[PATCH 4/6] fs: Hoist fscrypt decryption to bio completion handler

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

This is prep work for doing decryption at the BIO level instead of
the BH level.  It still works on one BH at a time for now.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/buffer.c | 45 +++++++++++++++++++++------------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index ccb90081117c..627ae1d853c0 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -241,6 +241,10 @@ __find_get_block_slow(struct block_device *bdev, sector_t block)
 	return ret;
 }
 
+/*
+ * I/O completion handler for block_read_full_page() - pages
+ * which come unlocked at the end of I/O.
+ */
 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 {
 	unsigned long flags;
@@ -313,28 +317,6 @@ static void decrypt_bh(struct work_struct *work)
 	kfree(ctx);
 }
 
-/*
- * I/O completion handler for block_read_full_page() - pages
- * which come unlocked at the end of I/O.
- */
-static void end_buffer_async_read_io(struct buffer_head *bh, int uptodate)
-{
-	/* Decrypt if needed */
-	if (uptodate &&
-	    fscrypt_inode_uses_fs_layer_crypto(bh->b_page->mapping->host)) {
-		struct decrypt_bh_ctx *ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
-
-		if (ctx) {
-			INIT_WORK(&ctx->work, decrypt_bh);
-			ctx->bh = bh;
-			fscrypt_enqueue_decrypt_work(&ctx->work);
-			return;
-		}
-		uptodate = 0;
-	}
-	end_buffer_async_read(bh, uptodate);
-}
-
 /*
  * Completion handler for block_write_full_page() - pages which are unlocked
  * during I/O, and which have PageWriteback cleared upon I/O completion.
@@ -404,7 +386,7 @@ EXPORT_SYMBOL(end_buffer_async_write);
  */
 static void mark_buffer_async_read(struct buffer_head *bh)
 {
-	bh->b_end_io = end_buffer_async_read_io;
+	bh->b_end_io = end_buffer_async_read;
 	set_buffer_async_read(bh);
 }
 
@@ -3103,11 +3085,26 @@ EXPORT_SYMBOL(generic_block_bmap);
 static void end_bio_bh_io_sync(struct bio *bio)
 {
 	struct buffer_head *bh = bio->bi_private;
+	int uptodate = !bio->bi_status;
 
 	if (unlikely(bio_flagged(bio, BIO_QUIET)))
 		set_bit(BH_Quiet, &bh->b_state);
 
-	bh->b_end_io(bh, !bio->bi_status);
+	/* Decrypt if needed */
+	if ((bio_data_dir(bio) == READ) && uptodate &&
+	    fscrypt_inode_uses_fs_layer_crypto(bh->b_page->mapping->host)) {
+		struct decrypt_bh_ctx *ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
+
+		if (ctx) {
+			INIT_WORK(&ctx->work, decrypt_bh);
+			ctx->bh = bh;
+			fscrypt_enqueue_decrypt_work(&ctx->work);
+			bio_put(bio);
+			return;
+		}
+		uptodate = 0;
+	}
+	bh->b_end_io(bh, uptodate);
 	bio_put(bio);
 }
 
-- 
2.28.0