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	Index: share/man/man4/filemon.4
	===================================================================
	--- share/man/man4/filemon.4
	+++ share/man/man4/filemon.4
	@@ -31,7 +31,7 @@
	.\"
	.\" $FreeBSD$
	.\"
	-.Dd January 28, 2016
	+.Dd March 7, 2016
	.Dt FILEMON 4
	.Os
	.Sh NAME
	@@ -186,14 +186,5 @@
	device appeared in
	.Fx 9.1 .
	.Sh BUGS
	-Loading
	-.Nm
	-may reduce system performance for the noted syscalls.
	-.Pp
	-Only children of the set process are logged.
	-Processes can escape being traced by double forking.
	-This is not seen as a problem as the intended use is build monitoring, which
	-does not make sense to have daemons for.
	-.Pp
	Unloading the module may panic the system, thus requires using
	.Ic kldunload -f .
	Index: sys/dev/filemon/filemon.c
	===================================================================
	--- sys/dev/filemon/filemon.c
	+++ sys/dev/filemon/filemon.c
	@@ -46,7 +46,6 @@
	#include <sys/module.h>
	#include <sys/poll.h>
	#include <sys/proc.h>
	-#include <sys/queue.h>
	#include <sys/sx.h>
	#include <sys/syscall.h>
	#include <sys/sysent.h>
	@@ -80,23 +79,113 @@
	MALLOC_DECLARE(M_FILEMON);
	MALLOC_DEFINE(M_FILEMON, "filemon", "File access monitor");

	+/*
	+ * The filemon->lock protects several things currently:
	+ * - fname1/fname2/msgbufr are pre-allocated and used per syscall
	+ * for logging and copyins rather than stack variables.
	+ * - Serializing the filemon's log output.
	+ * - Preventing inheritance or removal of the filemon into proc.p_filemon.
	+ */
	struct filemon {
	- TAILQ_ENTRY(filemon) link; /* Link into the in-use list. */
	- struct sx lock; /* Lock mutex for this filemon. */
	+ struct sx lock; /* Lock for this filemon. */
	struct file fp; / Output file pointer. */
	- struct proc p; / The process being monitored. */
	char fname1[MAXPATHLEN]; /* Temporary filename buffer. */
	char fname2[MAXPATHLEN]; /* Temporary filename buffer. */
	char msgbufr[1024]; /* Output message buffer. */
	+ volatile u_int refcnt; /* Pointer reference count. */
	};

	-static TAILQ_HEAD(, filemon) filemons_inuse = TAILQ_HEAD_INITIALIZER(filemons_inuse);
	-static TAILQ_HEAD(, filemon) filemons_free = TAILQ_HEAD_INITIALIZER(filemons_free);
	-static struct sx access_lock;
	-
	static struct cdev *filemon_dev;
	+static void filemon_output(struct filemon filemon, char msg, size_t len);
	+
	+static __inline struct filemon *
	+filemon_acquire(struct filemon *filemon)
	+{
	+
	+ if (filemon != NULL)
	+ refcount_acquire(&filemon->refcnt);
	+ return (filemon);
	+}
	+
	+/*
	+ * Release a reference and on the last one write the footer and free the
	+ * filemon.
	+ */
	+static void
	+filemon_release(struct filemon *filemon)
	+{
	+ size_t len;
	+ struct timeval now;
	+
	+ if (refcount_release(&filemon->refcnt) == 0)
	+ return;
	+
	+ sx_assert(&filemon->lock, SA_UNLOCKED);
	+
	+ if (filemon->fp != NULL) {
	+ getmicrotime(&now);
	+
	+ len = snprintf(filemon->msgbufr,
	+ sizeof(filemon->msgbufr),
	+ "# Stop %ju.%06ju\n# Bye bye\n",
	+ (uintmax_t)now.tv_sec, (uintmax_t)now.tv_usec);
	+
	+ filemon_output(filemon, filemon->msgbufr, len);
	+ fdrop(filemon->fp, curthread);
	+ }
	+
	+ sx_destroy(&filemon->lock);
	+ free(filemon, M_FILEMON);
	+}
	+
	+/*
	+ * Acquire the proc's p_filemon reference and lock the filemon.
	+ * The proc's p_filemon may not match this filemon on return.
	+ */
	+static struct filemon *
	+filemon_proc_get(struct proc *p)
	+{
	+ struct filemon *filemon;
	+
	+ PROC_LOCK(p);
	+ filemon = filemon_acquire(p->p_filemon);
	+ PROC_UNLOCK(p);
	+
	+ if (filemon == NULL)
	+ return (NULL);
	+ /*
	+ * The p->p_filemon may have changed by now. That case is handled
	+ * by the exit and fork hooks and filemon_attach_proc specially.
	+ */
	+ sx_xlock(&filemon->lock);
	+ return (filemon);
	+}
	+
	+/* Remove and release the filemon on the given process. */
	+static void
	+filemon_proc_drop(struct proc *p)
	+{
	+ struct filemon *filemon;
	+
	+ KASSERT(p->p_filemon != NULL, ("%s: proc %p NULL p_filemon",
	+ __func__, p));
	+ sx_assert(&p->p_filemon->lock, SA_XLOCKED);
	+ PROC_LOCK(p);
	+ filemon = p->p_filemon;
	+ p->p_filemon = NULL;
	+ PROC_UNLOCK(p);
	+ filemon_release(filemon);
	+}
	+
	+/* Unlock and release the filemon. */
	+static __inline void
	+filemon_drop(struct filemon *filemon)
	+{
	+
	+ sx_xunlock(&filemon->lock);
	+ filemon_release(filemon);
	+}

