Messages in this thread Patch in this message | | | Date | Sun, 19 Jun 2005 20:13:06 +0400 | From | Oleg Nesterov <> | Subject | [PATCH] de_thread: eliminate unneccessary sighand locking |
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while switching current->sighand de_thread does:
write_lock_irq(&tasklist_lock); spin_lock(&oldsighand->siglock); spin_lock(&newsighand->siglock);
current->sighand = newsighand; recalc_sigpending();
Is these 2 sighand locks are really needed?
At this moment we already zapped other threads, so nobody can access newsighand via current->. And we are holding tasklist_lock, so other processes can't send signals to us or use our ->sighand in any way.
oldsighand can be seen from CLONE_SIGHAND processes, but we are not using oldsighand in any way, so this lock seems to be unneeded too.
The only possibility that I can imagine is that some process does: read_lock(tasklist_lock); task = find_task(); spin_lock(task->sighand->siglock); read_unlock(tasklist_lock); play with task->signal
Is this possible/allowed?
And why do we need recalc_sigpending() ? We are not changing ->pending or ->blocked, just ->sighand.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 2.6.12/fs/exec.c~ 2005-05-09 16:37:16.000000000 +0400 +++ 2.6.12/fs/exec.c 2005-06-20 00:03:24.000000000 +0400 @@ -758,14 +758,7 @@ no_thread_group: sizeof(newsighand->action)); write_lock_irq(&tasklist_lock); - spin_lock(&oldsighand->siglock); - spin_lock(&newsighand->siglock); - current->sighand = newsighand; - recalc_sigpending(); - - spin_unlock(&newsighand->siglock); - spin_unlock(&oldsighand->siglock); write_unlock_irq(&tasklist_lock); if (atomic_dec_and_test(&oldsighand->count)) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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