The patch titled
fix group stop with exit race
has been added to the -mm tree. Its filename is
fix-group-stop-with-exit-race.patch
*** 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
------------------------------------------------------
Subject: fix group stop with exit race
From: Oleg Nesterov <oleg@xxxxxxxxxx>
do_signal_stop() counts all sub-thread and sets ->group_stop_count
accordingly. Every thread should decrement ->group_stop_count and stop,
the last one should notify the parent.
However a sub-thread can exit before it notices the signal_pending(), or it
may be somewhere in do_exit() already. In that case the group stop never
finishes properly.
Note: this is a minimal fix, we can add some optimizations later. Say we
can return quickly if thread_group_empty(). Also, we can move some signal
related code from exit_notify() to exit_signals().
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/signal.h | 1 +
kernel/exit.c | 2 +-
kernel/signal.c | 27 ++++++++++++++++++++++++++-
3 files changed, 28 insertions(+), 2 deletions(-)
diff -puN include/linux/signal.h~fix-group-stop-with-exit-race include/linux/signal.h
--- a/include/linux/signal.h~fix-group-stop-with-exit-race
+++ a/include/linux/signal.h
@@ -241,6 +241,7 @@ extern int show_unhandled_signals;
struct pt_regs;
extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie);
+extern void exit_signals(struct task_struct *tsk);
extern struct kmem_cache *sighand_cachep;
diff -puN kernel/exit.c~fix-group-stop-with-exit-race kernel/exit.c
--- a/kernel/exit.c~fix-group-stop-with-exit-race
+++ a/kernel/exit.c
@@ -945,7 +945,7 @@ fastcall NORET_TYPE void do_exit(long co
schedule();
}
- tsk->flags |= PF_EXITING;
+ exit_signals(tsk); /* sets PF_EXITING */
/*
* tsk->flags are checked in the futex code to protect against
* an exiting task cleaning up the robust pi futexes.
diff -puN kernel/signal.c~fix-group-stop-with-exit-race kernel/signal.c
--- a/kernel/signal.c~fix-group-stop-with-exit-race
+++ a/kernel/signal.c
@@ -1707,7 +1707,7 @@ static int do_signal_stop(int signr)
* stop is always done with the siglock held,
* so this check has no races.
*/
- if (!t->exit_state &&
+ if (!(t->flags & PF_EXITING) &&
!is_task_stopped_or_traced(t)) {
stop_count++;
signal_wake_up(t, 0);
@@ -1868,6 +1868,31 @@ relock:
return signr;
}
+void exit_signals(struct task_struct *tsk)
+{
+ int group_stop = 0;
+
+ spin_lock_irq(&tsk->sighand->siglock);
+ if (unlikely(tsk->signal->group_stop_count) &&
+ !--tsk->signal->group_stop_count) {
+ tsk->signal->flags = SIGNAL_STOP_STOPPED;
+ group_stop = 1;
+ }
+
+ /*
+ * From now this task is not visible for group-wide signals,
+ * see wants_signal(), do_signal_stop().
+ */
+ tsk->flags |= PF_EXITING;
+ spin_unlock_irq(&tsk->sighand->siglock);
+
+ if (unlikely(group_stop)) {
+ read_lock(&tasklist_lock);
+ do_notify_parent_cldstop(tsk, CLD_STOPPED);
+ read_unlock(&tasklist_lock);
+ }
+}
+
EXPORT_SYMBOL(recalc_sigpending);
EXPORT_SYMBOL_GPL(dequeue_signal);
EXPORT_SYMBOL(flush_signals);
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
fix-cloneclone_newpid.patch
__group_complete_signal-fix-coredump-with-group-stop-race.patch
remove-handle_group_stop-in-favor-of-do_signal_stop.patch
exec-rework-the-group-exit-and-fix-the-race-with-kill.patch
git-sched.patch
use-__set_task_state-for-traced-stopped-tasks.patch
add-task_wakekill.patch
do_wait-remove-one-else-if-branch.patch
proc-implement-proc_single_file_operations.patch
proc-rewrite-do_task_stat-to-correctly-handle-pid-namespaces.patch
proc-seqfile-convert-proc_pid_statm.patch
proc-proper-pidns-handling-for-proc-self.patch
proc-fix-the-threaded-proc-self.patch
kill-pt_attached.patch
kill-my_ptrace_child.patch
ptrace_check_attach-remove-unneeded-signal-=-null-check.patch
ptrace_stop-fix-the-race-with-ptrace-detachattach.patch
wait_task_stopped-simplify-and-fix-races-with-sigcont-sigkill-untrace.patch
do_wait-factor-out-retval-=-0-checks.patch
ptrace_stop-fix-racy-nonstop_code-setting.patch
wait_task_stopped-remove-unneeded-delay_group_leader-check.patch
do_wait-cleanup-delay_group_leader-usage.patch
do_wait-fix-security-checks.patch
do_wait-fix-security-checks-fix.patch
wait_task_continued-zombie-dont-use-task_pid_nr_ns-lockless.patch
wait_task_zombie-remove-exit_state-exit_signal-checks-for-wnowait.patch
sys_setpgid-simplify-pid-ns-interaction.patch
fix-setsid-for-sub-namespace-sbin-init.patch
teach-set_special_pids-to-use-struct-pid.patch
move-daemonized-kernel-threads-into-the-swappers-session.patch
start-the-global-sbin-init-with-00-special-pids.patch
fix-group-stop-with-exit-race.patch
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