifo.h
+++ b/sys/fs/fifofs/fifo.h
@@ -33,7 +33,6 @@
 /*
  * Prototypes for fifo operations on vnodes.
  */
-int	fifo_iseof(struct file *);
 int	fifo_vnoperate(struct vop_generic_args *);
 int	fifo_printinfo(struct vnode *);
 
diff --git a/sys/fs/fifofs/fifo_vnops.c b/sys/fs/fifofs/fifo_vnops.c
index 1cc17cf..65c44ae 100644
--- a/sys/fs/fifofs/fifo_vnops.c
+++ b/sys/fs/fifofs/fifo_vnops.c
@@ -67,8 +67,16 @@ struct fifoinfo {
 	long	fi_readers;
 	long	fi_writers;
 	int	fi_wgen;
+	int	fi_seqcount;
 };
 
+#define FIFO_UPDWGEN(fip, pip)	do { \
+	if ((fip)->fi_wgen == (fip)->fi_seqcount) 			\
+		(pip)->pipe_state |= PIPE_SAMEWGEN;			\
+	else								\
+		(pip)->pipe_state &= ~PIPE_SAMEWGEN;			\
+} while (0)
+
 static vop_print_t	fifo_print;
 static vop_open_t	fifo_open;
 static vop_close_t	fifo_close;
@@ -174,7 +182,8 @@ fifo_open(ap)
 			if (fip->fi_writers > 0)
 				wakeup(&fip->fi_writers);
 		}
-		fp->f_seqcount = fip->fi_wgen - fip->fi_writers;
+		fip->fi_seqcount = fip->fi_wgen - fip->fi_writers;
+		FIFO_UPDWGEN(fip, fpipe);
 	}
 	if (ap->a_mode & FWRITE) {
 		if ((ap->a_mode & O_NONBLOCK) && fip->fi_readers == 0) {
@@ -228,6 +237,7 @@ fifo_open(ap)
 					if (fpipe->pipe_state & PIPE_WANTR)
 						wakeup(fpipe);
 					fip->fi_wgen++;
+					FIFO_UPDWGEN(fip, fpipe);
 					PIPE_UNLOCK(fpipe);
 					fifo_cleanup(vp);
 				}
@@ -287,6 +297,7 @@ fifo_close(ap)
 			if (cpipe->pipe_state & PIPE_WANTR)
 				wakeup(cpipe);
 			fip->fi_wgen++;
+			FIFO_UPDWGEN(fip, cpipe);
 			PIPE_UNLOCK(cpipe);
 		}
 	}
@@ -373,15 +384,3 @@ fifo_advlock(ap)
 	return (ap->a_flags & F_FLOCK ? EOPNOTSUPP : EINVAL);
 }
 
-int
-fifo_iseof(struct file *fp)
-{
-	struct fifoinfo *fip;
-
-	KASSERT(fp->f_vnode != NULL, ("fifo_iseof: no vnode info"));
-	KASSERT(fp->f_vnode->v_fifoinfo != NULL, ("fifo_iseof: no fifoinfo"));
-	fip = fp->f_vnode->v_fifoinfo;
-	PIPE_LOCK_ASSERT(fip->fi_pipe, MA_OWNED);
-	return (fp->f_seqcount == fip->fi_wgen);
-}
-
diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index 89b9589..e973c22 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -1430,7 +1430,7 @@ pipe_poll(fp, events, active_cred, td)
 	levents = events &
 	    (POLLIN | POLLINIGNEOF | POLLPRI | POLLRDNORM | POLLRDBAND);
 	if (rpipe->pipe_state & PIPE_NAMED && fp->f_flag & FREAD && levents &&
-	    fifo_iseof(fp))
+	    rpipe->pipe_state & PIPE_SAMEWGEN)
 		events |= POLLINIGNEOF;
 
 	if ((events & POLLINIGNEOF) == 0) {
diff --git a/sys/sys/pipe.h b/sys/sys/pipe.h
index 36e3021..d60185a 100644
--- a/sys/sys/pipe.h
+++ b/sys/sys/pipe.h
@@ -96,6 +96,7 @@ struct pipemapping {
 #define PIPE_DIRECTW	0x400	/* Pipe direct write active. */
 #define PIPE_DIRECTOK	0x800	/* Direct mode ok. */
 #define PIPE_NAMED	0x1000	/* Is a named pipe. */
+#define PIPE_SAMEWGEN	0x2000	/* same write generation for named pipes. */
 
 /*
  * Per-pipe data structure.