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Subject[PATCH v2 4/7] signal: sigprocmask: narrow the scope of ->siglock
No functional changes, preparation to simplify the review of the next change.

1. We can read current->block lockless, nobody else can ever change this mask.

2. Calculate the resulting sigset_t outside of ->siglock into the temporary
variable, then take ->siglock and change ->blocked.

Also, kill the stale comment about BKL.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

kernel/signal.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)

--- sigprocmask/kernel/signal.c~4_cleanup_sigprocmask 2011-04-17 21:28:21.000000000 +0200
+++ sigprocmask/kernel/signal.c 2011-04-17 22:16:44.000000000 +0200
@@ -2116,12 +2116,6 @@ long do_no_restart_syscall(struct restar
}

/*
- * We don't need to get the kernel lock - this is all local to this
- * particular thread.. (and that's good, because this is _heavily_
- * used by various programs)
- */
-
-/*
* This is also useful for kernel threads that want to temporarily
* (or permanently) block certain signals.
*
@@ -2131,30 +2125,33 @@ long do_no_restart_syscall(struct restar
*/
int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
{
- int error;
+ struct task_struct *tsk = current;
+ sigset_t newset;

- spin_lock_irq(&current->sighand->siglock);
+ /* Lockless, only current can change ->blocked, never from irq */
if (oldset)
- *oldset = current->blocked;
+ *oldset = tsk->blocked;

- error = 0;
switch (how) {
case SIG_BLOCK:
- sigorsets(&current->blocked, &current->blocked, set);
+ sigorsets(&newset, &tsk->blocked, set);
break;
case SIG_UNBLOCK:
- signandsets(&current->blocked, &current->blocked, set);
+ signandsets(&newset, &tsk->blocked, set);
break;
case SIG_SETMASK:
- current->blocked = *set;
+ newset = *set;
break;
default:
- error = -EINVAL;
+ return -EINVAL;
}
+
+ spin_lock_irq(&tsk->sighand->siglock);
+ tsk->blocked = newset;
recalc_sigpending();
- spin_unlock_irq(&current->sighand->siglock);
+ spin_unlock_irq(&tsk->sighand->siglock);

- return error;
+ return 0;
}

/**


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