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authorOleg Nesterov <oleg@redhat.com>2011-04-27 20:59:41 +0200
committerOleg Nesterov <oleg@redhat.com>2011-04-28 13:01:37 +0200
commite6fa16ab9c1e9b344428e6fea4d29e3cc4b28fb0 (patch)
treec1bdacc0537213cba8ba75a63ac286e21c0a7250 /kernel/signal.c
parent73ef4aeb61b53fce464a7e24ef03a26f98b2f617 (diff)
signal: sigprocmask() should do retarget_shared_pending()
In short, almost every changing of current->blocked is wrong, or at least can lead to the unexpected results. For example. Two threads T1 and T2, T1 sleeps in sigtimedwait/pause/etc. kill(tgid, SIG) can pick T2 for TIF_SIGPENDING. If T2 calls sigprocmask() and blocks SIG before it notices the pending signal, nobody else can handle this pending shared signal. I am not sure this is bug, but at least this looks strange imho. T1 should not sleep forever, there is a signal which should wake it up. This patch moves the code which actually changes ->blocked into the new helper, set_current_blocked() and changes this code to call retarget_shared_pending() as exit_signals() does. We should only care about the signals we just blocked, we use "newset & ~current->blocked" as a mask. We do not check !sigisemptyset(newblocked), retarget_shared_pending() is cheap unless mask & shared_pending. Note: for this particular case we could simply change sigprocmask() to return -EINTR if signal_pending(), but then we should change other callers and, more importantly, if we need this fix then set_current_blocked() will have more callers and some of them can't restart. See the next patch as a random example. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Matt Fleming <matt.fleming@linux.intel.com> Acked-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c29
1 files changed, 24 insertions, 5 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index e8308e3238c1..8aa3a2e226af 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2299,6 +2299,29 @@ long do_no_restart_syscall(struct restart_block *param)
return -EINTR;
}
+/**
+ * set_current_blocked - change current->blocked mask
+ * @newset: new mask
+ *
+ * It is wrong to change ->blocked directly, this helper should be used
+ * to ensure the process can't miss a shared signal we are going to block.
+ */
+void set_current_blocked(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;
+ /* A set of now blocked but previously unblocked signals. */
+ signandsets(&newblocked, newset, &current->blocked);
+ retarget_shared_pending(tsk, &newblocked);
+ }
+ tsk->blocked = *newset;
+ recalc_sigpending();
+ spin_unlock_irq(&tsk->sighand->siglock);
+}
+
/*
* This is also useful for kernel threads that want to temporarily
* (or permanently) block certain signals.
@@ -2330,11 +2353,7 @@ int sigprocmask(int how, sigset_t *set, sigset_t *oldset)
return -EINVAL;
}
- spin_lock_irq(&tsk->sighand->siglock);
- tsk->blocked = newset;
- recalc_sigpending();
- spin_unlock_irq(&tsk->sighand->siglock);
-
+ set_current_blocked(&newset);
return 0;
}