[PATCH v2 3/8] fs/buffer: introduce __find_get_block_nonatomic()

[Luis Chamberlain <mcgrof@xxxxxxxxxx>]

From: Davidlohr Bueso <dave@xxxxxxxxxxxx>

Callers that do not require atomic context for pagecache
lookups can use this flavor to avoid the unnencesary
contention on the blockdev mapping i_private_lock as well
as waiting on noref migration.

Convert local caller write_boundary_block() which already
takes the buffer lock as well as bdev_getblk() depending
on the respective gpf flags. Either way there are no
currently changes in semantics.

Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
 fs/buffer.c                 | 19 +++++++++++++++++--
 include/linux/buffer_head.h |  2 ++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 5a1a37a6840a..07ec57ec100e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -662,7 +662,8 @@ EXPORT_SYMBOL(generic_buffers_fsync);
 void write_boundary_block(struct block_device *bdev,
 			sector_t bblock, unsigned blocksize)
 {
-	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
+	struct buffer_head *bh = __find_get_block_nonatomic(bdev, bblock + 1,
+							    blocksize);
 	if (bh) {
 		if (buffer_dirty(bh))
 			write_dirty_buffer(bh, 0);
@@ -1418,6 +1419,15 @@ __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
 }
 EXPORT_SYMBOL(__find_get_block);
 
+/* same as __find_get_block() but allows sleeping contexts */
+struct buffer_head *
+__find_get_block_nonatomic(struct block_device *bdev, sector_t block,
+			   unsigned size)
+{
+	return find_get_block_common(bdev, block, size, false);
+}
+EXPORT_SYMBOL(__find_get_block_nonatomic);
+
 /**
  * bdev_getblk - Get a buffer_head in a block device's buffer cache.
  * @bdev: The block device.
@@ -1435,7 +1445,12 @@ EXPORT_SYMBOL(__find_get_block);
 struct buffer_head *bdev_getblk(struct block_device *bdev, sector_t block,
 		unsigned size, gfp_t gfp)
 {
-	struct buffer_head *bh = __find_get_block(bdev, block, size);
+	struct buffer_head *bh;
+
+	if (gfpflags_allow_blocking(gfp))
+		bh = __find_get_block_nonatomic(bdev, block, size);
+	else
+		bh = __find_get_block(bdev, block, size);
 
 	might_alloc(gfp);
 	if (bh)
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index f0a4ad7839b6..2b5458517def 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -222,6 +222,8 @@ void __wait_on_buffer(struct buffer_head *);
 wait_queue_head_t *bh_waitq_head(struct buffer_head *bh);
 struct buffer_head *__find_get_block(struct block_device *bdev, sector_t block,
 			unsigned size);
+struct buffer_head *__find_get_block_nonatomic(struct block_device *bdev,
+		       sector_t block, unsigned size);
 struct buffer_head *bdev_getblk(struct block_device *bdev, sector_t block,
 		unsigned size, gfp_t gfp);
 void __brelse(struct buffer_head *);
-- 
2.47.2