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Date: Thu, 10 Nov 2022 19:00:52 +0100 From: Greg KH <gregkh@...uxfoundation.org> To: Chengming Zhou <zhouchengming@...edance.com> Cc: tj@...nel.org, linux-kernel@...r.kernel.org, syzbot+2fdf66e68f5f882c1074@...kaller.appspotmail.com Subject: Re: [PATCH] fs/kernfs: Fix lockdep warning in kernfs_active() On Wed, Nov 09, 2022 at 08:04:15PM +0800, Chengming Zhou wrote: > syzbot found a lockdep warning in kernfs_find_and_get_node_by_id(), > bisected to the commit c25491747b21 ("kernfs: Add KERNFS_REMOVING flags"), > which didn't hold kernfs_rwsem before call kernfs_active(kn). > > Since kernfs_find_and_get_node_by_id() doesn't have to get active count > of kn, only need to get a stable refcount of kn, so it should be enough > to just check kn has been KERNFS_ACTIVATED. > > Reported-by: syzbot+2fdf66e68f5f882c1074@...kaller.appspotmail.com > Fixes: c25491747b21 ("kernfs: Add KERNFS_REMOVING flags") > Signed-off-by: Chengming Zhou <zhouchengming@...edance.com> > --- > fs/kernfs/dir.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > index 6acd9c3d4cff..08f0f1570cd7 100644 > --- a/fs/kernfs/dir.c > +++ b/fs/kernfs/dir.c > @@ -705,7 +705,13 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root, > goto err_unlock; > } > > - if (unlikely(!kernfs_active(kn) || !atomic_inc_not_zero(&kn->count))) > + /* > + * ACTIVATED is protected with kernfs_mutex but it was clear when > + * @kn was added to idr and we just wanna see it set. No need to > + * grab kernfs_mutex. > + */ > + if (unlikely(!(kn->flags & KERNFS_ACTIVATED) || > + !atomic_inc_not_zero(&kn->count))) > goto err_unlock; > > spin_unlock(&kernfs_idr_lock); > -- > 2.37.2 > Shouldn't: https://lore.kernel.org/r/Y0SwqBsZ9BMmZv6x@slm.duckdns.org fix this instead?
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