From: Kent Overstreet <kent.overstreet@linux.dev>
Date: Mon, 24 Mar 2025 15:51:01 +0000 (-0400)
Subject: bcachefs: Fix silent short reads in data read retry path
X-Git-Tag: v6.15-rc1~83^2~33
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3ba0240a8789;p=thirdparty%2Flinux.git

bcachefs: Fix silent short reads in data read retry path

__bch2_read, before calling __bch2_read_extent(), sets bvec_iter.bi_size
to "the size we can read from the current extent" with a swap, and
restores it to "the size for the total read" after the read_extent call
with another swap.

But we neglected to do the restore before the "if (ret) goto err;" -
which is a problem if we're retrying those errors.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---

diff --git a/fs/bcachefs/fs-io-buffered.c b/fs/bcachefs/fs-io-buffered.c
index 5ab1c73c8d4c9..a03e2c780cba0 100644
--- a/fs/bcachefs/fs-io-buffered.c
+++ b/fs/bcachefs/fs-io-buffered.c
@@ -225,11 +225,11 @@ static void bchfs_read(struct btree_trans *trans,
 
 		bch2_read_extent(trans, rbio, iter.pos,
 				 data_btree, k, offset_into_extent, flags);
+		swap(rbio->bio.bi_iter.bi_size, bytes);
 
 		if (flags & BCH_READ_last_fragment)
 			break;
 
-		swap(rbio->bio.bi_iter.bi_size, bytes);
 		bio_advance(&rbio->bio, bytes);
 err:
 		if (ret &&
diff --git a/fs/bcachefs/io_read.c b/fs/bcachefs/io_read.c
index f1503df57dc71..fafd00a3d6c95 100644
--- a/fs/bcachefs/io_read.c
+++ b/fs/bcachefs/io_read.c
@@ -1322,13 +1322,14 @@ int __bch2_read(struct btree_trans *trans, struct bch_read_bio *rbio,
 		ret = __bch2_read_extent(trans, rbio, bvec_iter, iter.pos,
 					 data_btree, k,
 					 offset_into_extent, failed, flags, -1);
+		swap(bvec_iter.bi_size, bytes);
+
 		if (ret)
 			goto err;
 
 		if (flags & BCH_READ_last_fragment)
 			break;
 
-		swap(bvec_iter.bi_size, bytes);
 		bio_advance_iter(&rbio->bio, &bvec_iter, bytes);
 err:
 		if (ret == -BCH_ERR_data_read_retry_csum_err_maybe_userspace)
diff --git a/fs/bcachefs/io_read.h b/fs/bcachefs/io_read.h
index cd21950417f64..c78025d863e0f 100644
--- a/fs/bcachefs/io_read.h
+++ b/fs/bcachefs/io_read.h
@@ -137,8 +137,10 @@ static inline void bch2_read_extent(struct btree_trans *trans,
 			enum btree_id data_btree, struct bkey_s_c k,
 			unsigned offset_into_extent, unsigned flags)
 {
-	__bch2_read_extent(trans, rbio, rbio->bio.bi_iter, read_pos,
-			   data_btree, k, offset_into_extent, NULL, flags, -1);
+	int ret = __bch2_read_extent(trans, rbio, rbio->bio.bi_iter, read_pos,
+				     data_btree, k, offset_into_extent, NULL, flags, -1);
+	/* __bch2_read_extent only returns errors if BCH_READ_in_retry is set */
+	WARN(ret, "unhandled error from __bch2_read_extent()");
 }
 
 int __bch2_read(struct btree_trans *, struct bch_read_bio *, struct bvec_iter,