[PATCH RFC] udf: Mark LVID buffer as uptodate before marking it dirty in open/sync

When an I/O error occurs while writing the Logical Volume Integrity
Descriptor (LVID) buffer to the block device, the block layer's completion
handler (`end_buffer_write_sync()`) clears the `BH_Uptodate` flag on the
buffer. However, the buffer still contains valid LVID data in memory. If
the filesystem is subsequently remounted read-write or synced,
`udf_open_lvid()` or `udf_sync_fs()` will modify the LVID buffer and call
`mark_buffer_dirty()`. This triggers a spurious
`WARN_ON_ONCE(!buffer_uptodate(bh))` warning in `mark_buffer_dirty()`
because the buffer is not marked uptodate, even though its in-memory
contents are valid and are about to be overwritten.

To prevent this spurious warning, unconditionally set the `BH_Uptodate`
flag before calling `mark_buffer_dirty()` in `udf_open_lvid()` and
`udf_sync_fs()`. This acknowledges that the in-memory buffer is valid and
matches the workaround previously applied to `udf_close_lvid()` in commit
853a0c25baf9 ("udf: Mark LVID buffer as uptodate before marking it dirty").
Extending this workaround ensures consistent behavior across all LVID
updates.

Buffer I/O error on dev loop0, logical block 128, lost sync page write
------------[ cut here ]------------
!buffer_uptodate(bh)
WARNING: fs/buffer.c:1087 at mark_buffer_dirty+0x299/0x410 fs/buffer.c:1087
...
Call Trace:
 <TASK>
 udf_open_lvid+0x369/0x5b0 fs/udf/super.c:2078
 udf_reconfigure+0x336/0x540 fs/udf/super.c:679
 reconfigure_super+0x232/0x8f0 fs/super.c:1080
 vfs_cmd_reconfigure fs/fsopen.c:268 [inline]
 vfs_fsconfig_locked+0x171/0x320 fs/fsopen.c:297
 __do_sys_fsconfig fs/fsopen.c:463 [inline]
 __se_sys_fsconfig+0x6b9/0x810 fs/fsopen.c:350
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 </TASK>

Fixes: 853a0c25baf9 ("udf: Mark LVID buffer as uptodate before marking it dirty")
Assisted-by: Gemini:gemini-3.1-pro-preview Gemini:gemini-3-flash-preview syzbot
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=0306b38d9ed6ef71467d
Link: https://syzkaller.appspot.com/ai_job?id=83a8a238-e94a-44e6-8088-8640cf9cb7e0
To: "Jan Kara" <[email protected]>
To: <[email protected]>

---
diff --git a/fs/udf/super.c b/fs/udf/super.c
index cad2e15d6..7a5e9bd11 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -2075,6 +2075,12 @@ static void udf_open_lvid(struct super_block *sb)
 		UDF_SET_FLAG(sb, UDF_FLAG_INCONSISTENT);
 
 	udf_finalize_lvid(lvid);
+	/*
+	 * We set buffer uptodate unconditionally here to avoid spurious
+	 * warnings from mark_buffer_dirty() when previous EIO has marked
+	 * the buffer as !uptodate
+	 */
+	set_buffer_uptodate(bh);
 	mark_buffer_dirty(bh);
 	sbi->s_lvid_dirty = 0;
 	mutex_unlock(&sbi->s_alloc_mutex);
@@ -2397,6 +2403,12 @@ static int udf_sync_fs(struct super_block *sb, int wait)
 		 * Blockdevice will be synced later so we don't have to submit
 		 * the buffer for IO
 		 */
+		/*
+		 * We set buffer uptodate unconditionally here to avoid spurious
+		 * warnings from mark_buffer_dirty() when previous EIO has marked
+		 * the buffer as !uptodate
+		 */
+		set_buffer_uptodate(bh);
 		mark_buffer_dirty(bh);
 		sbi->s_lvid_dirty = 0;
 	}


base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
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