Re: [PATCH] remove BKL from driverfs

Greg KH
2002-07-04T07:09:07Z

On Wed, Jul 03, 2002 at 11:26:27PM -0700, Dave Hansen wrote:
> I saw your talk about driverfs at OLS and it got my attention. When
> my BKL debugging patch showed some use of the BKL in driverfs, I was
> very dissapointed (you can blame Greg if you want).

Blame me? Al Viro pushed that BKL into the file, not I :)

> text from dmesg after BKL debugging patch:
> release of recursive BKL hold, depth: 1
> [ 0]main:492
> [ 1]inode:149

This means what?

> 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?

I see no reason to really care :)
Can you prove that driverfs (or pcihpfs or usbfs) accesses are on a
critical path that removing the BKL usage here actually helps?

> --- linux-2.5.24-clean/fs/driverfs/inode.c Thu Jun 20 15:53:45 2002
> +++ linux/fs/driverfs/inode.c Wed Jul 3 23:18:23 2002
> @@ -146,20 +146,16 @@
> static int driverfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
> {
> int res;
> - lock_kernel();
> dentry->d_op = &driverfs_dentry_dir_ops;
> res = driverfs_mknod(dir, dentry, mode | S_IFDIR, 0);
> - unlock_kernel();
> return res;
> }

I think that driverfs_mknod() needs some kind of protection now that you
have removed it.

>
> static int driverfs_create(struct inode *dir, struct dentry *dentry, int mode)
> {
> int res;
> - lock_kernel();
> dentry->d_op = &driverfs_dentry_file_ops;
> res = driverfs_mknod(dir, dentry, mode | S_IFREG, 0);
> - unlock_kernel();
> return res;
> }
>
> @@ -211,9 +207,9 @@
> if (driverfs_empty(dentry)) {
> struct inode *inode = dentry->d_inode;
>
> - lock_kernel();
> + down(&inode->i_sem);
> inode->i_nlink--;
> - unlock_kernel();
> + up(&inode->i_sem);
> dput(dentry);
> error = 0;
> }
> @@ -353,8 +349,9 @@
> driverfs_file_lseek(struct file *file, loff_t offset, int orig)
> {
> loff_t retval = -EINVAL;
> + struct inode *inode = file->f_dentry->d_inode->i_mapping->host;

Um, you used spaces, please use tabs like the rest of the file, and how
Documentation/CodingStyle mandates.

thanks,

greg k-h