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Previously, we were able to rely on the recursive properties of struct_mutex to allow us to serialise revoking mmaps and reacquiring the FENCE registers with them being clobbered over a global device reset. I then proceeded to throw out the baby with the bath water in order to pursue a struct_mutex-less reset. Perusing LWN for alternative strategies, the dilemma on how to serialise access to a global resource on one side was answered by https://lwn.net/Articles/202847/ -- Sleepable RCU: 1 int readside(void) { 2 int idx; 3 rcu_read_lock(); 4 if (nomoresrcu) { 5 rcu_read_unlock(); 6 return -EINVAL; 7 } 8 idx = srcu_read_lock(&ss); 9 rcu_read_unlock(); 10 /* SRCU read-side critical section. */ 11 srcu_read_unlock(&ss, idx); 12 return 0; 13 } 14 15 void cleanup(void) 16 { 17 nomoresrcu = 1; 18 synchronize_rcu(); 19 synchronize_srcu(&ss); 20 cleanup_srcu_struct(&ss); 21 } No more worrying about stop_machine, just an uber-complex mutex, optimised for reads, with the overhead pushed to the rare reset path. However, we do run the risk of a deadlock as we allocate underneath the SRCU read lock, and the allocation may require a GPU reset, causing a dependency cycle via the in-flight requests. We resolve that by declaring the driver wedged and cancelling all in-flight rendering. v2: Use expedited rcu barriers to match our earlier timing characteristics. v3: Try to annotate locking contexts for sparse v4: Reduce selftest lock duration to avoid a reset deadlock with fences v5: s/srcu/reset_backoff_srcu/ v6: Remove more stale comments Testcase: igt/gem_mmap_gtt/hang Fixes: eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex") Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190208153708.20023-2-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.