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In order to ensure that all invalidations are completed before the operation returns to userspace (i.e. before the munmap() syscall returns) we need to wait upon the outstanding operations. We are allowed to block inside the invalidate_range_start callback, and as struct_mutex is the inner lock with mmap_sem we can wait upon the struct_mutex without provoking lockdep into warning about a deadlock. However, we don't actually want to wait upon outstanding rendering whilst holding the struct_mutex if we can help it otherwise we also block other processes from submitting work to the GPU. So first we do a wait without the lock and then when we reacquire the lock, we double check that everything is ready for removing the invalidated pages. Finally to wait upon the outstanding unpinning tasks, we create a private workqueue as a means to conveniently wait upon all at once. The drawback is that this workqueue is per-mm, so any threads concurrently invalidating objects will wait upon each other. The advantage of using the workqueue is that we can wait in parallel for completion of rendering and unpinning of several objects (of particular importance if the process terminates with a whole mm full of objects). v2: Apply a cup of tea to the changelog. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94699 Testcase: igt/gem_userptr_blits/sync-unmap-cycles Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Michał Winiarski <michal.winiarski@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/1459864801-28606-1-git-send-email-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> |
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