epoll: don't use current in irq context
ep_call_nested() (formerly ep_poll_safewake()) uses "current" (without
dereferencing it) to detect callback recursion, but it may be called from
irq context where the use of current is generally discouraged. It would
be better to use get_cpu() and put_cpu() to detect the callback recursion.
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 205a1e1..db4365f 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -97,8 +97,8 @@
*/
struct nested_call_node {
struct list_head llink;
- struct task_struct *task;
void *cookie;
+ int cpu;
};
/*
@@ -327,7 +327,7 @@
{
int error, call_nests = 0;
unsigned long flags;
- struct task_struct *this_task = current;
+ int this_cpu = get_cpu();
struct list_head *lsthead = &ncalls->tasks_call_list;
struct nested_call_node *tncur;
struct nested_call_node tnode;
@@ -340,20 +340,19 @@
* very much limited.
*/
list_for_each_entry(tncur, lsthead, llink) {
- if (tncur->task == this_task &&
+ if (tncur->cpu == this_cpu &&
(tncur->cookie == cookie || ++call_nests > max_nests)) {
/*
* Ops ... loop detected or maximum nest level reached.
* We abort this wake by breaking the cycle itself.
*/
- spin_unlock_irqrestore(&ncalls->lock, flags);
-
- return -1;
+ error = -1;
+ goto out_unlock;
}
}
/* Add the current task and cookie to the list */
- tnode.task = this_task;
+ tnode.cpu = this_cpu;
tnode.cookie = cookie;
list_add(&tnode.llink, lsthead);
@@ -365,8 +364,10 @@
/* Remove the current task from the list */
spin_lock_irqsave(&ncalls->lock, flags);
list_del(&tnode.llink);
+ out_unlock:
spin_unlock_irqrestore(&ncalls->lock, flags);
+ put_cpu();
return error;
}