Greg KH wrote:
> 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 :)
But you're so much closer :) Did he push the mknod stuff too?
>>text from dmesg after BKL debugging patch:
>>release of recursive BKL hold, depth: 1
>>[ 0]main:492
>>[ 1]inode:149
>
> This means what?
BKL was acquired at main.c:492 and current->lock_depth was 0
then
BKL was acquired at inode.c:149 and current->lock_depth was 1
>>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?
Nope. I'm pretty sure that it isn't in a critical path anywhere, nor
are there any performance benefits. It is simply an annoying use that
is relatively easy to remove. It's kinda like using spaces instead of
tabs; most people won't notice, but some people really care :)
> I think that driverfs_mknod() needs some kind of protection now that you
> have removed it.
Do you just want to make sure it isn't called concurrently, or is
there some other BKL-protected area that you're concerned about.
driverfs_mknod() doesn't appear to be doing anything sneaky like
sleeping or calling itself, so I think a simple spinlock will work
just fine.
> Um, you used spaces, please use tabs like the rest of the file, and how
> Documentation/CodingStyle mandates.
Arg. I saw your talk twice so I really don't have an excuse. fix
attached.
-- 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 Thu Jul 4 00:22:54 2002 @@ -128,6 +128,7 @@ return inode; } +static spinlock_t driverfs_mknod_lock = SPIN_LOCK_UNLOCKED; static int driverfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev) { struct inode *inode = driverfs_get_inode(dir->i_sb, mode, dev); @@ -146,20 +147,20 @@ static int driverfs_mkdir(struct inode *dir, struct dentry *dentry, int mode) { int res; - lock_kernel(); dentry->d_op = &driverfs_dentry_dir_ops; + spin_lock(&driverfs_mknod_lock); res = driverfs_mknod(dir, dentry, mode | S_IFDIR, 0); - unlock_kernel(); + spin_unlock(&driverfs_mknod_lock); 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; + spin_lock(&driverfs_mknod_lock); res = driverfs_mknod(dir, dentry, mode | S_IFREG, 0); - unlock_kernel(); + spin_unlock(&driverfs_mknod_lock); return res; } @@ -211,9 +212,9 @@ 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 +354,9 @@ 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 +373,7 @@ default: break; } - unlock_kernel(); + up(&inode->i_sem); return retval; }
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This archive was generated by hypermail 2b29 : Sun Jul 07 2002 - 22:00:12 EST