tasklets: new tasklet scheduling function

Rationale: kmemcheck needs to be able to schedule a tasklet without
touching any dynamically allocated memory _at_ _all_ (since that would
lead to a recursive page fault). This tasklet is used for writing the
error reports to the kernel log.

The new scheduling function avoids touching any other tasklets by
inserting the new tasklist as the head of the "tasklet_hi" list instead
of on the tail.

Also don't wake up the softirq thread lest the scheduler access some
tracked memory and we go down with a recursive page fault.

In this case, we'd better just wait for the maximum time of 1/HZ for the
message to appear.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 258885a543d..b41fb710e11 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -382,6 +382,17 @@ void __tasklet_hi_schedule(struct tasklet_struct *t)
 
 EXPORT_SYMBOL(__tasklet_hi_schedule);
 
+void __tasklet_hi_schedule_first(struct tasklet_struct *t)
+{
+	BUG_ON(!irqs_disabled());
+
+	t->next = __get_cpu_var(tasklet_hi_vec).head;
+	__get_cpu_var(tasklet_hi_vec).head = t;
+	__raise_softirq_irqoff(HI_SOFTIRQ);
+}
+
+EXPORT_SYMBOL(__tasklet_hi_schedule_first);
+
 static void tasklet_action(struct softirq_action *a)
 {
 	struct tasklet_struct *list;