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Add a knob to disable dequeueing SIGCHLD on waiting for live process

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It seems that Linux does not dequeue siginfo for SIGCHLD when wait*(2)
reports status of the running process.  In particular, sigwaitinfo(2)
and other signal querying syscalls can observe the siginfo after wait.

FreeBSD dequeued siginfo from the beginning, so we cannot change the
default ABI to be more compatible.  Still, add a knob to enable to
change to the other behavior for debugging purposes.

Reported by:	dchagin
Reviewed by:	dchagin, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D30675
This commit is contained in:
Konstantin Belousov 2021-06-05 21:24:35 +03:00
parent bc38762474
commit a12e901a5a
2 changed files with 12 additions and 3 deletions
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14
sys/kern/kern_exit.c
View file

@ -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) {

1
sys/sys/sysent.h
View file

@ -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))