Messages in this thread | | | Date | Tue, 3 Feb 2009 16:19:31 -0700 | From | Jonathan Corbet <> | Subject | Re: [PATCH 2/4] Convert epoll to a bitlock |
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On Tue, 3 Feb 2009 14:53:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> Well. We _could_ whack part of this nut with my usual hammer: protect > f_flags with file->f_dentry->d_inode->i_lock. IIRC there was some > objection to that - performance?
Andi has objected to the addition of locks, but i_lock is maybe sufficiently dispersed to pass muster there. I had an instinctive reaction to using a lock which is three pointers away, but I can get over that. I'll admit a bit of ignorance, though: if a given struct file exists, do we know for sure that file->f_dentry->d_inode exists?
> One problem here seems to be that we're trying to change multiple > things at the same time. We can blame the BKL for that. > > Can we break the problem into manageable chunks? Your patchset did > that, I guess. What were those chunks again? ;)
I'm not really sure how to break it down any further. If we take the i_lock approach, the chunks would be something like:
1) Use i_lock to protect accesses to f_flags. This would enable some BKL usage to be removed, but would not fix fasync.
2) Move responsibility for the FASYNC bit into ->fasync(), with fasync_helper() doing it in almost all situations. The remaining BKL usage would then go away.
3) The same optional fasync() return values cleanup.
Make sense?
jon
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