Commit 7893cc12251f for kernel

commit 7893cc12251f6f19e7689a4cf3ba803bddbd8437
Author: Gao Xiang <xiang@kernel.org>
Date:   Sat Jan 10 19:47:03 2026 +0800

    erofs: fix file-backed mounts no longer working on EROFS partitions

    Sheng Yong reported [1] that Android APEX images didn't work with commit
    072a7c7cdbea ("erofs: don't bother with s_stack_depth increasing for
    now") because "EROFS-formatted APEX file images can be stored within an
    EROFS-formatted Android system partition."

    In response, I sent a quick fat-fingered [PATCH v3] to address the
    report.  Unfortunately, the updated condition was incorrect:

             if (erofs_is_fileio_mode(sbi)) {
    -            sb->s_stack_depth =
    -                file_inode(sbi->dif0.file)->i_sb->s_stack_depth + 1;
    -            if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
    -                erofs_err(sb, "maximum fs stacking depth exceeded");
    +            inode = file_inode(sbi->dif0.file);
    +            if ((inode->i_sb->s_op == &erofs_sops && !sb->s_bdev) ||
    +                inode->i_sb->s_stack_depth) {

    The condition `!sb->s_bdev` is always true for all file-backed EROFS
    mounts, making the check effectively a no-op.

    The real fix tested and confirmed by Sheng Yong [2] at that time was
    [PATCH v3 RESEND], which correctly ensures the following EROFS^2 setup
    works:
        EROFS (on a block device) + EROFS (file-backed mount)

    But sadly I screwed it up again by upstreaming the outdated [PATCH v3].

    This patch applies the same logic as the delta between the upstream
    [PATCH v3] and the real fix [PATCH v3 RESEND].

    Reported-by: Sheng Yong <shengyong1@xiaomi.com>
    Closes: https://lore.kernel.org/r/3acec686-4020-4609-aee4-5dae7b9b0093@gmail.com [1]
    Fixes: 072a7c7cdbea ("erofs: don't bother with s_stack_depth increasing for now")
    Link: https://lore.kernel.org/r/243f57b8-246f-47e7-9fb1-27a771e8e9e8@gmail.com [2]
    Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index e93264034b5d..5136cda5972a 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -655,7 +655,8 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 		 */
 		if (erofs_is_fileio_mode(sbi)) {
 			inode = file_inode(sbi->dif0.file);
-			if ((inode->i_sb->s_op == &erofs_sops && !sb->s_bdev) ||
+			if ((inode->i_sb->s_op == &erofs_sops &&
+			     !inode->i_sb->s_bdev) ||
 			    inode->i_sb->s_stack_depth) {
 				erofs_err(sb, "file-backed mounts cannot be applied to stacked fses");
 				return -ENOTBLK;