The patch titled
handle_stop_signal: don't wake up the stopped task until it sees SIGCONT
has been added to the -mm tree. Its filename is
handle_stop_signal-dont-wake-up-the-stopped-task-until-it-sees-sigcont.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: handle_stop_signal: don't wake up the stopped task until it sees SIGCONT
From: Oleg Nesterov <oleg@xxxxxxxxxx>
The bug was found by Jiri Kosina and the patch is based on his ideas.
handle_stop_signal(SIGCONT) wakes up the stopped task and unlocks ->siglock
for do_notify_parent_cldstop(p, CLD_CONTINUED). The woken task returns from
do_signal_stop(), takes ->siglock and resumes to user-space without actually
seeing SIGCONT which may have a handler.
Move the code realated to do_notify_parent_cldstop(CLD_CONTINUED) up, before
"wake_up_state(t, state)".
NOTE: It is possible that the subsequent rm_from_queue(SIG_KERNEL_STOP_MASK)
removes SIGSTOP which comes after SIGCONT when we drop ->siglock. Not nice,
but possible even without this change. Hopefully we can remove the parent
notifying code from the sender path completely, but this needs more thinking.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 40 ++++++++++++++++++++--------------------
1 file changed, 20 insertions(+), 20 deletions(-)
diff -puN kernel/signal.c~handle_stop_signal-dont-wake-up-the-stopped-task-until-it-sees-sigcont kernel/signal.c
--- a/kernel/signal.c~handle_stop_signal-dont-wake-up-the-stopped-task-until-it-sees-sigcont
+++ a/kernel/signal.c
@@ -600,12 +600,31 @@ static void handle_stop_signal(int sig,
do_notify_parent_cldstop(p, CLD_STOPPED);
spin_lock(&p->sighand->siglock);
}
+
+ if (p->signal->flags & SIGNAL_STOP_STOPPED) {
+ /*
+ * We were in fact stopped, and are now continued.
+ * Notify the parent with CLD_CONTINUED.
+ */
+ p->signal->flags = SIGNAL_STOP_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;
+ }
+
rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
t = p;
do {
unsigned int state;
rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
-
/*
* If there is a handler for SIGCONT, we must make
* sure that no thread returns to user mode before
@@ -629,25 +648,6 @@ static void handle_stop_signal(int sig,
t = next_thread(t);
} while (t != p);
-
- if (p->signal->flags & SIGNAL_STOP_STOPPED) {
- /*
- * We were in fact stopped, and are now continued.
- * Notify the parent with CLD_CONTINUED.
- */
- p->signal->flags = SIGNAL_STOP_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;
- }
} else if (sig == SIGKILL) {
/*
* Make sure that any pending stop signal already dequeued
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
git-hrt.patch
kthread-add-a-missing-memory-barrier-to-kthread_stop.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
documentation-atomic_add_unless-doesnt-imply-mb-on-failure-fix.patch
handle_stop_signal-dont-wake-up-the-stopped-task-until-it-sees-sigcont.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
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
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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