	-#include "filemon_lock.c"
	#include "filemon_wrapper.c"

	static void
	@@ -115,35 +204,118 @@
	filemon_output(filemon, filemon->msgbufr, len);
	}

	+/*
	+ * Invalidate the passed filemon in all processes.
	+ */
	static void
	-filemon_dtr(void *data)
	+filemon_untrack_processes(struct filemon *filemon)
	{
	- struct filemon *filemon = data;
	+ struct proc *p;

	- if (filemon != NULL) {
	- struct file *fp;
	+ sx_assert(&filemon->lock, SA_XLOCKED);

	- /* Follow same locking order as filemon_pid_check. */
	- filemon_lock_write();
	- sx_xlock(&filemon->lock);
	+ /* First reference is in the cdevpriv. */
	+ if (filemon->refcnt == 1)
	+ return;

	- /* Remove from the in-use list. */
	- TAILQ_REMOVE(&filemons_inuse, filemon, link);
	+ /*
	+ * Processes in this list won't go away while here since
	+ * filemon_event_process_exit() will lock on filemon->lock
	+ * which we hold.
	+ */
	+ sx_slock(&allproc_lock);
	+ FOREACH_PROC_IN_SYSTEM(p) {
	+ /*
	+ * No PROC_LOCK is needed to compare here since it is
	+ * guaranteed to not change since we have its filemon
	+ * locked. Everything that changes this p_filemon will
	+ * be locked on it.
	+ */
	+ if (p->p_filemon == filemon)
	+ filemon_proc_drop(p);
	+ }
	+ sx_sunlock(&allproc_lock);

	- fp = filemon->fp;
	- filemon->fp = NULL;
	- filemon->p = NULL;
	+ /*
	+ * It's possible some references were acquired but will be
	+ * dropped shortly as they are restricted from being
	+ * inherited.
	+ */
	+}

	- /* Add to the free list. */
	- TAILQ_INSERT_TAIL(&filemons_free, filemon, link);
	+/* The devfs file is being closed. Untrace all processes. */
	+static void
	+filemon_dtr(void *data)
	+{
	+ struct filemon *filemon = data;
	+
	+ if (filemon == NULL)
	+ return;

	- /* Give up write access. */
	- sx_xunlock(&filemon->lock);
	- filemon_unlock_write();
	+ sx_xlock(&filemon->lock);
	+ /*
	+ * Detach the filemon. The actual closing of it may not
	+ * occur until syscalls in other threads with references complete.
	+ * The filemon cannot be inherited after this though.
	+ */
	+ filemon_untrack_processes(filemon);
	+ filemon_drop(filemon);
	+}

