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Chris Wilson df9f85d858 drm/i915: Serialise i915_active_fence_set() with itself The expected downside to commit `58b4c1a07a` ("drm/i915: Reduce nested prepare_remote_context() to a trylock") was that it would need to return -EAGAIN to userspace in order to resolve potential mutex inversion. Such an unsightly round trip is unnecessary if we could atomically insert a barrier into the i915_active_fence, so make it happen. Currently, we use the timeline->mutex (or some other named outer lock) to order insertion into the i915_active_fence (and so individual nodes of i915_active). Inside __i915_active_fence_set, we only need then serialise with the interrupt handler in order to claim the timeline for ourselves. However, if we remove the outer lock, we need to ensure the order is intact between not only multiple threads trying to insert themselves into the timeline, but also with the interrupt handler completing the previous occupant. We use xchg() on insert so that we have an ordered sequence of insertions (and each caller knows the previous fence on which to wait, preserving the chain of all fences in the timeline), but we then have to cmpxchg() in the interrupt handler to avoid overwriting the new occupant. The only nasty side-effect is having to temporarily strip off the RCU-annotations to apply the atomic operations, otherwise the rules are much more conventional! Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112402 Fixes: `58b4c1a07a` ("drm/i915: Reduce nested prepare_remote_context() to a trylock") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191127134527.3438410-1-chris@chris-wilson.co.uk		2019-11-27 17:02:14 +00:00
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README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.