fscrypt: stop using PG_error to track error status

As a step towards freeing the PG_error flag for other uses, change ext4
and f2fs to stop using PG_error to track decryption errors.  Instead, if
a decryption error occurs, just mark the whole bio as failed.  The
coarser granularity isn't really a problem since it isn't any worse than
what the block layer provides, and errors from a multi-page readahead
aren't reported to applications unless a single-page read fails too.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <chao@kernel.org> # for f2fs part
Link: https://lore.kernel.org/r/20220815235052.86545-2-ebiggers@kernel.org

fs/crypto/bio.c

@@ -25,21 +25,25 @@
  * then this function isn't applicable.  This function may sleep, so it must be
  * called from a workqueue rather than from the bio's bi_end_io callback.
  *
- * This function sets PG_error on any pages that contain any blocks that failed
- * to be decrypted.  The filesystem must not mark such pages uptodate.
+ * Return: %true on success; %false on failure.  On failure, bio->bi_status is
+ *	   also set to an error status.
  */
-void fscrypt_decrypt_bio(struct bio *bio)
+bool fscrypt_decrypt_bio(struct bio *bio)
 {
 	struct bio_vec *bv;
 	struct bvec_iter_all iter_all;
 
 	bio_for_each_segment_all(bv, bio, iter_all) {
 		struct page *page = bv->bv_page;
-		int ret = fscrypt_decrypt_pagecache_blocks(page, bv->bv_len,
+		int err = fscrypt_decrypt_pagecache_blocks(page, bv->bv_len,
 							   bv->bv_offset);
-		if (ret)
-			SetPageError(page);
+
+		if (err) {
+			bio->bi_status = errno_to_blk_status(err);
+			return false;
+		}
 	}
+	return true;
 }
 EXPORT_SYMBOL(fscrypt_decrypt_bio);
 

fs/ext4/readpage.c

@@ -75,7 +75,7 @@ static void __read_end_io(struct bio *bio)
 	bio_for_each_segment_all(bv, bio, iter_all) {
 		page = bv->bv_page;
 
-		/* PG_error was set if any post_read step failed */
+		/* PG_error was set if verity failed. */
 		if (bio->bi_status || PageError(page)) {
 			ClearPageUptodate(page);
 			/* will re-read again later */
@@ -96,10 +96,12 @@ static void decrypt_work(struct work_struct *work)
 {
 	struct bio_post_read_ctx *ctx =
 		container_of(work, struct bio_post_read_ctx, work);
+	struct bio *bio = ctx->bio;
 
-	fscrypt_decrypt_bio(ctx->bio);
-
-	bio_post_read_processing(ctx);
+	if (fscrypt_decrypt_bio(bio))
+		bio_post_read_processing(ctx);
+	else
+		__read_end_io(bio);
 }
 
 static void verity_work(struct work_struct *work)

fs/f2fs/data.c

@@ -139,7 +139,7 @@ static void f2fs_finish_read_bio(struct bio *bio, bool in_task)
 			continue;
 		}
 
-		/* PG_error was set if decryption or verity failed. */
+		/* PG_error was set if verity failed. */
 		if (bio->bi_status || PageError(page)) {
 			ClearPageUptodate(page);
 			/* will re-read again later */
@@ -185,7 +185,7 @@ static void f2fs_verify_bio(struct work_struct *work)
 			struct page *page = bv->bv_page;
 
 			if (!f2fs_is_compressed_page(page) &&
-			    !PageError(page) && !fsverity_verify_page(page))
+			    !fsverity_verify_page(page))
 				SetPageError(page);
 		}
 	} else {
@@ -236,10 +236,9 @@ static void f2fs_handle_step_decompress(struct bio_post_read_ctx *ctx,
 	bio_for_each_segment_all(bv, ctx->bio, iter_all) {
 		struct page *page = bv->bv_page;
 
-		/* PG_error was set if decryption failed. */
 		if (f2fs_is_compressed_page(page))
-			f2fs_end_read_compressed_page(page, PageError(page),
-						blkaddr, in_task);
+			f2fs_end_read_compressed_page(page, false, blkaddr,
+						      in_task);
 		else
 			all_compressed = false;
 
@@ -259,14 +258,17 @@ static void f2fs_post_read_work(struct work_struct *work)
 {
 	struct bio_post_read_ctx *ctx =
 		container_of(work, struct bio_post_read_ctx, work);
+	struct bio *bio = ctx->bio;
 
-	if (ctx->enabled_steps & STEP_DECRYPT)
-		fscrypt_decrypt_bio(ctx->bio);
+	if ((ctx->enabled_steps & STEP_DECRYPT) && !fscrypt_decrypt_bio(bio)) {
+		f2fs_finish_read_bio(bio, true);
+		return;
+	}
 
 	if (ctx->enabled_steps & STEP_DECOMPRESS)
 		f2fs_handle_step_decompress(ctx, true);
 
-	f2fs_verify_and_finish_bio(ctx->bio, true);
+	f2fs_verify_and_finish_bio(bio, true);
 }
 
 static void f2fs_read_end_io(struct bio *bio)

include/linux/fscrypt.h

@@ -351,7 +351,7 @@ u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name);
 int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags);
 
 /* bio.c */
-void fscrypt_decrypt_bio(struct bio *bio);
+bool fscrypt_decrypt_bio(struct bio *bio);
 int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
 			  sector_t pblk, unsigned int len);
 
@@ -644,8 +644,9 @@ static inline int fscrypt_d_revalidate(struct dentry *dentry,
 }
 
 /* bio.c */
-static inline void fscrypt_decrypt_bio(struct bio *bio)
+static inline bool fscrypt_decrypt_bio(struct bio *bio)
 {
+	return true;
 }
 
 static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,