	- if (fp != NULL)
	- fdrop(fp, curthread);
	+/* Attach the filemon to the process. */
	+static int
	+filemon_attach_proc(struct filemon filemon, struct proc p)
	+{
	+ struct filemon *filemon2;
	+
	+ sx_assert(&filemon->lock, SA_XLOCKED);
	+ PROC_LOCK_ASSERT(p, MA_OWNED);
	+ KASSERT((p->p_flag & P_WEXIT) == 0,
	+ ("%s: filemon %p attaching to exiting process %p",
	+ __func__, filemon, p));
	+
	+ if (p->p_filemon == filemon)
	+ return (0);
	+
	+ /*
	+ * Historic behavior of filemon has been to let a child initiate
	+ * tracing on itself and cease tracing in the parent. Bmake
	+ * .META + .MAKE relies on this. It is only relevant for attaching to
	+ * curproc.
	+ */
	+ if (p->p_filemon != NULL) {
	+ /*
	+ * Don't allow truncating other process traces. It is
	+ * not really intended to trace procs other than curproc
	+ * anyhow.
	+ */
	+ if (p != curproc)
	+ return (EBUSY);
	+
	+ do {
	+ PROC_UNLOCK(p);
	+ sx_xunlock(&filemon->lock);
	+ while ((filemon2 = filemon_proc_get(p)) != NULL) {
	+ /* It may have changed. */
	+ if (p->p_filemon == filemon2)
	+ filemon_proc_drop(p);
	+ filemon_drop(filemon2);
	+ }
	+ sx_xlock(&filemon->lock);
	+ PROC_LOCK(p);
	+ /*
	+ * It may have been attached to, though unlikely.
	+ * Try again if needed.
	+ */
	+ } while (p->p_filemon != NULL);
	+ KASSERT(p->p_filemon == NULL,
	+ ("%s: proc %p didn't detach filemon %p", __func__, p,
	+ p->p_filemon));
	}
	+
	+ p->p_filemon = filemon_acquire(filemon);
	+
	+ return (0);
	}

	static int
	@@ -176,10 +348,16 @@

	/* Set the monitored process ID. */
	case FILEMON_SET_PID:
	+ /* Invalidate any existing processes already set. */
	+ filemon_untrack_processes(filemon);
	+
	error = pget(((pid_t )data), PGET_CANDEBUG \| PGET_NOTWEXIT,
	&p);
	if (error == 0) {
	- filemon->p = p;
	+ KASSERT(p->p_filemon != filemon,
	+ ("%s: proc %p didn't untrack filemon %p",
	+ __func__, p, filemon));
	+ error = filemon_attach_proc(filemon, p);
	PROC_UNLOCK(p);
	}
	break;
	@@ -197,35 +375,19 @@
	filemon_open(struct cdev *dev, int oflags __unused, int devtype __unused,
	struct thread *td __unused)
	{
	+ int error;
	struct filemon *filemon;

	- /* Get exclusive write access. */
	- filemon_lock_write();
	+ filemon = malloc(sizeof(*filemon), M_FILEMON,
	+ M_WAITOK \| M_ZERO);
	+ sx_init(&filemon->lock, "filemon");
	+ refcount_init(&filemon->refcnt, 1);

	- if ((filemon = TAILQ_FIRST(&filemons_free)) != NULL)
	- TAILQ_REMOVE(&filemons_free, filemon, link);
	+ error = devfs_set_cdevpriv(filemon, filemon_dtr);
	+ if (error != 0)
	+ filemon_release(filemon);

	- /* Give up write access. */
	- filemon_unlock_write();
	-
	- if (filemon == NULL) {
	- filemon = malloc(sizeof(struct filemon), M_FILEMON,
	- M_WAITOK \| M_ZERO);
	- sx_init(&filemon->lock, "filemon");
	- }
	-
	- devfs_set_cdevpriv(filemon, filemon_dtr);
	-
	- /* Get exclusive write access. */
	- filemon_lock_write();
	-
	- /* Add to the in-use list. */
	- TAILQ_INSERT_TAIL(&filemons_inuse, filemon, link);
	-
	- /* Give up write access. */
	- filemon_unlock_write();
	-
	- return (0);
	+ return (error);
	}

	static int
	@@ -239,7 +401,6 @@
	static void
	filemon_load(void *dummy __unused)
	{
	- sx_init(&access_lock, "filemons_inuse");

	/* Install the syscall wrappers. */
	filemon_wrapper_install();
	@@ -251,38 +412,11 @@
	static int
	filemon_unload(void)
	{
	- struct filemon *filemon;
	- int error = 0;

	- /* Get exclusive write access. */
	- filemon_lock_write();
	+ destroy_dev(filemon_dev);
	+ filemon_wrapper_deinstall();

