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- Don't bother with s_stack_depth increasing to band-aid
    regressions in some composefs mount setups (EROFS + ovl^2)
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Merge tag 'erofs-for-6.19-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs fix from Gao Xiang:

 - Don't increase s_stack_depth which caused regressions in some
   composefs mount setups (EROFS + ovl^2)

   Instead just allow one extra unaccounted fs stacking level for
   straightforward cases.

* tag 'erofs-for-6.19-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: don't bother with s_stack_depth increasing for now
This commit is contained in:
Linus Torvalds 2026-01-09 19:34:50 -10:00
commit b6151c4e60
1 changed files with 12 additions and 6 deletions
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18
fs/erofs/super.c
View File

@ -644,14 +644,20 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
* fs contexts (including its own) due to self-controlled RO * fs contexts (including its own) due to self-controlled RO
* accesses/contexts and no side-effect changes that need to * accesses/contexts and no side-effect changes that need to
* context save & restore so it can reuse the current thread * context save & restore so it can reuse the current thread
* context. However, it still needs to bump `s_stack_depth` to * context.
* avoid kernel stack overflow from nested filesystems. * However, we still need to prevent kernel stack overflow due
* to filesystem nesting: just ensure that s_stack_depth is 0
* to disallow mounting EROFS on stacked filesystems.
* Note: s_stack_depth is not incremented here for now, since
* EROFS is the only fs supporting file-backed mounts for now.
* It MUST change if another fs plans to support them, which
* may also require adjusting FILESYSTEM_MAX_STACK_DEPTH.
*/ */
if (erofs_is_fileio_mode(sbi)) { if (erofs_is_fileio_mode(sbi)) {
sb->s_stack_depth = inode = file_inode(sbi->dif0.file);
file_inode(sbi->dif0.file)->i_sb->s_stack_depth + 1; if ((inode->i_sb->s_op == &erofs_sops && !sb->s_bdev) ||
if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) { inode->i_sb->s_stack_depth) {
erofs_err(sb, "maximum fs stacking depth exceeded"); erofs_err(sb, "file-backed mounts cannot be applied to stacked fses");
return -ENOTBLK; return -ENOTBLK;
} }
} }