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SubjectRe: Remaining BKL users, what to do
On Thursday 16 September 2010 21:00:25 Jan Harkes wrote:
> > Just removing the BKL without the Coda community seems like a heap
> > of pointless work.
> It depends, it might get rid of that mount lockup. There shouldn't be
> too much shared state because the kernel module mostly just forwards
> requests to userspace and the BKL right now seems to be mostly used to
> protects access to the upcall lists and could probably without too much
> trouble be replaced with a single 'global' (but Coda-only) or
> mount-point specific mutex.

Ok, that would be nice.

There are two strategies forward then based on the current code:

1. introduce a global or per-superblock mutex and convert all
instances of lock-kernel to that, then see what breaks (lockdep
helps here) and fix up all places where you get potential
deadlocks. The easiest replacement would be the existing superblock
mutex, doing s/lock_kernel()/lock_super(sb)/.

2. understand what data structures are actually being protected
by the BKL right now, then add proper locking around all accesses
to them and finally remove all uses of the BKL.


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