	- if (TAILQ_FIRST(&filemons_inuse) != NULL)
	- error = EBUSY;
	- else {
	- destroy_dev(filemon_dev);
	-
	- /* Deinstall the syscall wrappers. */
	- filemon_wrapper_deinstall();
	- }
	-
	- /* Give up write access. */
	- filemon_unlock_write();
	-
	- if (error == 0) {
	- /* free() filemon structs free list. */
	- filemon_lock_write();
	- while ((filemon = TAILQ_FIRST(&filemons_free)) != NULL) {
	- TAILQ_REMOVE(&filemons_free, filemon, link);
	- sx_destroy(&filemon->lock);
	- free(filemon, M_FILEMON);
	- }
	- filemon_unlock_write();
	-
	- sx_destroy(&access_lock);
	- }
	-
	- return (error);
	+ return (0);
	}

	static int
	Index: sys/dev/filemon/filemon_lock.c
	===================================================================
	--- sys/dev/filemon/filemon_lock.c
	+++ /dev/null
	@@ -1,57 +0,0 @@
	-/*-
	- * Copyright (c) 2009-2011, Juniper Networks, Inc.
	- * Copyright (c) 2015, EMC Corp.
	- * All rights reserved.
	- *
	- * Redistribution and use in source and binary forms, with or without
	- * modification, are permitted provided that the following conditions
	- * are met:
	- * 1. Redistributions of source code must retain the above copyright
	- * notice, this list of conditions and the following disclaimer.
	- * 2. Redistributions in binary form must reproduce the above copyright
	- * notice, this list of conditions and the following disclaimer in the
	- * documentation and/or other materials provided with the distribution.
	- *
	- * THIS SOFTWARE IS PROVIDED BY JUNIPER NETWORKS AND CONTRIBUTORS ``AS IS'' AND
	- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	- * ARE DISCLAIMED. IN NO EVENT SHALL JUNIPER NETWORKS OR CONTRIBUTORS BE LIABLE
	- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	- * SUCH DAMAGE.
	- */
	-
	-#include <sys/cdefs.h>
	-__FBSDID("$FreeBSD$");
	-
	-static __inline void
	-filemon_lock_read(void)
	-{
	-
	- sx_slock(&access_lock);
	-}
	-
	-static __inline void
	-filemon_unlock_read(void)
	-{
	-
	- sx_sunlock(&access_lock);
	-}
	-
	-static __inline void
	-filemon_lock_write(void)
	-{
	-
	- sx_xlock(&access_lock);
	-}
	-
	-static __inline void
	-filemon_unlock_write(void)
	-{
	-
	- sx_xunlock(&access_lock);
	-}
	Index: sys/dev/filemon/filemon_wrapper.c
	===================================================================
	--- sys/dev/filemon/filemon_wrapper.c
	+++ sys/dev/filemon/filemon_wrapper.c
	@@ -65,33 +65,6 @@
	fo_write(filemon->fp, &auio, curthread->td_ucred, 0, curthread);
	}

	-static struct filemon *
	-filemon_pid_check(struct proc *p)
	-{
	- struct filemon *filemon;
	-
	- filemon_lock_read();
	- if (TAILQ_EMPTY(&filemons_inuse)) {
	- filemon_unlock_read();
	- return (NULL);
	- }
	- sx_slock(&proctree_lock);
	- while (p->p_pid != 0) {
	- TAILQ_FOREACH(filemon, &filemons_inuse, link) {
	- if (p == filemon->p) {
	- sx_sunlock(&proctree_lock);
	- sx_xlock(&filemon->lock);
	- filemon_unlock_read();
	- return (filemon);
	- }
	- }
	- p = proc_realparent(p);
	- }
	- sx_sunlock(&proctree_lock);
	- filemon_unlock_read();
	- return (NULL);
	-}
	-
	static int
	filemon_wrapper_chdir(struct thread td, struct chdir_args uap)
	{
	@@ -101,7 +74,7 @@
	struct filemon *filemon;

	if ((ret = sys_chdir(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -111,7 +84,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -126,7 +99,7 @@
	char fullpath, freepath;
	size_t len;

	- if ((filemon = filemon_pid_check(p)) != NULL) {
	+ if ((filemon = filemon_proc_get(p)) != NULL) {
	fullpath = "<unknown>";
	freepath = NULL;

	@@ -139,7 +112,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);

	free(freepath, M_TEMP);
	}
	@@ -154,7 +127,7 @@
	struct filemon *filemon;

	if ((ret = sys_open(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -177,7 +150,7 @@
	curproc->p_pid, filemon->fname1);
	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -193,7 +166,7 @@
	struct filemon *filemon;

	if ((ret = sys_openat(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -229,7 +202,7 @@
	curproc->p_pid, filemon->fname2, filemon->fname1);
	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -245,7 +218,7 @@
	struct filemon *filemon;

	if ((ret = sys_rename(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->from, filemon->fname1,
	sizeof(filemon->fname1), &done);
	copyinstr(uap->to, filemon->fname2,
	@@ -257,7 +230,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -273,7 +246,7 @@
	struct filemon *filemon;

