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[PATCH] do_signal_stop: don't take tasklist_lock

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do_signal_stop() does not need tasklist_lock anymore.  So it does not need to
do misc re-checks, and we can simplify the code.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-03-28 16:11:22 -08:00 committed by Linus Torvalds
parent 6108ccd3e2
commit a122b341b7
1 changed files with 20 additions and 55 deletions
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75
kernel/signal.c
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@ -1682,8 +1682,7 @@ out:
* Returns nonzero if we've actually stopped and released the siglock.
* Returns zero if we didn't stop and still hold the siglock.
*/
static int
do_signal_stop(int signr)
static int do_signal_stop(int signr)
{
struct signal_struct *sig = current->signal;
struct sighand_struct *sighand = current->sighand;
@ -1703,7 +1702,6 @@ do_signal_stop(int signr)
set_current_state(TASK_STOPPED);
if (stop_count == 0)
sig->flags = SIGNAL_STOP_STOPPED;
spin_unlock_irq(&sighand->siglock);
}
else if (thread_group_empty(current)) {
/*
@ -1712,71 +1710,38 @@ do_signal_stop(int signr)
current->exit_code = current->signal->group_exit_code = signr;
set_current_state(TASK_STOPPED);
sig->flags = SIGNAL_STOP_STOPPED;
spin_unlock_irq(&sighand->siglock);
}
else {
/*
* (sig->group_stop_count == 0)
* There is no group stop already in progress.
* We must initiate one now, but that requires
* dropping siglock to get both the tasklist lock
* and siglock again in the proper order. Note that
* this allows an intervening SIGCONT to be posted.
* We need to check for that and bail out if necessary.
* We must initiate one now.
*/
struct task_struct *t;
spin_unlock_irq(&sighand->siglock);
/* signals can be posted during this window */
read_lock(&tasklist_lock);
spin_lock_irq(&sighand->siglock);
if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED)) {
/*
* Another stop or continue happened while we
* didn't have the lock. We can just swallow this
* signal now. If we raced with a SIGCONT, that
* should have just cleared it now. If we raced
* with another processor delivering a stop signal,
* then the SIGCONT that wakes us up should clear it.
*/
read_unlock(&tasklist_lock);
return 0;
}
if (sig->group_stop_count == 0) {
sig->group_exit_code = signr;
stop_count = 0;
for (t = next_thread(current); t != current;
t = next_thread(t))
/*
* Setting state to TASK_STOPPED for a group
* stop is always done with the siglock held,
* so this check has no races.
*/
if (!t->exit_state &&
!(t->state & (TASK_STOPPED|TASK_TRACED))) {
stop_count++;
signal_wake_up(t, 0);
}
sig->group_stop_count = stop_count;
}
else {
/* A race with another thread while unlocked. */
signr = sig->group_exit_code;
stop_count = --sig->group_stop_count;
}
current->exit_code = signr;
sig->group_exit_code = signr;
stop_count = 0;
for (t = next_thread(current); t != current; t = next_thread(t))
/*
* Setting state to TASK_STOPPED for a group
* stop is always done with the siglock held,
* so this check has no races.
*/
if (!t->exit_state &&
!(t->state & (TASK_STOPPED|TASK_TRACED))) {
stop_count++;
signal_wake_up(t, 0);
}
sig->group_stop_count = stop_count;
set_current_state(TASK_STOPPED);
if (stop_count == 0)
sig->flags = SIGNAL_STOP_STOPPED;
spin_unlock_irq(&sighand->siglock);
read_unlock(&tasklist_lock);
}
spin_unlock_irq(&sighand->siglock);
finish_stop(stop_count);
return 1;
}