Remove buffer reference counting, now that it's safe to destroy b_busy after
waking any waiters.
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parent
e0bb7e8edd
commit
83f44bb607
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@ -1,7 +1,7 @@
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/* $NetBSD: vfs_bio.c,v 1.290 2020/03/14 18:08:39 ad Exp $ */
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/* $NetBSD: vfs_bio.c,v 1.291 2020/04/10 17:18:04 ad Exp $ */
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/*-
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* Copyright (c) 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
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* Copyright (c) 2007, 2008, 2009, 2019, 2020 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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@ -123,7 +123,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.290 2020/03/14 18:08:39 ad Exp $");
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__KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v 1.291 2020/04/10 17:18:04 ad Exp $");
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#ifdef _KERNEL_OPT
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#include "opt_bufcache.h"
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@ -228,8 +228,6 @@ static int checkfreelist(buf_t *, struct bqueue *, int);
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#endif
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static void biointr(void *);
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static void biodone2(buf_t *);
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static void bref(buf_t *);
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static void brele(buf_t *);
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static void sysctl_kern_buf_setup(void);
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static void sysctl_vm_buf_setup(void);
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@ -410,38 +408,6 @@ bremfree(buf_t *bp)
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#endif /* defined(DIAGNOSTIC) */
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}
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/*
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* Add a reference to an buffer structure that came from buf_cache.
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*/
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static inline void
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bref(buf_t *bp)
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{
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KASSERT(mutex_owned(&bufcache_lock));
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KASSERT(bp->b_refcnt > 0);
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bp->b_refcnt++;
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}
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/*
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* Free an unused buffer structure that came from buf_cache.
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*/
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static inline void
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brele(buf_t *bp)
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{
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KASSERT(mutex_owned(&bufcache_lock));
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KASSERT(bp->b_refcnt > 0);
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if (bp->b_refcnt-- == 1) {
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buf_destroy(bp);
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#ifdef DEBUG
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memset((char *)bp, 0, sizeof(*bp));
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#endif
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pool_cache_put(buf_cache, bp);
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}
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}
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/*
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* note that for some ports this is used by pmap bootstrap code to
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* determine kva size.
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@ -1054,7 +1020,6 @@ brelsel(buf_t *bp, int set)
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KASSERT(bp != NULL);
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KASSERT(mutex_owned(&bufcache_lock));
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KASSERT(!cv_has_waiters(&bp->b_done));
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KASSERT(bp->b_refcnt > 0);
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SET(bp->b_cflags, set);
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@ -1175,14 +1140,19 @@ already_queued:
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* prevent a thundering herd: many LWPs simultaneously awakening and
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* competing for the buffer's lock. Testing in 2019 revealed this
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* to reduce contention on bufcache_lock tenfold during a kernel
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* compile. Elsewhere, when the buffer is changing identity, being
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* disposed of, or moving from one list to another, we wake all lock
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* requestors.
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* compile. Here and elsewhere, when the buffer is changing
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* identity, being disposed of, or moving from one list to another,
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* we wake all lock requestors.
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*/
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if (bp->b_bufsize <= 0) {
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cv_broadcast(&bp->b_busy);
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buf_destroy(bp);
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#ifdef DEBUG
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memset((char *)bp, 0, sizeof(*bp));
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#endif
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pool_cache_put(buf_cache, bp);
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} else
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cv_signal(&bp->b_busy);
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if (bp->b_bufsize <= 0)
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brele(bp);
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}
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void
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@ -1494,7 +1464,6 @@ getnewbuf(int slpflag, int slptimeo, int from_bufq)
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}
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KASSERT(ISSET(bp->b_cflags, BC_BUSY));
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KASSERT(bp->b_refcnt > 0);
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KASSERT(!cv_has_waiters(&bp->b_done));
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/*
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@ -1603,7 +1572,6 @@ biowait(buf_t *bp)
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BIOHIST_FUNC(__func__);
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KASSERT(ISSET(bp->b_cflags, BC_BUSY));
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KASSERT(bp->b_refcnt > 0);
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SDT_PROBE1(io, kernel, , wait__start, bp);
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@ -2172,7 +2140,6 @@ buf_init(buf_t *bp)
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bp->b_oflags = 0;
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bp->b_objlock = &buffer_lock;
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bp->b_iodone = NULL;
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bp->b_refcnt = 1;
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bp->b_dev = NODEV;
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bp->b_vnbufs.le_next = NOLIST;
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BIO_SETPRIO(bp, BPRIO_DEFAULT);
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@ -2201,7 +2168,6 @@ bbusy(buf_t *bp, bool intr, int timo, kmutex_t *interlock)
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goto out;
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}
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bp->b_cflags |= BC_WANTED;
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bref(bp);
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if (interlock != NULL)
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mutex_exit(interlock);
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if (intr) {
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@ -2211,16 +2177,18 @@ bbusy(buf_t *bp, bool intr, int timo, kmutex_t *interlock)
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error = cv_timedwait(&bp->b_busy, &bufcache_lock,
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timo);
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}
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brele(bp);
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/*
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* At this point the buffer may be gone: don't touch it
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* again. The caller needs to find it again and retry.
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*/
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if (interlock != NULL)
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mutex_enter(interlock);
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if (error != 0)
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goto out;
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if (error == 0)
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error = EPASSTHROUGH;
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goto out;
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}
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} else {
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bp->b_cflags |= BC_BUSY;
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error = 0;
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}
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out: SDT_PROBE5(io, kernel, , bbusy__done,
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bp, intr, timo, interlock, error);
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@ -1,4 +1,4 @@
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/* $NetBSD: buf.h,v 1.131 2019/08/26 10:24:39 msaitoh Exp $ */
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/* $NetBSD: buf.h,v 1.132 2020/04/10 17:18:04 ad Exp $ */
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/*-
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* Copyright (c) 1999, 2000, 2007, 2008 The NetBSD Foundation, Inc.
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@ -149,7 +149,6 @@ struct buf {
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off_t b_dcookie; /* NFS: Offset cookie if dir block */
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kcondvar_t b_busy; /* c: threads waiting on buf */
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u_int b_refcnt; /* c: refcount for b_busy */
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void *b_unused; /* : unused */
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LIST_ENTRY(buf) b_hash; /* c: hash chain */
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LIST_ENTRY(buf) b_vnbufs; /* c: associated vnode */
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