Re: [PATCH 2/2] lockdep: Up MAX_LOCKDEP_CHAINS

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Daniel Vetter (2017-11-29 09:46:36)
> cross-release ftl
> 
> From Chris:
> 
> "Fwiw, this isn't cross-release but us reloading the module many times,
> creating a whole host of new lockclasses. Even more fun is when the
> module gets a slightly different address and the new lock address hashes
> into an old lock...
> 
> "I did think about a module-hook to revoke the stale lockclasses, but
> that still leaves all the hashed chains.
> 
> "This particular nuisance was temporarily pushed back by teaching igt not
> to reload i915.ko on a whim."
> 
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Marta Lofstedt <marta.lofstedt@intel.com>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=103707
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Yes, I think we need to carry this for CI. cross-release will add many
more chains, and since we already exhausted the previous array we will
need more (and just reducing the number of module reloads only gives a
temporary respite). Doubling the array doesn't seem like it'll buy us
much time though? Could we afford 20 bits? Might we not also need to
expand the lockclasses array? That we could just double?

In principle acked-by for core-for-CI, I think we need a bit surer
ground before saying that in general lockdep needs a larger array.
-Chris
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