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Restructure the code to handle reporting of non-exited processes from

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wait(2).
- Do not acquire the process spinlock if neither WTRAPPED nor WUNTRACED
  options were passed [1].
- Extract the code to report alive process into a new helper
  report_alive_proc() and use it for trapped, stopped and continued
  childrens.

Note that the process spinlock is required around the WTRAPPED and
WUNTRACED tests, because P_STOPPED_TRACE and P_STOPPED_SIG flags are
set before other threads are stopped at the suspension point, and that
threads increment p_suspcount while owning only the process spinlock,
the process lock is dropped by them.  If the spinlock is not taken for
tests, the syscall thread might miss both p_suspcount increment and
wakeup in wakeup in thread_suspend_switch().

Based on the submission by:	mjg [1]
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2016-12-04 20:44:58 +00:00
parent 6f1eb3052e
commit 435da98564
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=309539
1 changed files with 52 additions and 61 deletions
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113
sys/kern/kern_exit.c
View File

@ -1105,6 +1105,38 @@ kern_wait(struct thread *td, pid_t pid, int *status, int options,
return (ret);
}
static void
report_alive_proc(struct thread *td, struct proc *p, siginfo_t *siginfo,
int *status, int options, int si_code)
{
bool cont;
PROC_LOCK_ASSERT(p, MA_OWNED);
sx_assert(&proctree_lock, SA_XLOCKED);
MPASS(si_code == CLD_TRAPPED || si_code == CLD_STOPPED ||
si_code == CLD_CONTINUED);
cont = si_code == CLD_CONTINUED;
if ((options & WNOWAIT) == 0) {
if (cont)
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);
}
sx_xunlock(&proctree_lock);
if (siginfo != NULL) {
siginfo->si_code = si_code;
siginfo->si_status = cont ? SIGCONT : p->p_xsig;
}
if (status != NULL)
*status = cont ? SIGCONT : W_STOPCODE(p->p_xsig);
PROC_UNLOCK(p);
td->td_retval[0] = p->p_pid;
}
int
kern_wait6(struct thread *td, idtype_t idtype, id_t id, int *status,
int options, struct __wrusage *wrusage, siginfo_t *siginfo)
@ -1162,82 +1194,41 @@ kern_wait6(struct thread *td, idtype_t idtype, id_t id, int *status,
}
PROC_LOCK_ASSERT(p, MA_OWNED);
PROC_SLOCK(p);
if ((options & (WTRAPPED | WUNTRACED)) != 0)
PROC_SLOCK(p);
if ((options & WTRAPPED) != 0 &&
(p->p_flag & P_TRACED) != 0 &&
(p->p_flag & (P_STOPPED_TRACE | P_STOPPED_SIG)) != 0 &&
(p->p_suspcount == p->p_numthreads) &&
((p->p_flag & P_WAITED) == 0)) {
p->p_suspcount == p->p_numthreads &&
(p->p_flag & P_WAITED) == 0) {
PROC_SUNLOCK(p);
if ((options & WNOWAIT) == 0)
p->p_flag |= P_WAITED;
sx_xunlock(&proctree_lock);
if (status != NULL)
*status = W_STOPCODE(p->p_xsig);
if (siginfo != NULL) {
siginfo->si_status = p->p_xsig;
siginfo->si_code = CLD_TRAPPED;
}
if ((options & WNOWAIT) == 0) {
PROC_LOCK(q);
sigqueue_take(p->p_ksi);
PROC_UNLOCK(q);
}
CTR4(KTR_PTRACE,
"wait: returning trapped pid %d status %#x (xstat %d) xthread %d",
"wait: returning trapped pid %d status %#x "
"(xstat %d) xthread %d",
p->p_pid, W_STOPCODE(p->p_xsig), p->p_xsig,
p->p_xthread != NULL ? p->p_xthread->td_tid : -1);
PROC_UNLOCK(p);
td->td_retval[0] = pid;
p->p_xthread != NULL ?
p->p_xthread->td_tid : -1);
report_alive_proc(td, p, siginfo, status, options,
CLD_TRAPPED);
return (0);
}
}
if ((options & WUNTRACED) != 0 &&
(p->p_flag & P_STOPPED_SIG) != 0 &&
(p->p_suspcount == p->p_numthreads) &&
((p->p_flag & P_WAITED) == 0)) {
p->p_suspcount == p->p_numthreads &&
(p->p_flag & P_WAITED) == 0) {
PROC_SUNLOCK(p);
if ((options & WNOWAIT) == 0)
p->p_flag |= P_WAITED;
sx_xunlock(&proctree_lock);
if (status != NULL)
*status = W_STOPCODE(p->p_xsig);
if (siginfo != NULL) {
siginfo->si_status = p->p_xsig;
siginfo->si_code = CLD_STOPPED;
}
if ((options & WNOWAIT) == 0) {
PROC_LOCK(q);
sigqueue_take(p->p_ksi);
PROC_UNLOCK(q);
}
PROC_UNLOCK(p);
td->td_retval[0] = pid;
report_alive_proc(td, p, siginfo, status, options,
CLD_STOPPED);
return (0);
}
PROC_SUNLOCK(p);
if ((options & (WTRAPPED | WUNTRACED)) != 0)
PROC_SUNLOCK(p);
if ((options & WCONTINUED) != 0 &&
(p->p_flag & P_CONTINUED) != 0) {
sx_xunlock(&proctree_lock);
if ((options & WNOWAIT) == 0) {
p->p_flag &= ~P_CONTINUED;
PROC_LOCK(q);
sigqueue_take(p->p_ksi);
PROC_UNLOCK(q);
}
PROC_UNLOCK(p);
if (status != NULL)
*status = SIGCONT;
if (siginfo != NULL) {
siginfo->si_status = SIGCONT;
siginfo->si_code = CLD_CONTINUED;
}
td->td_retval[0] = pid;
report_alive_proc(td, p, siginfo, status, options,
CLD_CONTINUED);
return (0);
}
PROC_UNLOCK(p);