+ fat-avoid-stack-overflow-warning.patch added to mm-hotfixes-unstable branch

+ fat-avoid-stack-overflow-warning.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: fat: avoid stack overflow warning
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     fat-avoid-stack-overflow-warning.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fat-avoid-stack-overflow-warning.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Arnd Bergmann <arnd@arndb.de>
Subject: fat: avoid stack overflow warning
Date: Fri, 15 May 2026 22:44:46 +0200

Building the fat kunit tests on with -fsanitize=alignment reveals some
rather excessive stack usage:

fs/fat/fat_test.c: In function 'fat_clus_to_blknr_test':
fs/fat/fat_test.c:33:1: error: the frame size of 4736 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
   33 | }
      | ^
fs/fat/fat_test.c: In function 'fat_get_blknr_offset_test':
fs/fat/fat_test.c:52:1: error: the frame size of 4800 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]

The problem is clearly related to the on-stack copy of a local
msdos_sb_info structure.  Avoid this by making that copy 'static const'
and changing the called functions to accept a constant input.

Link: https://lore.kernel.org/20260515204456.2692208-1-arnd@kernel.org
Fixes: 410002f8139c ("kunit: fat: test cluster and directory i_pos layout helpers")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Adi Nata <adinata.softwareengineer@gmail.com>
Cc: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/fat/fat.h      |    4 ++--
 fs/fat/fat_test.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/fs/fat/fat.h~fat-avoid-stack-overflow-warning
+++ a/fs/fat/fat.h
@@ -249,13 +249,13 @@ static inline unsigned char fat_checksum
 	return s;
 }
 
-static inline sector_t fat_clus_to_blknr(struct msdos_sb_info *sbi, int clus)
+static inline sector_t fat_clus_to_blknr(const struct msdos_sb_info *sbi, int clus)
 {
 	return ((sector_t)clus - FAT_START_ENT) * sbi->sec_per_clus
 		+ sbi->data_start;
 }
 
-static inline void fat_get_blknr_offset(struct msdos_sb_info *sbi,
+static inline void fat_get_blknr_offset(const struct msdos_sb_info *sbi,
 				loff_t i_pos, sector_t *blknr, int *offset)
 {
 	*blknr = i_pos >> sbi->dir_per_block_bits;
--- a/fs/fat/fat_test.c~fat-avoid-stack-overflow-warning
+++ a/fs/fat/fat_test.c
@@ -22,7 +22,7 @@ static void fat_checksum_test(struct kun
 
 static void fat_clus_to_blknr_test(struct kunit *test)
 {
-	struct msdos_sb_info sbi = {
+	static const struct msdos_sb_info sbi = {
 		.sec_per_clus = 4,
 		.data_start = 100,
 	};
@@ -34,7 +34,7 @@ static void fat_clus_to_blknr_test(struc
 
 static void fat_get_blknr_offset_test(struct kunit *test)
 {
-	struct msdos_sb_info sbi = {
+	static const struct msdos_sb_info sbi = {
 		.dir_per_block = 16,
 		.dir_per_block_bits = 4,
 	};
_

Patches currently in -mm which might be from arnd@arndb.de are

fat-avoid-stack-overflow-warning.patch
mm-damon-core-reduce-kernel-stack-usage.patch