6a79d84840
As we need to take a walk back along the signaler timeline to find the fence before upon which we want to wait, we need to lock that timeline to prevent it being modified as we walk. Similarly, we also need to acquire a reference to the earlier fence while it still exists! Though we lack the correct locking today, we are saved by the overarching struct_mutex -- but that protection is being removed. v2: Tvrtko made me realise I was being lax and using annotations to ignore the AB-BA deadlock from the timeline overlap. As it would be possible to construct a second request that was using a semaphore from the same timeline as ourselves, we could quite easily end up in a situation where we deadlocked in our mutex waits. Avoid that by using a trylock and falling back to a normal dma-fence await if contended. v3: Eek, the signal->timeline is volatile and must be carefully dereferenced to ensure it is valid. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190919111912.21631-2-chris@chris-wilson.co.uk
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.