+ fat-restore-original-value-when-fat_ent_write-failed.patch added to mm-nonmm-unstable branch

+ fat-restore-original-value-when-fat_ent_write-failed.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: fat: restore original value when fat_ent_write failed
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     fat-restore-original-value-when-fat_ent_write-failed.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fat-restore-original-value-when-fat_ent_write-failed.patch

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Yemu Lu <prcups@krgm.moe>
Subject: fat: restore original value when fat_ent_write failed
Date: Mon, 25 May 2026 16:56:49 +0800

fat_ent_write() may have committed the new link to the primary FAT but
then failed on the mirror copy, leaving the chain pointing to new_dclus
even though the caller will free it.  Restore the original value to keep
the chain consistent.

Link: https://lore.kernel.org/20260525085649.781643-1-n05ec@lzu.edu.cn
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Yemu Lu <prcups@krgm.moe>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Christian Brauner <brauner@kernel.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/fat/misc.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/fat/misc.c~fat-restore-original-value-when-fat_ent_write-failed
+++ a/fs/fat/misc.c
@@ -133,7 +133,11 @@ int fat_chain_add(struct inode *inode, i
 		ret = fat_ent_read(inode, &fatent, last);
 		if (ret >= 0) {
 			int wait = inode_needs_sync(inode);
+			int old = ret;
+
 			ret = fat_ent_write(inode, &fatent, new_dclus, wait);
+			if (ret < 0)
+				fat_ent_write(inode, &fatent, old, wait);
 			fatent_brelse(&fatent);
 		}
 		if (ret < 0)
_

Patches currently in -mm which might be from prcups@krgm.moe are

fat-restore-original-value-when-fat_ent_write-failed.patch