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Message-ID: <6f2084ae-61d5-8cb9-c975-901456eed7e3@gmail.com>
Date: Fri, 14 Jun 2019 15:06:10 +0200
From: Christian König <ckoenig.leichtzumerken@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: daniel@...ll.ch, l.stach@...gutronix.de,
linux+etnaviv@...linux.org.uk, christian.gmeiner@...il.com,
yuq825@...il.com, eric@...olt.net, thellstrom@...are.com,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
etnaviv@...ts.freedesktop.org, lima@...ts.freedesktop.org
Subject: Re: [PATCH 3/6] drm/gem: use new ww_mutex_(un)lock_for_each macros
Am 14.06.19 um 14:59 schrieb Peter Zijlstra:
> On Fri, Jun 14, 2019 at 02:41:22PM +0200, Christian König wrote:
>> Use the provided macros instead of implementing deadlock handling on our own.
>>
>> Signed-off-by: Christian König <christian.koenig@....com>
>> ---
>> drivers/gpu/drm/drm_gem.c | 49 ++++++++++-----------------------------
>> 1 file changed, 12 insertions(+), 37 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> index 50de138c89e0..6e4623d3bee2 100644
>> --- a/drivers/gpu/drm/drm_gem.c
>> +++ b/drivers/gpu/drm/drm_gem.c
>> @@ -1307,51 +1307,26 @@ int
>> drm_gem_lock_reservations(struct drm_gem_object **objs, int count,
>> struct ww_acquire_ctx *acquire_ctx)
>> {
>> - int contended = -1;
>> + struct ww_mutex *contended;
>> int i, ret;
>>
>> ww_acquire_init(acquire_ctx, &reservation_ww_class);
>>
>> -retry:
>> - if (contended != -1) {
>> - struct drm_gem_object *obj = objs[contended];
>> -
>> - ret = ww_mutex_lock_slow_interruptible(&obj->resv->lock,
>> - acquire_ctx);
>> - if (ret) {
>> - ww_acquire_done(acquire_ctx);
>> - return ret;
>> - }
>> - }
>> -
>> - for (i = 0; i < count; i++) {
>> - if (i == contended)
>> - continue;
>> -
>> - ret = ww_mutex_lock_interruptible(&objs[i]->resv->lock,
>> - acquire_ctx);
>> - if (ret) {
>> - int j;
>> -
>> - for (j = 0; j < i; j++)
>> - ww_mutex_unlock(&objs[j]->resv->lock);
>> -
>> - if (contended != -1 && contended >= i)
>> - ww_mutex_unlock(&objs[contended]->resv->lock);
>> -
>> - if (ret == -EDEADLK) {
>> - contended = i;
>> - goto retry;
> retry here, starts the whole locking loop.
>
>> - }
>> -
>> - ww_acquire_done(acquire_ctx);
>> - return ret;
>> - }
>> - }
> +#define ww_mutex_unlock_for_each(loop, pos, contended) \
> + if (!IS_ERR(contended)) { \
> + if (contended) \
> + ww_mutex_unlock(contended); \
> + contended = (pos); \
> + loop { \
> + if (contended == (pos)) \
> + break; \
> + ww_mutex_unlock(pos); \
> + } \
> + }
> +
>
> +#define ww_mutex_lock_for_each(loop, pos, contended, ret, intr, ctx) \
> + for (contended = ERR_PTR(-ENOENT); ({ \
> + __label__ relock, next; \
> + ret = -ENOENT; \
> + if (contended == ERR_PTR(-ENOENT)) \
> + contended = NULL; \
> + else if (contended == ERR_PTR(-EDEADLK)) \
> + contended = (pos); \
> + else \
> + goto next; \
> + loop { \
> + if (contended == (pos)) { \
> + contended = NULL; \
> + continue; \
> + } \
> +relock: \
> + ret = !(intr) ? ww_mutex_lock(pos, ctx) : \
> + ww_mutex_lock_interruptible(pos, ctx); \
> + if (ret == -EDEADLK) { \
> + ww_mutex_unlock_for_each(loop, pos, \
> + contended); \
> + contended = ERR_PTR(-EDEADLK); \
> + goto relock; \
>
> while relock here continues where it left of and doesn't restart @loop.
> Or am I reading this monstrosity the wrong way?
contended = ERR_PTR(-EDEADLK) makes sure that the whole loop is
restarted after retrying to acquire the lock.
See the "if" above "loop".
Christian.
>
> + } \
> + break; \
> +next: \
> + continue; \
> + } \
> + }), ret != -ENOENT;)
> +
>
>> + ww_mutex_lock_for_each(for (i = 0; i < count; i++),
>> + &objs[i]->resv->lock, contended, ret, true,
>> + acquire_ctx)
>> + if (ret)
>> + goto error;
>>
>> ww_acquire_done(acquire_ctx);
>>
>> return 0;
>> +
>> +error:
>> + ww_mutex_unlock_for_each(for (i = 0; i < count; i++),
>> + &objs[i]->resv->lock, contended);
>> + ww_acquire_done(acquire_ctx);
>> + return ret;
>> }
>> EXPORT_SYMBOL(drm_gem_lock_reservations);
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