Two threads, T1 and T2, SIGTTIN is SIG_DFL, SIGTTOU has a handler.
T1 does get_signal_to_deliver(), dequeus SIGTTIN, unlocks ->siglock.
SIGCONT comes in, nothing to do yet, just clear SIGNAL_STOP_DEQUEUED.
SIGTTOU is sent, T2 dequeues it and sets SIGNAL_STOP_DEQUEUED again.
It has a handler, we shouldn't stop, but
T1 continues, takes ->siglock, and calls do_signal_stop().
Move the setting of SIGNAL_STOP_DEQUEUED from dequeue_signal() to
get_signal_to_deliver(), and set this flag only if we are really going to stop.
This also simplifies the code and makes the SIGNAL_STOP_DEQUEUED usage more
understandable.
However, this changes the behaviour when the task is ptraced. If the debugger
doesn't clear ->exit_code, SIGSTOP always succeeds after ptrace_stop(), even
if SIGCONT was sent in between. I can't decide whether this change is good
or bad, hopefully Roland can clarify.
Signed-off-by: Oleg Nesterov <[email protected]>
--- t/kernel/signal.c~S_G_S 2007-08-23 16:02:57.000000000 +0400
+++ t/kernel/signal.c 2007-08-28 19:15:28.000000000 +0400
@@ -409,22 +409,7 @@ int dequeue_signal(struct task_struct *t
}
if (likely(tsk == current))
recalc_sigpending();
- if (signr && unlikely(sig_kernel_stop(signr))) {
- /*
- * Set a marker that we have dequeued a stop signal. Our
- * caller might release the siglock and then the pending
- * stop signal it is about to process is no longer in the
- * pending bitmasks, but must still be cleared by a SIGCONT
- * (and overruled by a SIGKILL). So those cases clear this
- * shared flag after we've set it. Note that this flag may
- * remain set after the signal we return is ignored or
- * handled. That doesn't matter because its only purpose
- * is to alert stop-signal processing code when another
- * processor has come along and cleared the flag.
- */
- if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
- tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
- }
+
if (signr && likely(tsk == current) &&
((info->si_code & __SI_MASK) == __SI_TIMER) &&
info->si_sys_private){
@@ -1683,9 +1668,6 @@ static int do_signal_stop(int signr)
struct signal_struct *sig = current->signal;
int stop_count;
- if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED))
- return 0;
-
if (sig->group_stop_count > 0) {
/*
* There is a group stop in progress. We don't need to
@@ -1849,6 +1831,9 @@ relock:
continue;
if (sig_kernel_stop(signr)) {
+ if (current->signal->flags & SIGNAL_GROUP_EXIT)
+ continue;
+
/*
* The default action is to stop all threads in
* the thread group. The job control signals
@@ -1860,14 +1845,20 @@ relock:
* We need to check for that and bail out if necessary.
*/
if (signr != SIGSTOP) {
+ /*
+ * Set a marker that we have dequeued a stop
+ * signal. We are going to unlock ->siglock,
+ * another signal can cancel group stop request
+ * during this window. In that case this marker
+ * will be cleared when we re-check below.
+ */
+ current->signal->flags |= SIGNAL_STOP_DEQUEUED;
spin_unlock_irq(¤t->sighand->siglock);
-
- /* signals can be posted during this window */
-
if (is_current_pgrp_orphaned())
goto relock;
-
spin_lock_irq(¤t->sighand->siglock);
+ if (!(current->signal->flags & SIGNAL_STOP_DEQUEUED))
+ continue;
}
if (likely(do_signal_stop(signr))) {
-
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