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Subject[PATCH] Additional/catchup RCU signal fixes for -mm
Hello!

Additional RCU signal fixes to cover a race with exec() and to add
some rcu_dereference()s from earlier patches.

Signed-off-by: <paulmck@us.ibm.com>

---
signal.c | 28 +++++++++++++++-------------
1 files changed, 15 insertions(+), 13 deletions(-)
diff -urpNa -X dontdiff linux-2.6.14-mm0/kernel/signal.c linux-2.6.14-mm0-fix/kernel/signal.c
--- linux-2.6.14-mm0/kernel/signal.c 2005-11-04 14:37:18.000000000 -0800
+++ linux-2.6.14-mm0-fix/kernel/signal.c 2005-11-04 17:23:40.000000000 -0800
@@ -337,7 +337,7 @@ void exit_sighand(struct task_struct *ts
write_lock_irq(&tasklist_lock);
rcu_read_lock();
if (tsk->sighand != NULL) {
- struct sighand_struct *sighand = tsk->sighand;
+ struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
spin_lock(&sighand->siglock);
__exit_sighand(tsk);
spin_unlock(&sighand->siglock);
@@ -352,13 +352,14 @@ void exit_sighand(struct task_struct *ts
void __exit_signal(struct task_struct *tsk)
{
struct signal_struct * sig = tsk->signal;
- struct sighand_struct * sighand = tsk->sighand;
+ struct sighand_struct * sighand;

if (!sig)
BUG();
if (!atomic_read(&sig->count))
BUG();
rcu_read_lock();
+ sighand = rcu_dereference(tsk->sighand);
spin_lock(&sighand->siglock);
posix_cpu_timers_exit(tsk);
if (atomic_dec_and_test(&sig->count)) {
@@ -1100,7 +1101,7 @@ void zap_other_threads(struct task_struc
}

/*
- * Must be called with the tasklist_lock held for reading!
+ * Must be called under rcu_read_lock() or with tasklist_lock read-held.
*/
int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
{
@@ -1386,7 +1387,7 @@ send_sigqueue(int sig, struct sigqueue *
{
unsigned long flags;
int ret = 0;
- struct sighand_struct *sh = p->sighand;
+ struct sighand_struct *sh;

BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

@@ -1405,7 +1406,15 @@ send_sigqueue(int sig, struct sigqueue *
goto out_err;
}

+retry:
+ sh = rcu_dereference(p->sighand);
+
spin_lock_irqsave(&sh->siglock, flags);
+ if (p->sighand != sh) {
+ /* We raced with exec() in a multithreaded process... */
+ spin_unlock_irqrestore(&sh->siglock, flags);
+ goto retry;
+ }

/*
* We do the check here again to handle the following scenario:
@@ -1464,15 +1473,8 @@ send_group_sigqueue(int sig, struct sigq

BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));

- while (!read_trylock(&tasklist_lock)) {
- if (!p->sighand)
- return -1;
- cpu_relax();
- }
- if (unlikely(!p->sighand)) {
- ret = -1;
- goto out_err;
- }
+ read_lock(&tasklist_lock);
+ /* Since it_lock is held, p->sighand cannot be NULL. */
spin_lock_irqsave(&p->sighand->siglock, flags);
handle_stop_signal(sig, p);

-
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