git: 2ea2987d14d4 - stable/13 - Add a knob to disable dequeueing SIGCHLD on waiting for live process

[Konstantin Belousov]

The branch stable/13 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=2ea2987d14d4d58fc6afe15e790dc9aa075038cc

commit 2ea2987d14d4d58fc6afe15e790dc9aa075038cc
Author:     Konstantin Belousov <kib at FreeBSD.org>
AuthorDate: 2021-06-05 18:24:35 +0000
Commit:     Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-06-22 01:45:32 +0000

    Add a knob to disable dequeueing SIGCHLD on waiting for live process
    
    (cherry picked from commit a12e901a5a65417849c1ccf1e37b8d092fa438da)
---
 sys/kern/kern_exit.c | 14 +++++++++++---
 sys/sys/sysent.h     |  1 +
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index cb5996982a3a..fcd8b39a8ee2 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -105,6 +105,11 @@ SYSCTL_INT(_kern, OID_AUTO, kill_on_debugger_exit, CTLFLAG_RWTUN,
     &kern_kill_on_dbg_exit, 0,
     "Kill ptraced processes when debugger exits");
 
+static bool kern_wait_dequeue_sigchld = 1;
+SYSCTL_BOOL(_kern, OID_AUTO, wait_dequeue_sigchld, CTLFLAG_RWTUN,
+    &kern_wait_dequeue_sigchld, 0,
+    "Dequeue SIGCHLD on wait(2) for live process");
+
 struct proc *
 proc_realparent(struct proc *child)
 {
@@ -1207,9 +1212,12 @@ report_alive_proc(struct thread *td, struct proc *p, siginfo_t *siginfo,
 			p->p_flag &= ~P_CONTINUED;
 		else
 			p->p_flag |= P_WAITED;
-		PROC_LOCK(td->td_proc);
-		sigqueue_take(p->p_ksi);
-		PROC_UNLOCK(td->td_proc);
+		if (kern_wait_dequeue_sigchld &&
+		    (td->td_proc->p_sysent->sv_flags & SV_SIG_WAITNDQ) == 0) {
+			PROC_LOCK(td->td_proc);
+			sigqueue_take(p->p_ksi);
+			PROC_UNLOCK(td->td_proc);
+		}
 	}
 	sx_xunlock(&proctree_lock);
 	if (siginfo != NULL) {
diff --git a/sys/sys/sysent.h b/sys/sys/sysent.h
index 95e9dcb1a335..8b0903f7dcc0 100644
--- a/sys/sys/sysent.h
+++ b/sys/sys/sysent.h
@@ -162,6 +162,7 @@ struct sysentvec {
 #define	SV_ASLR		0x080000	/* ASLR allowed. */
 #define	SV_RNG_SEED_VER	0x100000	/* random(4) reseed generation. */
 #define	SV_SIG_DISCIGN	0x200000	/* Do not discard ignored signals */
+#define	SV_SIG_WAITNDQ	0x400000	/* Wait does not dequeue SIGCHLD */
 
 #define	SV_ABI_MASK	0xff
 #define	SV_PROC_FLAG(p, x)	((p)->p_sysent->sv_flags & (x))