linux-kernel - [PATCH] fs/buffer: use min folio order to calculate upper limit in __getblk

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Message-ID: <20250618091710.119946-1-p.raghav@samsung.com>
Date: Wed, 18 Jun 2025 11:17:10 +0200
From: Pankaj Raghav <p.raghav@...sung.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
	Jan Kara <jack@...e.cz>,
	mcgrof@...nel.org,
	Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	gost.dev@...sung.com,
	kernel@...kajraghav.com,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [PATCH] fs/buffer: use min folio order to calculate upper limit in __getblk_slow()

The maximum IO size that a block device can read as a single block is
based on the min folio order and not the PAGE_SIZE as we have bs > ps
support for block devices[1].

Calculate the upper limit based on the on min folio order.

[1] https://lore.kernel.org/linux-block/20250221223823.1680616-1-mcgrof@kernel.org/

Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
I found this while I was adding bs > ps support to ext4. Ext4 uses this
routine to read the superblock.

 fs/buffer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 8cf4a1dc481e..98f90da69a0a 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1121,10 +1121,11 @@ __getblk_slow(struct block_device *bdev, sector_t block,
 	     unsigned size, gfp_t gfp)
 {
 	bool blocking = gfpflags_allow_blocking(gfp);
+	int blocklog = PAGE_SHIFT + mapping_min_folio_order(bdev->bd_mapping);
 
 	/* Size must be multiple of hard sectorsize */
-	if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
-			(size < 512 || size > PAGE_SIZE))) {
+	if (unlikely(size & (bdev_logical_block_size(bdev) - 1) ||
+		     (size < 512 || size > (1U << blocklog)))) {
 		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
 					size);
 		printk(KERN_ERR "logical block size: %d\n",

base-commit: e04c78d86a9699d136910cfc0bdcf01087e3267e
-- 
2.49.0