On Sat, Sep 18, 2010 at 03:09:31PM +0200, Arnd Bergmann wrote:
> This prepares the removal of the big kernel lock from the
> file locking code. We still use the BKL as long as fs/lockd
> uses it and ceph might sleep, but we can flip the definition
> to a private spinlock as soon as that's done.
> All users outside of fs/lockd get converted to use
> lock_flocks() instead of lock_kernel() where appropriate.
>
> Based on an earlier patch to use a spinlock from Matthew
> Wilcox, who has attempted this a few times before. An even
> earlier attempt to use a semaphore instead of the BKL
> apparently was made by Andrew Morton about ten years ago,
> but reverted for performance reasons.
>
> Someone should do some serious performance testing when
> this becomes a spinlock, since this has caused problems
> before. Using a spinlock should be at least as good
> as the BKL in theory, but who knows...
>
> If nobody has any objections to this preparation patch,
> I'd like to add it to my bkl/vfs tree and into -next.
Looks good to me.
> EXPORT_SYMBOL(posix_test_lock);
> @@ -730,18 +746,16 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
> int error = 0;
> int found = 0;
>
> - lock_kernel();
> - if (request->fl_flags & FL_ACCESS)
> - goto find_conflict;
> -
> - if (request->fl_type != F_UNLCK) {
> - error = -ENOMEM;
> + if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {
> new_fl = locks_alloc_lock();
> - if (new_fl == NULL)
> - goto out;
> - error = 0;
> + if (!new_fl)
> + return -ENOMEM;
> }
>
> + lock_flocks();
> + if (request->fl_flags & FL_ACCESS)
> + goto find_conflict;
> +
I might have left this to a separate patch, but OK.
--b.
> for_each_lock(inode, before) {
> struct file_lock *fl = *before;
> if (IS_POSIX(fl))
> @@ -767,8 +781,11 @@ static int flock_lock_file(struct file *filp, struct file_lock *request)
> * If a higher-priority process was blocked on the old file lock,
> * give it the opportunity to lock the file.
> */
> - if (found)
> + if (found) {
> + unlock_flocks();
> cond_resched();
> + lock_flocks();
> + }
>
> find_conflict:
> for_each_lock(inode, before) {
--
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