From f950879e16c0a4c794beff0731a53494613e9c56 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Wed, 7 Mar 2012 07:31:50 +0000
Subject: 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)
---
 sys/fs/fifofs/fifo.h       |  1 -
 sys/fs/fifofs/fifo_vnops.c | 25 ++++++++++++-------------
 2 files changed, 12 insertions(+), 14 deletions(-)

(limited to 'sys/fs')

diff --git a/sys/fs/fifofs/fifo.h b/sys/fs/fifofs/fifo.h
index 94bccc68466a..da85ae23d86b 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 1cc17cf9e6fd..65c44ae2cab8 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);
-}
-
-- 
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