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Subject[PATCH v2 3/6] signal: do_sigtimedwait() needs retarget_shared_pending()
do_sigtimedwait() changes current->blocked and thus it needs
set_current_blocked()->retarget_shared_pending().

We could use set_current_blocked() directly. It is fine to change
->real_blocked from all-zeroes to ->blocked and vice versa lockless,
but this is not immediately clear, looks racy, and needs a huge
comment to explain why this is correct.

To keep the things simple this patch adds the new static helper,
__set_task_blocked() which should be called with ->siglock held. This
way we can change both ->real_blocked and ->blocked atomically under
->siglock as the current code does. This is more understandable.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com>
---
kernel/signal.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)
--- sigprocmask/kernel/signal.c~3_sigtimedwait_retarget 2011-04-26 19:53:42.000000000 +0200
+++ sigprocmask/kernel/signal.c 2011-04-26 19:53:55.000000000 +0200
@@ -2115,11 +2115,8 @@ long do_no_restart_syscall(struct restar
return -EINTR;
}

-void set_current_blocked(const sigset_t *newset)
+static void __set_task_blocked(struct task_struct *tsk, const sigset_t *newset)
{
- struct task_struct *tsk = current;
-
- spin_lock_irq(&tsk->sighand->siglock);
if (signal_pending(tsk) && !thread_group_empty(tsk)) {
sigset_t newblocked;
signandsets(&newblocked, newset, &current->blocked);
@@ -2127,6 +2124,14 @@ void set_current_blocked(const sigset_t
}
tsk->blocked = *newset;
recalc_sigpending();
+}
+
+void set_current_blocked(const sigset_t *newset)
+{
+ struct task_struct *tsk = current;
+
+ spin_lock_irq(&tsk->sighand->siglock);
+ __set_task_blocked(tsk, newset);
spin_unlock_irq(&tsk->sighand->siglock);
}

@@ -2343,7 +2348,8 @@ int do_sigtimedwait(const sigset_t *whic
/*
* None ready, temporarily unblock those we're interested
* while we are sleeping in so that we'll be awakened when
- * they arrive.
+ * they arrive. Unblocking is always fine, we can avoid
+ * set_current_blocked().
*/
tsk->real_blocked = tsk->blocked;
sigandsets(&tsk->blocked, &tsk->blocked, &mask);
@@ -2353,10 +2359,9 @@ int do_sigtimedwait(const sigset_t *whic
timeout = schedule_timeout_interruptible(timeout);

spin_lock_irq(&tsk->sighand->siglock);
- sig = dequeue_signal(tsk, &mask, info);
- tsk->blocked = tsk->real_blocked;
+ __set_task_blocked(tsk, &tsk->real_blocked);
siginitset(&tsk->real_blocked, 0);
- recalc_sigpending();
+ sig = dequeue_signal(tsk, &mask, info);
}
spin_unlock_irq(&tsk->sighand->siglock);



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