[PATCH 6.18.y 2/2] iomap: don't lose a failed direct I/O bio's error when zeroing the tail

[Sasha Levin <sashal@kernel.org>]

From: Andrea Parri <parri.andrea@gmail.com>

[ Upstream commit a9fd24bcbe690ed4a5b8ea6a7516fa297fae9360 ]

iomap_dio_bio_iter() falls through to the sub-block tail zeroing when
the data bio submission fails, so that the rest of the block is still
zeroed and stale data is not exposed.  The zeroing result was assigned
to ret, which overwrote the submission error with the successful
zeroing result (zero) and the failed write was reported as success.

iomap_dio_zero() can only return an error from a can't-happen
WARN_ON_ONCE() (nr_vecs exceeding BIO_MAX_VECS, which the existing
comment there says "shall never be reached" for any in-tree
filesystem), so it isn't a real runtime failure worth reporting to
userspace, let alone one worth losing the actual submission error for.
Make iomap_dio_zero() return void and drop the error handling at both
call sites instead of threading the result through a separate
variable.

Fixes: 10553a91652d ("iomap: fix iomap_dio_zero() for fs bs > system page size")
Cc: stable@vger.kernel.org # v6.12
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://patch.msgid.link/0cbce1012f5333690be36a9adafb3e190fe2ca77.1790342457.git.parri.andrea@gmail.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/iomap/direct-io.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 5a97614507530..4301145674259 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -284,7 +284,7 @@ u32 iomap_finish_ioend_direct(struct iomap_ioend *ioend)
 	return vec_count;
 }
 
-static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
+static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		loff_t pos, unsigned len)
 {
 	struct inode *inode = file_inode(dio->iocb->ki_filp);
@@ -293,14 +293,14 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 	int nr_vecs = max(1, i_blocksize(inode) / folio_size(zero_folio));
 
 	if (!len)
-		return 0;
+		return;
 
 	/*
 	 * This limit shall never be reached as most filesystems have a
 	 * maximum blocksize of 64k.
 	 */
 	if (WARN_ON_ONCE(nr_vecs > BIO_MAX_VECS))
-		return -EINVAL;
+		return;
 
 	bio = iomap_dio_alloc_bio(iter, dio, nr_vecs,
 				  REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
@@ -317,8 +317,6 @@ static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
 		len -= io_len;
 	}
 	iomap_dio_submit_bio(iter, dio, bio, pos);
-
-	return 0;
 }
 
 /*
@@ -424,10 +422,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
 		pad = pos & (fs_block_size - 1);
-
-		ret = iomap_dio_zero(iter, dio, pos - pad, pad);
-		if (ret)
-			goto out;
+		iomap_dio_zero(iter, dio, pos - pad, pad);
 	}
 
 	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
@@ -509,8 +504,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 		/* zero out from the end of the write to the end of the block */
 		pad = pos & (fs_block_size - 1);
 		if (pad)
-			ret = iomap_dio_zero(iter, dio, pos,
-					     fs_block_size - pad);
+			iomap_dio_zero(iter, dio, pos, fs_block_size - pad);
 	}
 out:
 	/* Undo iter limitation to current extent */
-- 
2.53.0