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>
Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>
Acked-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index 707736e..e8308e3 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2299,12 +2299,6 @@ long do_no_restart_syscall(struct restart_block *param)
        return -EINTR;
 }
 
-/*
- * 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.
@@ -2315,30 +2309,33 @@ long do_no_restart_syscall(struct restart_block *param)
  */
 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;
 }
 
 /**