From 7c692cbade8b8884f1c20500393bcc7cd6d24ef8 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Wed, 21 May 2008 22:53:13 +0200 Subject: [PATCH] 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 --- include/linux/interrupt.h | 14 ++++++++++++++ kernel/softirq.c | 11 +++++++++++ 2 files changed, 25 insertions(+) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index ff374ce..dd574d5 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -466,6 +466,20 @@ static inline void tasklet_hi_schedule(struct tasklet_struct *t) __tasklet_hi_schedule(t); } +extern void __tasklet_hi_schedule_first(struct tasklet_struct *t); + +/* + * This version avoids touching any other tasklets. Needed for kmemcheck + * in order not to take any page faults while enqueueing this tasklet; + * consider VERY carefully whether you really need this or + * tasklet_hi_schedule()... + */ +static inline void tasklet_hi_schedule_first(struct tasklet_struct *t) +{ + if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) + __tasklet_hi_schedule_first(t); +} + static inline void tasklet_disable_nosync(struct tasklet_struct *t) { diff --git a/kernel/softirq.c b/kernel/softirq.c index 258885a..b41fb71 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; -- 2.7.4