linux-kernel - [PATCH -next v2 15/22] iomap: correct the range of a partial dirty clear

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Message-ID: <20260203062523.3869120-16-yi.zhang@huawei.com>
Date: Tue,  3 Feb 2026 14:25:15 +0800
From: Zhang Yi <yi.zhang@...wei.com>
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	jack@...e.cz,
	ojaswin@...ux.ibm.com,
	ritesh.list@...il.com,
	hch@...radead.org,
	djwong@...nel.org,
	yi.zhang@...wei.com,
	yi.zhang@...weicloud.com,
	yizhang089@...il.com,
	libaokun1@...wei.com,
	yangerkun@...wei.com,
	yukuai@...as.com
Subject: [PATCH -next v2 15/22] iomap: correct the range of a partial dirty clear

The block range calculation in ifs_clear_range_dirty() is incorrect when
partial clear a range in a folio. We can't clear the dirty bit of the
first block or the last block if the start or end offset is blocksize
unaligned, this has not yet caused any issue since we always clear a
whole folio in iomap_writeback_folio().

Fix this by round up the first block and round down the last block,
correct the calculation of nr_blks.

Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
---
This is modified from:
 https://lore.kernel.org/linux-fsdevel/20240812121159.3775074-2-yi.zhang@huaweicloud.com/
Changes:
 - Use round_up() instead of DIV_ROUND_UP() to prevent wasted integer
   division.

 fs/iomap/buffered-io.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 154456e39fe5..3c8e085e79cf 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -167,11 +167,15 @@ static void ifs_clear_range_dirty(struct folio *folio,
 {
 	struct inode *inode = folio->mapping->host;
 	unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
-	unsigned int first_blk = (off >> inode->i_blkbits);
-	unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
-	unsigned int nr_blks = last_blk - first_blk + 1;
+	unsigned int first_blk = round_up(off, i_blocksize(inode)) >>
+				 inode->i_blkbits;
+	unsigned int last_blk = (off + len) >> inode->i_blkbits;
+	unsigned int nr_blks = last_blk - first_blk;
 	unsigned long flags;
 
+	if (!nr_blks)
+		return;
+
 	spin_lock_irqsave(&ifs->state_lock, flags);
 	bitmap_clear(ifs->state, first_blk + blks_per_folio, nr_blks);
 	spin_unlock_irqrestore(&ifs->state_lock, flags);
-- 
2.52.0