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authorTejun Heo <tj@kernel.org>2011-03-23 10:37:00 +0100
committerTejun Heo <tj@kernel.org>2011-03-23 10:37:00 +0100
commit39efa3ef3a376a4e53de2f82fc91182459d34200 (patch)
treef75a44fa77396edcf74e41686912554f96681340 /kernel/signal.c
parente5c1902e9260a0075ea52cb5ef627a8d9aaede89 (diff)
signal: Use GROUP_STOP_PENDING to stop once for a single group stop
Currently task->signal->group_stop_count is used to decide whether to stop for group stop. However, if there is a task in the group which is taking a long time to stop, other tasks which are continued by ptrace would repeatedly stop for the same group stop until the group stop is complete. Conversely, if a ptraced task is in TASK_TRACED state, the debugger won't get notified of group stops which is inconsistent compared to the ptraced task in any other state. This patch introduces GROUP_STOP_PENDING which tracks whether a task is yet to stop for the group stop in progress. The flag is set when a group stop starts and cleared when the task stops the first time for the group stop, and consulted whenever whether the task should participate in a group stop needs to be determined. Note that now tasks in TASK_TRACED also participate in group stop. This results in the following behavior changes. * For a single group stop, a ptracer would see at most one stop reported. * A ptracee in TASK_TRACED now also participates in group stop and the tracer would get the notification. However, as a ptraced task could be in TASK_STOPPED state or any ptrace trap could consume group stop, the notification may still be missing. These will be addressed with further patches. * A ptracee may start a group stop while one is still in progress if the tracer let it continue with stop signal delivery. Group stop code handles this correctly. Oleg: * Spotted that a task might skip signal check even when its GROUP_STOP_PENDING is set. Fixed by updating recalc_sigpending_tsk() to check GROUP_STOP_PENDING instead of group_stop_count. * Pointed out that task->group_stop should be cleared whenever task->signal->group_stop_count is cleared. Fixed accordingly. * Pointed out the behavior inconsistency between TASK_TRACED and RUNNING and the last behavior change. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: Roland McGrath <roland@redhat.com>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c36
1 files changed, 21 insertions, 15 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index ecb20089eaf..a2e7a6527d2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -124,7 +124,7 @@ static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
static int recalc_sigpending_tsk(struct task_struct *t)
{
- if (t->signal->group_stop_count > 0 ||
+ if ((t->group_stop & GROUP_STOP_PENDING) ||
PENDING(&t->pending, &t->blocked) ||
PENDING(&t->signal->shared_pending, &t->blocked)) {
set_tsk_thread_flag(t, TIF_SIGPENDING);
@@ -232,19 +232,19 @@ static inline void print_dropped_signal(int sig)
* CONTEXT:
* Must be called with @task->sighand->siglock held.
*/
-static void task_clear_group_stop_pending(struct task_struct *task)
+void task_clear_group_stop_pending(struct task_struct *task)
{
- task->group_stop &= ~GROUP_STOP_CONSUME;
+ task->group_stop &= ~(GROUP_STOP_PENDING | GROUP_STOP_CONSUME);
}
/**
* task_participate_group_stop - participate in a group stop
* @task: task participating in a group stop
*
- * @task is participating in a group stop. Group stop states are cleared
- * and the group stop count is consumed if %GROUP_STOP_CONSUME was set. If
- * the consumption completes the group stop, the appropriate %SIGNAL_*
- * flags are set.
+ * @task has GROUP_STOP_PENDING set and is participating in a group stop.
+ * Group stop states are cleared and the group stop count is consumed if
+ * %GROUP_STOP_CONSUME was set. If the consumption completes the group
+ * stop, the appropriate %SIGNAL_* flags are set.
*
* CONTEXT:
* Must be called with @task->sighand->siglock held.
@@ -254,6 +254,8 @@ static bool task_participate_group_stop(struct task_struct *task)
struct signal_struct *sig = task->signal;
bool consume = task->group_stop & GROUP_STOP_CONSUME;
+ WARN_ON_ONCE(!(task->group_stop & GROUP_STOP_PENDING));
+
task_clear_group_stop_pending(task);
if (!consume)
@@ -765,6 +767,9 @@ static int prepare_signal(int sig, struct task_struct *p, int from_ancestor_ns)
t = p;
do {
unsigned int state;
+
+ task_clear_group_stop_pending(t);
+
rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
/*
* If there is a handler for SIGCONT, we must make
@@ -906,6 +911,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
signal->group_stop_count = 0;
t = p;
do {
+ task_clear_group_stop_pending(t);
sigaddset(&t->pending.signal, SIGKILL);
signal_wake_up(t, 1);
} while_each_thread(p, t);
@@ -1139,6 +1145,7 @@ int zap_other_threads(struct task_struct *p)
p->signal->group_stop_count = 0;
while_each_thread(p, t) {
+ task_clear_group_stop_pending(t);
count++;
/* Don't bother with already dead threads */
@@ -1690,7 +1697,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
* If there is a group stop in progress,
* we must participate in the bookkeeping.
*/
- if (current->signal->group_stop_count > 0)
+ if (current->group_stop & GROUP_STOP_PENDING)
task_participate_group_stop(current);
current->last_siginfo = info;
@@ -1775,8 +1782,8 @@ static int do_signal_stop(int signr)
struct signal_struct *sig = current->signal;
int notify = 0;
- if (!sig->group_stop_count) {
- unsigned int gstop = GROUP_STOP_CONSUME;
+ if (!(current->group_stop & GROUP_STOP_PENDING)) {
+ unsigned int gstop = GROUP_STOP_PENDING | GROUP_STOP_CONSUME;
struct task_struct *t;
if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
@@ -1796,8 +1803,7 @@ static int do_signal_stop(int signr)
* stop is always done with the siglock held,
* so this check has no races.
*/
- if (!(t->flags & PF_EXITING) &&
- !task_is_stopped_or_traced(t)) {
+ if (!(t->flags & PF_EXITING) && !task_is_stopped(t)) {
t->group_stop = gstop;
sig->group_stop_count++;
signal_wake_up(t, 0);
@@ -1926,8 +1932,8 @@ relock:
if (unlikely(signr != 0))
ka = return_ka;
else {
- if (unlikely(signal->group_stop_count > 0) &&
- do_signal_stop(0))
+ if (unlikely(current->group_stop &
+ GROUP_STOP_PENDING) && do_signal_stop(0))
goto relock;
signr = dequeue_signal(current, &current->blocked,
@@ -2073,7 +2079,7 @@ void exit_signals(struct task_struct *tsk)
if (!signal_pending(t) && !(t->flags & PF_EXITING))
recalc_sigpending_and_wake(t);
- if (unlikely(tsk->signal->group_stop_count) &&
+ if (unlikely(tsk->group_stop & GROUP_STOP_PENDING) &&
task_participate_group_stop(tsk))
group_stop = CLD_STOPPED;
out: