Re: [PATCH] remove BKL from driverfs

[Patrick Mochel]

> > I see no reason to hold the BKL in your situation.  I replaced it with 
> > i_sem in some places and just plain removed it in others.  I believe 
> > that you get all of the protection that you need from dcache_lock in 
> > the dentry insert and activate.  Can you prove me wrong?
> 
> No, and I'm not about to try very hard. It appears that the place you 
> removed it should be fine. In driverfs_unlink, you replace it with i_sem. 
> ramfs, which driverfs mimmicks, doesn't hold any lock during unlink. It 
> seems it could be removed altogether. 

Actually, taking i_sem is completely wrong. Look at vfs_unlink() in 
fs/namei.c:

        down(&dentry->d_inode->i_sem);
        if (d_mountpoint(dentry))
                error = -EBUSY;
        else {
                error = dir->i_op->unlink(dir, dentry);
                if (!error)
                        d_delete(dentry);
        }
        up(&dentry->d_inode->i_sem);

Then, in driverfs_unlink:

	struct inode *inode = dentry->d_inode;

	down(&inode->i_sem);    

You didn't test this on file removal did you? A good way to verify that 
you have most of your bases covered is to plug/unplug a USB device a few 
times. I learned that one from Greg, and it's caught several bugs.

Anyway, I say that the lock can be removed altogether. Ditto for mknod as 
well.

	-pat