+ nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse.patch added to mm-hotfixes-unstable branch

+ nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: nilfs2: fix WARNING in mark_buffer_dirty due to discarded buffer reuse
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse.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: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Subject: nilfs2: fix WARNING in mark_buffer_dirty due to discarded buffer reuse
Date: Fri, 18 Aug 2023 22:18:04 +0900

A syzbot stress test using a corrupted disk image reported that
mark_buffer_dirty() called from __nilfs_mark_inode_dirty() or
nilfs_palloc_commit_alloc_entry() may output a kernel warning, and can
panic if the kernel is booted with panic_on_warn.

This is because nilfs2 keeps buffer pointers in local structures for some
metadata and reuses them, but such buffers may be forcibly discarded by
nilfs_clear_dirty_page() in some critical situations.

This issue is reported to appear after commit 28a65b49eb53 ("nilfs2: do
not write dirty data after degenerating to read-only"), but the issue has
potentially existed before.

Fix this issue by checking the uptodate flag when attempting to reuse an
internally held buffer, and reloading the metadata instead of reusing the
buffer if the flag was lost.

Link: https://lkml.kernel.org/r/20230818131804.7758-1-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+cdfcae656bac88ba0e2d@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/0000000000003da75f05fdeffd12@google.com
Fixes: 8c26c4e2694a ("nilfs2: fix issue with flush kernel thread after remount in RO mode because of driver's internal error or metadata corruption")
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/nilfs2/alloc.c |    3 ++-
 fs/nilfs2/inode.c |    7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

--- a/fs/nilfs2/alloc.c~nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse
+++ a/fs/nilfs2/alloc.c
@@ -205,7 +205,8 @@ static int nilfs_palloc_get_block(struct
 	int ret;
 
 	spin_lock(lock);
-	if (prev->bh && blkoff == prev->blkoff) {
+	if (prev->bh && blkoff == prev->blkoff &&
+	    likely(buffer_uptodate(prev->bh))) {
 		get_bh(prev->bh);
 		*bhp = prev->bh;
 		spin_unlock(lock);
--- a/fs/nilfs2/inode.c~nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse
+++ a/fs/nilfs2/inode.c
@@ -1025,7 +1025,7 @@ int nilfs_load_inode_block(struct inode
 	int err;
 
 	spin_lock(&nilfs->ns_inode_lock);
-	if (ii->i_bh == NULL) {
+	if (ii->i_bh == NULL || unlikely(!buffer_uptodate(ii->i_bh))) {
 		spin_unlock(&nilfs->ns_inode_lock);
 		err = nilfs_ifile_get_inode_block(ii->i_root->ifile,
 						  inode->i_ino, pbh);
@@ -1034,7 +1034,10 @@ int nilfs_load_inode_block(struct inode
 		spin_lock(&nilfs->ns_inode_lock);
 		if (ii->i_bh == NULL)
 			ii->i_bh = *pbh;
-		else {
+		else if (unlikely(!buffer_uptodate(ii->i_bh))) {
+			__brelse(ii->i_bh);
+			ii->i_bh = *pbh;
+		} else {
 			brelse(*pbh);
 			*pbh = ii->i_bh;
 		}
_

Patches currently in -mm which might be from konishi.ryusuke@gmail.com are

nilfs2-fix-general-protection-fault-in-nilfs_lookup_dirty_data_buffers.patch
nilfs2-fix-warning-in-mark_buffer_dirty-due-to-discarded-buffer-reuse.patch