Module Name: src
Committed By: ad
Date: Fri Apr 10 17:18:04 UTC 2020
Modified Files:
src/sys/kern: vfs_bio.c
src/sys/sys: buf.h
Log Message:
Remove buffer reference counting, now that it's safe to destroy b_busy after
waking any waiters.
To generate a diff of this commit:
cvs rdiff -u -r1.290 -r1.291 src/sys/kern/vfs_bio.c
cvs rdiff -u -r1.131 -r1.132 src/sys/sys/buf.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/vfs_bio.c
diff -u src/sys/kern/vfs_bio.c:1.290 src/sys/kern/vfs_bio.c:1.291
--- src/sys/kern/vfs_bio.c:1.290 Sat Mar 14 18:08:39 2020
+++ src/sys/kern/vfs_bio.c Fri Apr 10 17:18:04 2020
@@ -1,7 +1,7 @@
-/* $NetBSD: vfs_bio.c,v 1.290 2020/03/14 18:08:39 ad Exp $ */
+/* $NetBSD: vfs_bio.c,v 1.291 2020/04/10 17:18:04 ad Exp $ */
/*-
- * Copyright (c) 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
+ * Copyright (c) 2007, 2008, 2009, 2019, 2020 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
@@ -123,7 +123,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.290 2020/03/14 18:08:39 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.291 2020/04/10 17:18:04 ad Exp $");
#ifdef _KERNEL_OPT
#include "opt_bufcache.h"
@@ -228,8 +228,6 @@ static int checkfreelist(buf_t *, struct
#endif
static void biointr(void *);
static void biodone2(buf_t *);
-static void bref(buf_t *);
-static void brele(buf_t *);
static void sysctl_kern_buf_setup(void);
static void sysctl_vm_buf_setup(void);
@@ -411,38 +409,6 @@ bremfree(buf_t *bp)
}
/*
- * Add a reference to an buffer structure that came from buf_cache.
- */
-static inline void
-bref(buf_t *bp)
-{
-
- KASSERT(mutex_owned(&bufcache_lock));
- KASSERT(bp->b_refcnt > 0);
-
- bp->b_refcnt++;
-}
-
-/*
- * Free an unused buffer structure that came from buf_cache.
- */
-static inline void
-brele(buf_t *bp)
-{
-
- KASSERT(mutex_owned(&bufcache_lock));
- KASSERT(bp->b_refcnt > 0);
-
- if (bp->b_refcnt-- == 1) {
- buf_destroy(bp);
-#ifdef DEBUG
- memset((char *)bp, 0, sizeof(*bp));
-#endif
- pool_cache_put(buf_cache, bp);
- }
-}
-
-/*
* note that for some ports this is used by pmap bootstrap code to
* determine kva size.
*/
@@ -1054,7 +1020,6 @@ brelsel(buf_t *bp, int set)
KASSERT(bp != NULL);
KASSERT(mutex_owned(&bufcache_lock));
KASSERT(!cv_has_waiters(&bp->b_done));
- KASSERT(bp->b_refcnt > 0);
SET(bp->b_cflags, set);
@@ -1175,14 +1140,19 @@ already_queued:
* prevent a thundering herd: many LWPs simultaneously awakening and
* competing for the buffer's lock. Testing in 2019 revealed this
* to reduce contention on bufcache_lock tenfold during a kernel
- * compile. Elsewhere, when the buffer is changing identity, being
- * disposed of, or moving from one list to another, we wake all lock
- * requestors.
+ * compile. Here and elsewhere, when the buffer is changing
+ * identity, being disposed of, or moving from one list to another,
+ * we wake all lock requestors.
*/
- cv_signal(&bp->b_busy);
-
- if (bp->b_bufsize <= 0)
- brele(bp);
+ if (bp->b_bufsize <= 0) {
+ cv_broadcast(&bp->b_busy);
+ buf_destroy(bp);
+#ifdef DEBUG
+ memset((char *)bp, 0, sizeof(*bp));
+#endif
+ pool_cache_put(buf_cache, bp);
+ } else
+ cv_signal(&bp->b_busy);
}
void
@@ -1494,7 +1464,6 @@ getnewbuf(int slpflag, int slptimeo, int
}
KASSERT(ISSET(bp->b_cflags, BC_BUSY));
- KASSERT(bp->b_refcnt > 0);
KASSERT(!cv_has_waiters(&bp->b_done));
/*
@@ -1603,7 +1572,6 @@ biowait(buf_t *bp)
BIOHIST_FUNC(__func__);
KASSERT(ISSET(bp->b_cflags, BC_BUSY));
- KASSERT(bp->b_refcnt > 0);
SDT_PROBE1(io, kernel, , wait__start, bp);
@@ -2172,7 +2140,6 @@ buf_init(buf_t *bp)
bp->b_oflags = 0;
bp->b_objlock = &buffer_lock;
bp->b_iodone = NULL;
- bp->b_refcnt = 1;
bp->b_dev = NODEV;
bp->b_vnbufs.le_next = NOLIST;
BIO_SETPRIO(bp, BPRIO_DEFAULT);
@@ -2201,7 +2168,6 @@ bbusy(buf_t *bp, bool intr, int timo, km
goto out;
}
bp->b_cflags |= BC_WANTED;
- bref(bp);
if (interlock != NULL)
mutex_exit(interlock);
if (intr) {
@@ -2211,16 +2177,18 @@ bbusy(buf_t *bp, bool intr, int timo, km
error = cv_timedwait(&bp->b_busy, &bufcache_lock,
timo);
}
- brele(bp);
+ /*
+ * At this point the buffer may be gone: don't touch it
+ * again. The caller needs to find it again and retry.
+ */
if (interlock != NULL)
mutex_enter(interlock);
- if (error != 0)
- goto out;
- error = EPASSTHROUGH;
- goto out;
+ if (error == 0)
+ error = EPASSTHROUGH;
+ } else {
+ bp->b_cflags |= BC_BUSY;
+ error = 0;
}
- bp->b_cflags |= BC_BUSY;
- error = 0;
out: SDT_PROBE5(io, kernel, , bbusy__done,
bp, intr, timo, interlock, error);
Index: src/sys/sys/buf.h
diff -u src/sys/sys/buf.h:1.131 src/sys/sys/buf.h:1.132
--- src/sys/sys/buf.h:1.131 Mon Aug 26 10:24:39 2019
+++ src/sys/sys/buf.h Fri Apr 10 17:18:04 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: buf.h,v 1.131 2019/08/26 10:24:39 msaitoh Exp $ */
+/* $NetBSD: buf.h,v 1.132 2020/04/10 17:18:04 ad Exp $ */
/*-
* Copyright (c) 1999, 2000, 2007, 2008 The NetBSD Foundation, Inc.
@@ -149,7 +149,6 @@ struct buf {
off_t b_dcookie; /* NFS: Offset cookie if dir block */
kcondvar_t b_busy; /* c: threads waiting on buf */
- u_int b_refcnt; /* c: refcount for b_busy */
void *b_unused; /* : unused */
LIST_ENTRY(buf) b_hash; /* c: hash chain */
LIST_ENTRY(buf) b_vnbufs; /* c: associated vnode */
