When filt_proc() removes event from the knlist due to the process

exiting (NOTE_EXIT->knlist_remove_inevent()), two things happen:
- knote kn_knlist pointer is reset
- INFLUX knote is removed from the process knlist.
And, there are two consequences:
- KN_LIST_UNLOCK() on such knote is nop
- there is nothing which would block exit1() from processing past the
  knlist_destroy() (and knlist_destroy() resets knlist lock pointers).
Both consequences result either in leaked process lock, or
dereferencing NULL function pointers for locking.

Handle this by stopping embedding the process knlist into struct proc.
Instead, the knlist is allocated together with struct proc, but marked
as autodestroy on the zombie reap, by knlist_detach() function.  The
knlist is freed when last kevent is removed from the list, in
particular, at the zombie reap time if the list is empty.  As result,
the knlist_remove_inevent() is no longer needed and removed.

Other changes:

In filt_procattach(), clear NOTE_EXEC and NOTE_FORK desired events
from kn_sfflags for knote registered by kernel to only get NOTE_CHILD
notifications.  The flags leak resulted in excessive
NOTE_EXEC/NOTE_FORK reports.

Fix immediate note activation in filt_procattach().  Condition should
be either the immediate CHILD_NOTE activation, or immediate NOTE_EXIT
report for the exiting process.

In knote_fork(), do not perform racy check for KN_INFLUX before kq
lock is taken.  Besides being racy, it did not accounted for notes
just added by scan (KN_SCAN).

Some minor and incomplete style fixes.

Analyzed and tested by:	Eric Badger <eric@badgerio.us>
Reviewed by:	jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Approved by:	re (gjb)
Differential revision:	https://reviews.freebsd.org/D6859

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 035a704c72fb..b46cb722ce4f 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -748,7 +748,7 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
 	/*
 	 * Tell any interested parties about the new process.
 	 */
-	knote_fork(&p1->p_klist, p2->p_pid);
+	knote_fork(p1->p_klist, p2->p_pid);
 	SDT_PROBE3(proc, , , create, p2, p1, fr->fr_flags);
 
 	if (fr->fr_flags & RFPROCDESC) {
@@ -950,7 +950,7 @@ fork1(struct thread *td, struct fork_req *fr)
 #ifdef MAC
 	mac_proc_init(newproc);
 #endif
-	knlist_init_mtx(&newproc->p_klist, &newproc->p_mtx);
+	newproc->p_klist = knlist_alloc(&newproc->p_mtx);
 	STAILQ_INIT(&newproc->p_ktr);
 
 	/* We have to lock the process tree while we look for a pid. */