The patch titled
signals: re-assign CLD_CONTINUED notification from the sender to reciever
has been added to the -mm tree. Its filename is
signals-re-assign-cld_continued-notification-from-the-sender-to-reciever.patch
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------------------------------------------------------
Subject: signals: re-assign CLD_CONTINUED notification from the sender to reciever
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Based on discussion with Jiri and Roland.
In short: currently handle_stop_signal(SIGCONT, p) sends the notification to
p->parent, with this patch p itself notifies its parent when it becomes
running.
handle_stop_signal(SIGCONT) has to drop ->siglock temporary in order to notify
the parent with do_notify_parent_cldstop(). This leads to multiple problems:
- as Jiri Kosina pointed out, the stopped task can resume without
actually seeing SIGCONT which may have a handler.
- we race with another sig_kernel_stop() signal which may come in
that window.
- we race with sig_fatal() signals which may set SIGNAL_GROUP_EXIT
in that window.
- we can't avoid taking tasklist_lock() while sending SIGCONT.
With this patch handle_stop_signal() just sets the new SIGNAL_CLD_CONTINUED
flag in p->signal->flags and returns. The notification is sent by the first
task which returns from finish_stop() (there should be at least one) or any
other signalled thread from get_signal_to_deliver().
This is a user-visible change. Say, currently kill(SIGCONT, stopped_child)
can't return without seeing SIGCHLD, with this patch SIGCHLD can be delayed
unpredictably. Another difference is that if the child is ptraced by another
process, CLD_CONTINUED may be delivered to ->real_parent after ptrace_detach()
while currently it always goes to the tracer which doesn't actually need this
notification. Hopefully not a problem.
The patch asks for the futher obvious cleanups, I'll send them separately.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 6 ++++++
kernel/signal.c | 29 +++++++++++++++++++----------
2 files changed, 25 insertions(+), 10 deletions(-)
diff -puN include/linux/sched.h~signals-re-assign-cld_continued-notification-from-the-sender-to-reciever include/linux/sched.h
--- a/include/linux/sched.h~signals-re-assign-cld_continued-notification-from-the-sender-to-reciever
+++ a/include/linux/sched.h
@@ -554,6 +554,12 @@ struct signal_struct {
#define SIGNAL_STOP_DEQUEUED 0x00000002 /* stop signal dequeued */
#define SIGNAL_STOP_CONTINUED 0x00000004 /* SIGCONT since WCONTINUED reap */
#define SIGNAL_GROUP_EXIT 0x00000008 /* group exit in progress */
+/*
+ * Pending notifications to parent.
+ */
+#define SIGNAL_CLD_STOPPED 0x00000010
+#define SIGNAL_CLD_CONTINUED 0x00000020
+#define SIGNAL_CLD_MASK (SIGNAL_CLD_STOPPED|SIGNAL_CLD_CONTINUED)
/* If true, all threads except ->group_exit_task have pending SIGKILL */
static inline int signal_group_exit(const struct signal_struct *sig)
diff -puN kernel/signal.c~signals-re-assign-cld_continued-notification-from-the-sender-to-reciever kernel/signal.c
--- a/kernel/signal.c~signals-re-assign-cld_continued-notification-from-the-sender-to-reciever
+++ a/kernel/signal.c
@@ -603,10 +603,8 @@ static void handle_stop_signal(int sig,
* the SIGCHLD was pending on entry to this kill.
*/
p->signal->group_stop_count = 0;
- p->signal->flags = SIGNAL_STOP_CONTINUED;
- spin_unlock(&p->sighand->siglock);
- do_notify_parent_cldstop(p, CLD_STOPPED);
- spin_lock(&p->sighand->siglock);
+ p->signal->flags = SIGNAL_STOP_CONTINUED |
+ SIGNAL_CLD_STOPPED;
}
rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
t = p;
@@ -643,25 +641,23 @@ static void handle_stop_signal(int sig,
* We were in fact stopped, and are now continued.
* Notify the parent with CLD_CONTINUED.
*/
- p->signal->flags = SIGNAL_STOP_CONTINUED;
+ p->signal->flags = SIGNAL_STOP_CONTINUED |
+ SIGNAL_CLD_CONTINUED;
p->signal->group_exit_code = 0;
- spin_unlock(&p->sighand->siglock);
- do_notify_parent_cldstop(p, CLD_CONTINUED);
- spin_lock(&p->sighand->siglock);
} else {
/*
* We are not stopped, but there could be a stop
* signal in the middle of being processed after
* being removed from the queue. Clear that too.
*/
- p->signal->flags = 0;
+ p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
}
} else if (sig == SIGKILL) {
/*
* Make sure that any pending stop signal already dequeued
* is undone by the wakeup for SIGKILL.
*/
- p->signal->flags = 0;
+ p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
}
}
@@ -1745,6 +1741,19 @@ relock:
try_to_freeze();
spin_lock_irq(¤t->sighand->siglock);
+
+ if (unlikely(current->signal->flags & SIGNAL_CLD_MASK)) {
+ int why = (current->signal->flags & SIGNAL_STOP_CONTINUED)
+ ? CLD_CONTINUED : CLD_STOPPED;
+ current->signal->flags &= ~SIGNAL_CLD_MASK;
+ spin_unlock_irq(¤t->sighand->siglock);
+
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(current->group_leader, why);
+ read_unlock(&tasklist_lock);
+ goto relock;
+ }
+
for (;;) {
struct k_sigaction *ka;
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
git-hrt.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
mmap_region-cleanup-the-final-vma_merge-related-code.patch
remove-unused-variable-from-send_signal.patch
turn-legacy_queue-macro-into-static-inline-function.patch
consolidate-checking-for-ignored-legacy-signals.patch
consolidate-checking-for-ignored-legacy-signals-simplify.patch
signals-do_signal_stop-use-signal_group_exit.patch
signals-do_group_exit-use-signal_group_exit-more-consistently.patch
lock_task_sighand-add-rcu-lock-unlock.patch
k_getrusage-dont-take-rcu_read_lock.patch
do_task_stat-dont-take-rcu_read_lock.patch
signals-consolidate-checks-for-whether-or-not-to-ignore-a-signal.patch
signals-clean-dequeue_signal-from-excess-checks-and-assignments.patch
signals-consolidate-send_sigqueue-and-send_group_sigqueue.patch
signals-cleanup-security_task_kill-usage-implementation.patch
signals-re-assign-cld_continued-notification-from-the-sender-to-reciever.patch
ptrace-introduce-task_detached-helper.patch
ptrace-introduce-ptrace_reparented-helper.patch
reparent_thread-use-same_thread_group.patch
document-de_thread-with-exit_notify-connection.patch
workqueues-shrink-cpu_populated_map-when-cpu-dies.patch
workqueues-shrink-cpu_populated_map-when-cpu-dies-fix.patch
cleanup_workqueue_thread-remove-the-unneeded-cpu-parameter.patch
simplify-cpu_hotplug_begin-put_online_cpus.patch
redo-locking-of-tty-pgrp.patch
resume-tty-on-susp-and-fix-crnl-order-in-n_tty-line-discipline.patch
tty_io-fix-remaining-pid-struct-locking.patch
tty_io-fix-remaining-pid-struct-locking-small-cleanup.patch
procfs-task-exe-symlink.patch
procfs-task-exe-symlink-fix.patch
procfs-task-exe-symlink-fix-2.patch
free_pidmap-turn-it-into-free_pidmapstruct-upid.patch
put_pid-make-sure-we-dont-free-the-live-pid.patch
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