Re: 6.7.0-rc1 + hacks deadlock bug, wifi netdev delete + cat of debugfs file.

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2023-11-08 at 12:04 -0800, Ben Greear wrote:
> On 11/8/23 10:43, Johannes Berg wrote:
> > On Wed, 2023-11-08 at 09:44 -0800, Ben Greear wrote:
> > > 
> > > This method appears to actually set a S_DEAD flag in the dentry,
> > > 
> > 
> > A *dir* entry.
> > 
> > >   so maybe
> > > we just check that flag in the mutex_trylock failed to acquire path
> > > in the debugfs read?
> > > 
> > > void simple_recursive_removal(struct dentry *dentry,
> > >                                 void (*callback)(struct dentry *))
> > > {
> > > 	struct dentry *this = dget(dentry);
> > > 	while (true) {
> > > 		struct dentry *victim = NULL, *child;
> > > 		struct inode *inode = this->d_inode;
> > > 
> > > 		inode_lock(inode);
> > > 		if (d_is_dir(this))
> > > 			inode->i_flags |= S_DEAD;
> > > 
> > 
> > But even if you did that, I'm not sure what you'd do? trylock and sleep,
> > and abort if you find it's being removed? That all sounds super awkward.
> 
> Here is my compile-only tested approach.  It only tries to fix one particular
> locking case in debugfs, so I'm sure it is not yet complete.  I believe I
> need to add that new flag in the fs.h, as S_DEAD is only for directories,
> if I understand the code properly.

[snip code]

Sure, it's just software. You can do whatever you want with it. But ...
there's no way anything even similar to this will ever go upstream.

johannes