Subject: Re: [PATCH v2 3/3] sched/preempt: fix cond_resched_lock() and cond_resched_softirq()

From: Konstantin Khlebnikov <[email-masked]>
Date: Wed, 15 Jul 2015 15:52:34 +0300

On 15.07.2015 15:16, Eric Dumazet wrote:
> On Wed, 2015-07-15 at 12:52 +0300, Konstantin Khlebnikov wrote:
>> These functions check should_resched() before unlocking spinlock/bh-enable:
>> preempt_count always non-zero => should_resched() always returns false.
>> cond_resched_lock() worked iff spin_needbreak is set.
>
> Interesting, this definitely used to work (linux-3.11)
>
> Any idea of which commit broke things ?
>

Searching... done

This one: bdb43806589096ac4272fe1307e789846ac08d7c in v3.13

before

-static inline int should_resched(void)
-{
-       return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
-}

after

+static __always_inline bool should_resched(void)
+{
+       return unlikely(!*preempt_count_ptr());
+}

So,

Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count 
modifiers")

-- 
Konstantin