diff options
| author | Oleg Nesterov <oleg@tv-sign.ru> | 2008-04-30 00:52:44 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-04-30 08:29:34 -0700 |
| commit | e442055193e4584218006e616c9bdce0c5e9ae5c (patch) | |
| tree | 5e444253953c2f48c0a194bf8c5799f03bb2e266 /include/linux | |
| parent | 3b5e9e53c6f31b5a5a0f5c43707503c62bdefa46 (diff) | |
signals: re-assign CLD_CONTINUED notification from the sender to reciever
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@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/sched.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index 1d02babdb2c..ef561527034 100644 --- a/include/linux/sched.h +++ b/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) |