Re: [External] Re: [PATCH V2 4/5] erofs: remove duplicated unregister_cookie

[Jia Zhu]

在 2022/9/9 18:28, JeffleXu 写道:
> On 9/9/22 5:55 PM, JeffleXu wrote:
> > On 9/2/22 6:53 PM, Jia Zhu wrote:
> > > In erofs umount scenario, erofs_fscache_unregister_cookie() is called
> > > twice in kill_sb() and put_super().
> > >
> > > It works for original semantics, cause 'ctx' will be set to NULL in
> > > put_super() and will not be unregister again in kill_sb().
> > > However, in shared domain scenario, we use refcount to maintain the
> > > lifecycle of cookie. Unregister the cookie twice will cause it to be
> > > released early.
>
> Sorry, why can't we also set sbi->s_fscache to NULL after decrementing
> the refcount in shared domain mode, to avoid the refcount being
> decremented twice?
In below case:
1. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o 
domain_id=1 mnt
2. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o 
domain_id=1 mnt2
3. Procedure 2 will fail since we can't mount erofs with the same sysfs
entry.
4. Mount()'s error handling path will step into put_super().
5. Domain's refcnt will be decremented even if it has not yet
been incremented.
> > > For the above reasons, this patch removes duplicate unregister_cookie
> > > and move fscache_unregister_* before shotdown_super() to prevent busy
> > > inode(ctx->inode) when umount.
> > >
> > > Signed-off-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
> > > ---
> > >   fs/erofs/super.c | 16 ++++++++--------
> > >   1 file changed, 8 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> > > index 69de1731f454..667a78f0ee70 100644
> > > --- a/fs/erofs/super.c
> > > +++ b/fs/erofs/super.c
> > > @@ -919,19 +919,20 @@ static void erofs_kill_sb(struct super_block *sb)
> > >   		kill_litter_super(sb);
> > >   		return;
> > >   	}
> > > -	if (erofs_is_fscache_mode(sb))
> > > -		generic_shutdown_super(sb);
> > > -	else
> > > -		kill_block_super(sb);
> > > -
> > >   	sbi = EROFS_SB(sb);
> > >   	if (!sbi)
> > >   		return;
> > >   
> > > +	if (erofs_is_fscache_mode(sb)) {
> > > +		erofs_fscache_unregister_cookie(&sbi->s_fscache);
> > > +		erofs_fscache_unregister_fs(sb);
> > > +		generic_shutdown_super(sb);
> >
> > Generally we can't do clean ups before generic_shutdown_super(), since
> > generic_shutdown_super() may trigger IO, e.g. in sync_filesystem(),
> > though it's not the case for erofs (read-only).
> >
> > How about embedding erofs_fscache_unregister_cookie() into
> > erofs_fscache_unregister_fs(), and thus we can check domain_id in
> > erofs_fscache_unregister_fs()?
> >
> > > +	} else {
> > > +		kill_block_super(sb);
> > > +	}
> > > +
> > >   	erofs_free_dev_context(sbi->devs);
> > >   	fs_put_dax(sbi->dax_dev, NULL);
> > > -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
> > > -	erofs_fscache_unregister_fs(sb);
> > >   	kfree(sbi->opt.fsid);
> > >   	kfree(sbi->opt.domain_id);
> > >   	kfree(sbi);
> > > @@ -951,7 +952,6 @@ static void erofs_put_super(struct super_block *sb)
> > >   	iput(sbi->managed_cache);
> > >   	sbi->managed_cache = NULL;
> > >   #endif
> > > -	erofs_fscache_unregister_cookie(&sbi->s_fscache);
> > >   }
> > >   
> > >   struct file_system_type erofs_fs_type = {