[PATCH 2/4] brd: check for REQ_NOWAIT and set correct page allocation mask

[Jens Axboe <axboe@kernel.dk>]

If REQ_NOWAIT is set, then do a non-blocking allocation if the operation
is a write and we need to insert a new page. Currently REQ_NOWAIT cannot
be set as the queue isn't marked as supporting nowait, this change is in
preparation for allowing that.

Cc: stable@vger.kernel.org # 5.10+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 drivers/block/brd.c | 39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 15a148d5aad9..1ddada0cdaca 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -80,26 +80,20 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
 /*
  * Insert a new page for a given sector, if one does not already exist.
  */
-static int brd_insert_page(struct brd_device *brd, sector_t sector)
+static int brd_insert_page(struct brd_device *brd, sector_t sector, gfp_t gfp)
 {
 	pgoff_t idx;
 	struct page *page;
-	gfp_t gfp_flags;
 
 	page = brd_lookup_page(brd, sector);
 	if (page)
 		return 0;
 
-	/*
-	 * Must use NOIO because we don't want to recurse back into the
-	 * block or filesystem layers from page reclaim.
-	 */
-	gfp_flags = GFP_NOIO | __GFP_ZERO | __GFP_HIGHMEM;
-	page = alloc_page(gfp_flags);
+	page = alloc_page(gfp | __GFP_ZERO | __GFP_HIGHMEM);
 	if (!page)
 		return -ENOMEM;
 
-	if (radix_tree_preload(GFP_NOIO)) {
+	if (radix_tree_preload(gfp)) {
 		__free_page(page);
 		return -ENOMEM;
 	}
@@ -167,19 +161,20 @@ static void brd_free_pages(struct brd_device *brd)
 /*
  * copy_to_brd_setup must be called before copy_to_brd. It may sleep.
  */
-static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n)
+static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n,
+			     gfp_t gfp)
 {
 	unsigned int offset = (sector & (PAGE_SECTORS-1)) << SECTOR_SHIFT;
 	size_t copy;
 	int ret;
 
 	copy = min_t(size_t, n, PAGE_SIZE - offset);
-	ret = brd_insert_page(brd, sector);
+	ret = brd_insert_page(brd, sector, gfp);
 	if (ret)
 		return ret;
 	if (copy < n) {
 		sector += copy >> SECTOR_SHIFT;
-		ret = brd_insert_page(brd, sector);
+		ret = brd_insert_page(brd, sector, gfp);
 	}
 	return ret;
 }
@@ -254,20 +249,26 @@ static void copy_from_brd(void *dst, struct brd_device *brd,
  * Process a single bvec of a bio.
  */
 static int brd_do_bvec(struct brd_device *brd, struct page *page,
-			unsigned int len, unsigned int off, enum req_op op,
+			unsigned int len, unsigned int off, blk_opf_t opf,
 			sector_t sector)
 {
 	void *mem;
 	int err = 0;
 
-	if (op_is_write(op)) {
-		err = copy_to_brd_setup(brd, sector, len);
+	if (op_is_write(opf)) {
+		/*
+		 * Must use NOIO because we don't want to recurse back into the
+		 * block or filesystem layers from page reclaim.
+		 */
+		gfp_t gfp = opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO;
+
+		err = copy_to_brd_setup(brd, sector, len, gfp);
 		if (err)
 			goto out;
 	}
 
 	mem = kmap_atomic(page);
-	if (!op_is_write(op)) {
+	if (!op_is_write(opf)) {
 		copy_from_brd(mem + off, brd, sector, len);
 		flush_dcache_page(page);
 	} else {
@@ -296,8 +297,12 @@ static void brd_submit_bio(struct bio *bio)
 				(len & (SECTOR_SIZE - 1)));
 
 		err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
-				  bio_op(bio), sector);
+				  bio->bi_opf, sector);
 		if (err) {
+			if (err == -ENOMEM && bio->bi_opf & REQ_NOWAIT) {
+				bio_wouldblock_error(bio);
+				return;
+			}
 			bio_io_error(bio);
 			return;
 		}
-- 
2.39.1