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SubjectRe: [PATCH V2] lglock: add read-preference local-global rwlock
On 03/03/13 01:11, Srivatsa S. Bhat wrote:
> On 03/02/2013 06:44 PM, Lai Jiangshan wrote:
>> From 345a7a75c314ff567be48983e0892bc69c4452e7 Mon Sep 17 00:00:00 2001
>> From: Lai Jiangshan <laijs@cn.fujitsu.com>
>> Date: Sat, 2 Mar 2013 20:33:14 +0800
>> Subject: [PATCH] lglock: add read-preference local-global rwlock
>>
>> Current lglock is not read-preference, so it can't be used on some cases
>> which read-preference rwlock can do. Example, get_cpu_online_atomic().
>>
> [...]
>> diff --git a/kernel/lglock.c b/kernel/lglock.c
>> index 6535a66..52e9b2c 100644
>> --- a/kernel/lglock.c
>> +++ b/kernel/lglock.c
>> @@ -87,3 +87,71 @@ void lg_global_unlock(struct lglock *lg)
>> preempt_enable();
>> }
>> EXPORT_SYMBOL(lg_global_unlock);
>> +
>> +#define FALLBACK_BASE (1UL << 30)
>> +
>> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
>> +{
>> + struct lglock *lg = &lgrw->lglock;
>> +
>> + preempt_disable();
>> + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) {
>> + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_);
>> + if (unlikely(!arch_spin_trylock(this_cpu_ptr(lg->lock)))) {
>> + read_lock(&lgrw->fallback_rwlock);
>> + __this_cpu_write(*lgrw->reader_refcnt, FALLBACK_BASE);
>> + return;
>> + }
>> + }
>> +
>> + __this_cpu_inc(*lgrw->reader_refcnt);
>> +}
>> +EXPORT_SYMBOL(lg_rwlock_local_read_lock);
>> +
>> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
>> +{
>> + switch (__this_cpu_read(*lgrw->reader_refcnt)) {
>> + case 1:
>> + __this_cpu_write(*lgrw->reader_refcnt, 0);
>> + lg_local_unlock(&lgrw->lglock);
>> + return;
>
> This should be a break, instead of a return, right?
> Otherwise, there will be a preempt imbalance...


"lockdep" and "preempt" are handled in lg_local_unlock(&lgrw->lglock);

Thanks,
Lai

>
>> + case FALLBACK_BASE:
>> + __this_cpu_write(*lgrw->reader_refcnt, 0);
>> + read_unlock(&lgrw->fallback_rwlock);
>> + rwlock_release(&lg->lock_dep_map, 1, _RET_IP_);
>> + break;
>> + default:
>> + __this_cpu_dec(*lgrw->reader_refcnt);
>> + break;
>> + }
>> +
>> + preempt_enable();
>> +}
>
>
> Regards,
> Srivatsa S. Bhat
>
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