On Thu, 2019-08-01 at 18:59 +0300, Leon Romanovsky wrote:
> > There's no need for a lockdep. The removal of the notifier callback
> > entry is re-entrant safe. The core removal routines have their own
> > spinlock they use to protect the actual notifier list. If you call
> > it
> > more than once, the second and subsequent calls merely scan the
> > list,
> > find no matching entry, and return ENOENT. The only reason this
> > might
> > need a lock and a lockdep entry is if you are protecting against a
> > race
> > with the *add* notifier code in the mlx5 driver specifically (the
> > core
> > add code won't have an issue, but since you only have a single place
> > to
> > store the notifier callback pointer, if it would be possible for you
> > to
> > add two callbacks and write over the first callback pointer with the
> > second without removing the first, then you would leak a callback
> > notifier in the core notifier list).
>
> atomic_notifier_chain_unregister() unconditionally calls to
> syncronize_rcu() and I'm not so sure that it is best thing to do
> for every port unbind.
>
> Actually, I'm completely lost here, we are all agree that the patch
> fixes issue correctly, and it returns the code to be exactly as
> it was before commit df097a278c75 ("IB/mlx5: Use the new mlx5 core
> notifier
> API"). Can we simply merge it and fix the kernel panic?
As long as you are OK with me adding a comment to the patch so people
coming back later won't scratch their head about how can it possible be
right to do that sequence without a lock held, I'm fine merging the fix.
Something like:
/*
* The check/unregister/set-NULL sequence below does not need to be
* locked for correctness as it's only an optimization, and can't
* be under a lock or will throw a scheduling while atomic error.
*/
--
Doug Ledford <dledford@xxxxxxxxxx>
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