	if ((ret = sys_link(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);
	copyinstr(uap->link, filemon->fname2,
	@@ -285,7 +258,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -301,7 +274,7 @@
	struct filemon *filemon;

	if ((ret = sys_symlink(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);
	copyinstr(uap->link, filemon->fname2,
	@@ -313,7 +286,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -329,7 +302,7 @@
	struct filemon *filemon;

	if ((ret = sys_linkat(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path1, filemon->fname1,
	sizeof(filemon->fname1), &done);
	copyinstr(uap->path2, filemon->fname2,
	@@ -341,7 +314,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -357,7 +330,7 @@
	struct filemon *filemon;

	if ((ret = sys_stat(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -367,7 +340,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -385,7 +358,7 @@
	struct filemon *filemon;

	if ((ret = freebsd32_stat(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -395,7 +368,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -408,29 +381,22 @@
	{
	size_t len;
	struct filemon *filemon;
	- struct timeval now;
	-
	- /* Get timestamp before locking. */
	- getmicrotime(&now);

	- if ((filemon = filemon_pid_check(p)) != NULL) {
	+ if ((filemon = filemon_proc_get(p)) != NULL) {
	len = snprintf(filemon->msgbufr, sizeof(filemon->msgbufr),
	"X %d %d %d\n", p->p_pid, p->p_xexit, p->p_xsig);

	filemon_output(filemon, filemon->msgbufr, len);

	- /* Check if the monitored process is about to exit. */
	- if (filemon->p == p) {
	- len = snprintf(filemon->msgbufr,
	- sizeof(filemon->msgbufr),
	- "# Stop %ju.%06ju\n# Bye bye\n",
	- (uintmax_t)now.tv_sec, (uintmax_t)now.tv_usec);
	-
	- filemon_output(filemon, filemon->msgbufr, len);
	- filemon->p = NULL;
	- }
	+ /*
	+ * filemon_untrack_processes() may have dropped this p_filemon
	+ * already while in filemon_proc_get() before acquiring the
	+ * filemon lock.
	+ */
	+ if (p->p_filemon == filemon)
	+ filemon_proc_drop(p);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -443,7 +409,7 @@
	struct filemon *filemon;

	if ((ret = sys_unlink(td, uap)) == 0) {
	- if ((filemon = filemon_pid_check(curproc)) != NULL) {
	+ if ((filemon = filemon_proc_get(curproc)) != NULL) {
	copyinstr(uap->path, filemon->fname1,
	sizeof(filemon->fname1), &done);

	@@ -453,7 +419,7 @@

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ filemon_drop(filemon);
	}
	}

	@@ -467,14 +433,32 @@
	size_t len;
	struct filemon *filemon;

	- if ((filemon = filemon_pid_check(p1)) != NULL) {
	+ if ((filemon = filemon_proc_get(p1)) != NULL) {
	len = snprintf(filemon->msgbufr,
	sizeof(filemon->msgbufr), "F %d %d\n",
	p1->p_pid, p2->p_pid);

	filemon_output(filemon, filemon->msgbufr, len);

	- sx_xunlock(&filemon->lock);
	+ /*
	+ * filemon_untrack_processes() or
	+ * filemon_ioctl(FILEMON_SET_PID) may have changed the parent's
	+ * p_filemon while in filemon_proc_get() before acquiring the
	+ * filemon lock. Only inherit if the parent is still traced by
	+ * this filemon.
	+ */
	+ if (p1->p_filemon == filemon) {
	+ PROC_LOCK(p2);
	+ /*
	+ * It may have been attached to already by a new
	+ * filemon.
	+ */
	+ if (p2->p_filemon == NULL)
	+ p2->p_filemon = filemon_acquire(filemon);
	+ PROC_UNLOCK(p2);
	+ }
	+
	+ filemon_drop(filemon);
	}
	}

	Index: sys/sys/proc.h
	===================================================================
	--- sys/sys/proc.h
	+++ sys/sys/proc.h
	@@ -162,6 +162,7 @@
	*/
	struct cpuset;
	struct filecaps;
	+struct filemon;
	struct kaioinfo;
	struct kaudit_record;
	struct kdtrace_proc;
	@@ -580,6 +581,7 @@
	struct procdesc p_procdesc; / (e) Process descriptor, if any. */
	u_int p_treeflag; /* (e) P_TREE flags */
	int p_pendingexits; /* (c) Count of pending thread exits. */
	+ struct filemon p_filemon; / (c) filemon-specific data. */
	/* End area that is zeroed on creation. */
	#define p_endzero p_magic

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