drm/ttm: introduce pool_shrink_rwsem

Currently, synchronize_shrinkers() is only used by TTM pool.  It only
requires that no shrinkers run in parallel.

After we use RCU+refcount method to implement the lockless slab shrink, we
can not use shrinker_rwsem or synchronize_rcu() to guarantee that all
shrinker invocations have seen an update before freeing memory.

So we introduce a new pool_shrink_rwsem to implement a private
ttm_pool_synchronize_shrinkers(), so as to achieve the same purpose.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Qi Zheng <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Reviewed-by: Christian König <[email protected]>
Acked-by: Daniel Vetter <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Chuck Lever <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Kirill Tkhai <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Steven Price <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Abhinav Kumar <[email protected]>
Cc: Alasdair Kergon <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Alyssa Rosenzweig <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Andreas Gruenbacher <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Bob Peterson <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Carlos Llamas <[email protected]>
Cc: Chandan Babu R <[email protected]>
Cc: Chao Yu <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Coly Li <[email protected]>
Cc: Dai Ngo <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Airlie <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Sterba <[email protected]>
Cc: Dmitry Baryshkov <[email protected]>
Cc: Gao Xiang <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jaegeuk Kim <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: Jeffle Xu <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Marijn Suijten <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Mike Snitzer <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Neil Brown <[email protected]>
Cc: Oleksandr Tyshchenko <[email protected]>
Cc: Olga Kornievskaia <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Rob Clark <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Cc: Sean Paul <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tomeu Vizoso <[email protected]>
Cc: Tom Talpey <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Cc: Yue Hu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index cddb9151d20f..648ca70403a7 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -74,6 +74,7 @@ static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
 static spinlock_t shrinker_lock;
 static struct list_head shrinker_list;
 static struct shrinker mm_shrinker;
+static DECLARE_RWSEM(pool_shrink_rwsem);
 
 /* Allocate pages of size 1 << order with the given gfp_flags */
 static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
@@ -317,6 +318,7 @@ static unsigned int ttm_pool_shrink(void)
 	unsigned int num_pages;
 	struct page *p;
 
+	down_read(&pool_shrink_rwsem);
 	spin_lock(&shrinker_lock);
 	pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
 	list_move_tail(&pt->shrinker_list, &shrinker_list);
@@ -329,6 +331,7 @@ static unsigned int ttm_pool_shrink(void)
 	} else {
 		num_pages = 0;
 	}
+	up_read(&pool_shrink_rwsem);
 
 	return num_pages;
 }
@@ -573,6 +576,18 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
 EXPORT_SYMBOL(ttm_pool_init);
 
 /**
+ * ttm_pool_synchronize_shrinkers - Wait for all running shrinkers to complete.
+ *
+ * This is useful to guarantee that all shrinker invocations have seen an
+ * update, before freeing memory, similar to rcu.
+ */
+static void ttm_pool_synchronize_shrinkers(void)
+{
+	down_write(&pool_shrink_rwsem);
+	up_write(&pool_shrink_rwsem);
+}
+
+/**
  * ttm_pool_fini - Cleanup a pool
  *
  * @pool: the pool to clean up
@@ -593,7 +608,7 @@ void ttm_pool_fini(struct ttm_pool *pool)
 	/* We removed the pool types from the LRU, but we need to also make sure
 	 * that no shrinker is concurrently freeing pages from the pool.
 	 */
-	synchronize_shrinkers();
+	ttm_pool_synchronize_shrinkers();
 }
 EXPORT_SYMBOL(ttm_pool_fini);