On 2023/7/31 20:43, Christian Brauner wrote:
On Mon, Jul 31, 2023 at 01:16:22PM +0200, Christoph Hellwig wrote:
On Mon, Jul 31, 2023 at 06:58:14PM +0800, Gao Xiang wrote:
Previously, deactivate_locked_super() or .kill_sb() will only be
called after fill_super is called, and .s_magic will be set at
the very beginning of erofs_fc_fill_super().
After ("fs: open block device after superblock creation"), such
convension is changed now. Yet at a quick glance,
WARN_ON(sb->s_magic != EROFS_SUPER_MAGIC);
in erofs_kill_sb() can be removed since deactivate_locked_super()
will also be called if setup_bdev_super() is falled. I'd suggest
that removing this WARN_ON() in the related commit, or as
a following commit of the related branch of the pull request if
possible.
Agreed. I wonder if we should really call into ->kill_sb before
calling into fill_super, but I need to carefull look into the
details.
I think checking for s_magic in erofs kill sb is wrong as it introduces
a dependency on both fill_super() having been called and that s_magic is
initialized first. If someone reorders erofs_kill_sb() such that s_magic
is only filled in once everything else succeeded it would cause the same
bug. That doesn't sound nice to me.
Many many years ago, strange .kill_sb called on our smartphone products
without proper call chain. That was why it was added and s_magic was
initialized first and at least it reminds a slight behavior change for
us (this time).
Anyway, I also think it's almost useless upstream so I'm fine to drop
this WARN_ON().
Thanks,
Gao Xiang
I think ->fill_super() should only be called after successfull
superblock allocation and after the device has been successfully opened.
Just as this code does now. So ->kill_sb() should only be called after
we're guaranteed that ->fill_super() has been called.
We already mostly express that logic through the fs_context object.
Anything that's allocated in fs_context->init_fs_context() is freed in
fs_context->free() before fill_super() is called. After ->fill_super()
is called fs_context->s_fs_info will have been transferred to
sb->s_fs_info and will have to be killed via ->kill_sb().
Does that make sense?
