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Subject[PATCH] remove BKL from driverfs
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).

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

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?

--
Dave Hansen
haveblue@us.ibm.com
--- 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;
}

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;

- lock_kernel();
+ down(&inode->i_sem);
switch(orig) {
case 0:
if (offset > 0) {
@@ -371,7 +368,7 @@
default:
break;
}
- unlock_kernel();
+ up(&inode->i_sem);
return retval;
}
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