Re: [PATCH] debugfs: fix potential infinite loop in debugfs_remove_recursive

[yukuai (C)]

å 2019/11/15 9:47, yukuai (C) åé:
> On 2019/11/14 22:34, Steven Rostedt wrote:
> > On Thu, 14 Nov 2019 14:59:04 +0800
> > "yukuai (C)" <yukuai3@xxxxxxxxxx> wrote:
> >
> > > > Have you tried this patch with lockdep enabled and tried to hit this
> > > > code path?
> >
> > > You are right, I get the results with lockdep enabled:
> >
> > That was what I was afraid of :-(
> >
> > > [ÂÂ 64.314748] ============================================
> > > [ÂÂ 64.315568] WARNING: possible recursive locking detected
> > > [ÂÂ 64.316549] 5.4.0-rc7-dirty #5 Tainted: GÂÂÂÂÂÂÂÂÂÂ O
> > > [ÂÂ 64.317398] --------------------------------------------
> > > [ÂÂ 64.318230] rmmod/2607 is trying to acquire lock:
> >
> > > The warning will disappeare by adding
> > > lockdep_set_novalidate_class(&child->d_lock) before calling
> > > simple_empty(child). But I'm not sure It's the right modfication.
> >
> > I'm wondering if we should add a simple_empty_unlocked() that does
> > simple_empty() without taking the lock, to allow us to call
> > spin_lock_nested() on the child. Of course, I don't know how much
> > nesting we allow as it calls the nesting too.
> Do you think we can do this:
> 1. add a new enum type for dentry_d_lock_class:
> enum dentry_d_lock_class
> {
>  ÂÂÂÂDENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */
>  ÂÂÂÂDENTRY_D_LOCK_NESTED
missing a ','
>  ÂÂÂÂDENTRY_D_LOCK_NESTED_1 /* maybe another name */
> };
> 2. use the new enum type in simple_empty
> int simple_empty(struct dentry *dentry)
> {
>  ÂÂÂÂspin_lock(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
should be 'spin_lock_nested'
>  ÂÂÂÂlist_for_each_entry(child, &dentry->d_subdirs, d_child) {
>  ÂÂÂÂÂÂÂ spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED_1);
> }
>
> If you agree, I'll try to send a patch or patchset(with modification in 
> debugfs_remove_recursive).
sorry about the stupid mistake..

Thanks!
Yu Kuai