git: 8394a99386fe - stable/13 - setitimer: Fix exit race

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=8394a99386fe5ff98b50fedde480ec35fb397717

commit 8394a99386fe5ff98b50fedde480ec35fb397717
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2022-03-23 16:36:12 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2022-04-22 14:35:42 +0000

    setitimer: Fix exit race
    
    We use the p_itcallout callout, interlocked by the proc lock, to
    schedule timeouts for the setitimer(2) system call.  When a process
    exits, the callout must be stopped before the process struct is
    recycled.
    
    Currently we attempt to stop the callout in exit1() with the call
    _callout_stop_safe(&p->p_itcallout, CS_EXECUTING).  If this call returns
    0, then we sleep in order to drain the callout.  However, this happens
    only if the callout is not scheduled at all.  If the callout thread is
    blocked on the proc lock, then exit1() will not block and the callout
    may execute after the process has fully exited, typically resulting in a
    panic.
    
    I cannot see a reason to use the CS_EXECUTING flag here.  Instead, use
    the regular callout_stop()/callout_drain() dance to halt the callout.
    
    Reported by:    ler
    Tested by:      ler, pho
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit b319171861464f6c445905e7649cb43bf9bc78be)
---
 sys/kern/kern_exit.c | 11 +++++------
 sys/kern/kern_time.c |  2 --
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 226cd5991261..e89139edc825 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -369,15 +369,14 @@ exit1(struct thread *td, int rval, int signo)
 	 * executing, prevent it from rearming itself and let it finish.
 	 */
 	if (timevalisset(&p->p_realtimer.it_value) &&
-	    _callout_stop_safe(&p->p_itcallout, CS_EXECUTING, NULL) == 0) {
+	    callout_stop(&p->p_itcallout) == 0) {
 		timevalclear(&p->p_realtimer.it_interval);
-		msleep(&p->p_itcallout, &p->p_mtx, PWAIT, "ritwait", 0);
-		KASSERT(!timevalisset(&p->p_realtimer.it_value),
-		    ("realtime timer is still armed"));
+		PROC_UNLOCK(p);
+		callout_drain(&p->p_itcallout);
+	} else {
+		PROC_UNLOCK(p);
 	}
 
-	PROC_UNLOCK(p);
-
 	if (p->p_sysent->sv_onexit != NULL)
 		p->p_sysent->sv_onexit(p);
 	seltdfini(td);
diff --git a/sys/kern/kern_time.c b/sys/kern/kern_time.c
index 0bab05c65ffc..b02b6a2021e0 100644
--- a/sys/kern/kern_time.c
+++ b/sys/kern/kern_time.c
@@ -952,8 +952,6 @@ realitexpire(void *arg)
 	kern_psignal(p, SIGALRM);
 	if (!timevalisset(&p->p_realtimer.it_interval)) {
 		timevalclear(&p->p_realtimer.it_value);
-		if (p->p_flag & P_WEXIT)
-			wakeup(&p->p_itcallout);
 		return;
 	}