Re: [PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[Baokun Li]

On 2024/3/7 22:18, Gao Xiang wrote:
> On 2024/3/7 18:10, Baokun Li wrote:
> > Lockdep reported the following issue when mounting erofs with a 
> > domain_id:
> >
> > ============================================
> > WARNING: possible recursive locking detected
> > 6.8.0-rc7-xfstests #521 Not tainted
> > --------------------------------------------
> > mount/396 is trying to acquire lock:
> > ffff907a8aaaa0e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
> >                         at: alloc_super+0xe3/0x3d0
> >
> > but task is already holding lock:
> > ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
> >                         at: alloc_super+0xe3/0x3d0
> >
> > other info that might help us debug this:
> >   Possible unsafe locking scenario:
> >
> >         CPU0
> >         ----
> >    lock(&type->s_umount_key#50/1);
> >    lock(&type->s_umount_key#50/1);
> >
> >   *** DEADLOCK ***
> >
> >   May be due to missing lock nesting notation
> >
> > 2 locks held by mount/396:
> >   #0: ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
> >             at: alloc_super+0xe3/0x3d0
> >   #1: ffffffffc00e6f28 (erofs_domain_list_lock){+.+.}-{3:3},
> >             at: erofs_fscache_register_fs+0x3d/0x270 [erofs]
> >
> > stack backtrace:
> > CPU: 1 PID: 396 Comm: mount Not tainted 6.8.0-rc7-xfstests #521
> > Call Trace:
> >   <TASK>
> >   dump_stack_lvl+0x64/0xb0
> >   validate_chain+0x5c4/0xa00
> >   __lock_acquire+0x6a9/0xd50
> >   lock_acquire+0xcd/0x2b0
> >   down_write_nested+0x45/0xd0
> >   alloc_super+0xe3/0x3d0
> >   sget_fc+0x62/0x2f0
> >   vfs_get_super+0x21/0x90
> >   vfs_get_tree+0x2c/0xf0
> >   fc_mount+0x12/0x40
> >   vfs_kern_mount.part.0+0x75/0x90
> >   kern_mount+0x24/0x40
> >   erofs_fscache_register_fs+0x1ef/0x270 [erofs]
> >   erofs_fc_fill_super+0x213/0x380 [erofs]
> >
> > This is because the file_system_type of both erofs and the pseudo-mount
> > point of domain_id is erofs_fs_type, so two successive calls to
> > alloc_super() are considered to be using the same lock and trigger the
> > warning above.
> >
> > Therefore add a nodev file_system_type called erofs_anon_fs_type in
> > fscache.c to silence this complaint. Because kern_mount() takes a
> > pointer to struct file_system_type, not its (string) name. So we don't
> > need to call register_filesystem(). In addition, call init_pseudo() in
> > erofs_anon_init_fs_context() as suggested by Al Viro, so that we can
> > remove erofs_fc_fill_pseudo_super(), erofs_fc_anon_get_tree(), and
> > erofs_anon_context_ops.
> >
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
>
> I will add
>
> Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>
> when applying..
Okay, thanks for adding it.
> Also since it's a false positive and too close to the
> final so let's keep this patch in -next for a while and
> then aim for v6.9-rc1 instead.
>
> Thanks,
> Gao Xiang
Fine! Thanks!
--
With Best Regards,
Baokun Li
.