[PATCH] drm/ttm: make the pool shrinker lock a mutex

[Christian König]

Am 12.01.21 um 15:03 schrieb Daniel Vetter:
> On Mon, Jan 11, 2021 at 2:57 PM Christian König
> <ckoenig.leichtzumerken at gmail.com> wrote:
>> set_pages_wb() might sleep and so we can't do this in an atomic context.
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
>> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov at gmail.com>
>> Fixes: d099fc8f540a ("drm/ttm: new TT backend allocation pool v3")
> Hm I guess long term proper fix would be to pull the shrinker into two
> parts, first part takes the right amount of entries of the list,
> holding the lock. 2nd part does the releasing (or maybe at least in
> batches). lru locks should be cheap, doing expensive stuff like
> flushing or rewriting ptes might not be the best idea.

Yeah, agree. It should actually be trivial, but I didn't wanted the 
churn in fixes.

So just going for the easy fix now and the optimal later on.

Regards,
Christian.

> -Daniel
>
>> ---
>>   drivers/gpu/drm/ttm/ttm_pool.c | 20 ++++++++++----------
>>   1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
>> index a00b7ab9c14c..6a6eeba423d1 100644
>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>> @@ -66,7 +66,7 @@ static struct ttm_pool_type global_uncached[MAX_ORDER];
>>   static struct ttm_pool_type global_dma32_write_combined[MAX_ORDER];
>>   static struct ttm_pool_type global_dma32_uncached[MAX_ORDER];
>>
>> -static spinlock_t shrinker_lock;
>> +static struct mutex shrinker_lock;
>>   static struct list_head shrinker_list;
>>   static struct shrinker mm_shrinker;
>>
>> @@ -249,9 +249,9 @@ static void ttm_pool_type_init(struct ttm_pool_type *pt, struct ttm_pool *pool,
>>          spin_lock_init(&pt->lock);
>>          INIT_LIST_HEAD(&pt->pages);
>>
>> -       spin_lock(&shrinker_lock);
>> +       mutex_lock(&shrinker_lock);
>>          list_add_tail(&pt->shrinker_list, &shrinker_list);
>> -       spin_unlock(&shrinker_lock);
>> +       mutex_unlock(&shrinker_lock);
>>   }
>>
>>   /* Remove a pool_type from the global shrinker list and free all pages */
>> @@ -259,9 +259,9 @@ static void ttm_pool_type_fini(struct ttm_pool_type *pt)
>>   {
>>          struct page *p, *tmp;
>>
>> -       spin_lock(&shrinker_lock);
>> +       mutex_lock(&shrinker_lock);
>>          list_del(&pt->shrinker_list);
>> -       spin_unlock(&shrinker_lock);
>> +       mutex_unlock(&shrinker_lock);
>>
>>          list_for_each_entry_safe(p, tmp, &pt->pages, lru)
>>                  ttm_pool_free_page(pt->pool, pt->caching, pt->order, p);
>> @@ -302,7 +302,7 @@ static unsigned int ttm_pool_shrink(void)
>>          unsigned int num_freed;
>>          struct page *p;
>>
>> -       spin_lock(&shrinker_lock);
>> +       mutex_lock(&shrinker_lock);
>>          pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
>>
>>          p = ttm_pool_type_take(pt);
>> @@ -314,7 +314,7 @@ static unsigned int ttm_pool_shrink(void)
>>          }
>>
>>          list_move_tail(&pt->shrinker_list, &shrinker_list);
>> -       spin_unlock(&shrinker_lock);
>> +       mutex_unlock(&shrinker_lock);
>>
>>          return num_freed;
>>   }
>> @@ -564,7 +564,7 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
>>   {
>>          unsigned int i;
>>
>> -       spin_lock(&shrinker_lock);
>> +       mutex_lock(&shrinker_lock);
>>
>>          seq_puts(m, "\t ");
>>          for (i = 0; i < MAX_ORDER; ++i)
>> @@ -600,7 +600,7 @@ int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)
>>          seq_printf(m, "\ntotal\t: %8lu of %8lu\n",
>>                     atomic_long_read(&allocated_pages), page_pool_size);
>>
>> -       spin_unlock(&shrinker_lock);
>> +       mutex_unlock(&shrinker_lock);
>>
>>          return 0;
>>   }
>> @@ -644,7 +644,7 @@ int ttm_pool_mgr_init(unsigned long num_pages)
>>          if (!page_pool_size)
>>                  page_pool_size = num_pages;
>>
>> -       spin_lock_init(&shrinker_lock);
>> +       mutex_init(&shrinker_lock);
>>          INIT_LIST_HEAD(&shrinker_list);
>>
>>          for (i = 0; i < MAX_ORDER; ++i) {
>> --
>> 2.25.1
>>
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>
>