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Fix a race condition between kern_wait() and thread_stopped().
Problem is in kern_wait(), parent process steps through children list,
once a child process is skipped, and later even if the child is stopped,
parent process still sleeps in msleep(), the race happens if parent
masked SIGCHLD.

Submitted by : Peter Edwards peadar.edwards at gmail dot com
MFC after    : 4 days
This commit is contained in:
David Xu 2005-04-19 08:11:28 +00:00
parent 95992d56f5
commit 407948a530
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=145261
1 changed files with 9 additions and 17 deletions
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26
sys/kern/kern_sig.c
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@ -85,7 +85,6 @@ static char *expand_name(const char *, uid_t, pid_t);
static int killpg1(struct thread *td, int sig, int pgid, int all);
static int issignal(struct thread *p);
static int sigprop(int sig);
static void stop(struct proc *);
static void tdsigwakeup(struct thread *td, int sig, sig_t action);
static int filt_sigattach(struct knote *kn);
static void filt_sigdetach(struct knote *kn);
@ -2249,21 +2248,6 @@ issignal(td)
/* NOTREACHED */
}
/*
* Put the argument process into the stopped state and notify the parent
* via wakeup. Signals are handled elsewhere. The process must not be
* on the run queue. Must be called with the proc p locked.
*/
static void
stop(struct proc *p)
{
PROC_LOCK_ASSERT(p, MA_OWNED);
p->p_flag |= P_STOPPED_SIG;
p->p_flag &= ~P_WAITED;
wakeup(p->p_pptr);
}
/*
* MPSAFE
*/
@ -2281,8 +2265,16 @@ thread_stopped(struct proc *p)
n++;
if ((p->p_flag & P_STOPPED_SIG) && (n == p->p_numthreads)) {
mtx_unlock_spin(&sched_lock);
stop(p);
p->p_flag &= ~P_WAITED;
PROC_LOCK(p->p_pptr);
/*
* Wake up parent sleeping in kern_wait(), also send
* SIGCHLD to parent, but SIGCHLD does not guarantee
* that parent will awake, because parent may masked
* the signal.
*/
p->p_pptr->p_flag |= P_STATCHILD;
wakeup(p->p_pptr);
ps = p->p_pptr->p_sigacts;
mtx_lock(&ps->ps_mtx);
if ((ps->ps_flag & PS_NOCLDSTOP) == 0) {