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Date: Fri, 26 Aug 2016 10:33:23 -0400 From: Waiman Long <waiman.long@....com> To: Peter Zijlstra <peterz@...radead.org> CC: Andreas Mohr <andi@...as.de>, Daniel Vetter <daniel.vetter@...el.com>, <linux-kernel@...r.kernel.org> Subject: Re: [RFC][PATCH -v2 1/4] locking/drm/i915: Kill mutex trickery On 08/26/2016 05:10 AM, Peter Zijlstra wrote: > On Fri, Aug 26, 2016 at 05:25:09AM +0200, Andreas Mohr wrote: >>> Another alternative is to provide a standard mutex API that returns the >>> owner of the lock if there is a real need for this capability. Peeking >>> into lock internal is not a good practice. > >> So, it seems the most we could provide which would offer a reliable, >> non-racy API protocol is something like: >> >> static bool mutex_is_locked_by_us(struct mutex *mutex) >> >> since during execution of this processing it would be guaranteed that: >> - either we do have the lock, thus *we* *RELIABLY* are and will be "the owner" >> - or we simply do not have it, thus *we* *RELIABLY* are and will be "not the owner" > Right, and that is exactly what they attempted and need. And the new > mutex implementation could actually do this much better than the old > one. > > But yes, such an interface should be part of the mutex implementation > proper, not something hacked on in random places. It is what exactly I have in mind. The actual API implemented is subject to negotiation. The important thing is that it has to be within the core mutex code. > Fwiw, the build bot seems to have found another instance of this thing > :/ drivers/gpu/drm/msm/msm_gem_shrinker.c includes an exact copy. This seems to be a new file that was introduced since 4.8. Cheers, Longman
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