[Bug 111882] [CI][SHARDS] GLK: igt at gem_eio@kms - dmesg-warn - WARNING: possible circular locking dependency detected

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111882

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
commit b1e3177bd1d8f41e2a9cc847e56a96cdc0eefe62
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Oct 4 14:40:00 2019 +0100

    drm/i915: Coordinate i915_active with its own mutex

    Forgo the struct_mutex serialisation for i915_active, and interpose its
    own mutex handling for active/retire.

    This is a multi-layered sleight-of-hand. First, we had to ensure that no
    active/retire callbacks accidentally inverted the mutex ordering rules,
    nor assumed that they were themselves serialised by struct_mutex. More
    challenging though, is the rule over updating elements of the active
    rbtree. Instead of the whole i915_active now being serialised by
    struct_mutex, allocations/rotations of the tree are serialised by the
    i915_active.mutex and individual nodes are serialised by the caller
    using the i915_timeline.mutex (we need to use nested spinlocks to
    interact with the dma_fence callback lists).

    The pain point here is that instead of a single mutex around execbuf, we
    now have to take a mutex for active tracker (one for each vma, context,
    etc) and a couple of spinlocks for each fence update. The improvement in
    fine grained locking allowing for multiple concurrent clients
    (eventually!) should be worth it in typical loads.

    v2: Add some comments that barely elucidate anything :(

    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-6-chris@chris-wilson.co.uk

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