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Filename Latest commit message Latest commit date
Chris Wilson 18afa28892 Revert "drm/i915: Skip execlists_dequeue() early if the list is empty"
This reverts commit 6c943de668 ("drm/i915: Skip execlists_dequeue()
early if the list is empty").

The validity of using READ_ONCE there depends upon having a mb to
coordinate the assignment of engine->execlist_first inside
submit_request() and checking prior to taking the spinlock in
execlists_dequeue(). We wrote "the update to TASKLET_SCHED incurs a
memory barrier making this cross-cpu checking safe", but failed to
notice that this mb was *conditional* on the execlists being ready, i.e.
there wasn't the required mb when it was most necessary!

We could install an unconditional memory barrier to fixup the
READ_ONCE():

diff --git a/drivers/gpu/drm/i915/intel_lrc.c
b/drivers/gpu/drm/i915/intel_lrc.c
index 7dd732cb9f57..1ed164b16d44 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -616,6 +616,7 @@ static void execlists_submit_request(struct
drm_i915_gem_request *request)

        if (insert_request(&request->priotree, &engine->execlist_queue))
{
                engine->execlist_first = &request->priotree.node;
+               smp_wmb();
                if (execlists_elsp_ready(engine))

But we have opted to remove the race as it should be rarely effective,
and saves us having to explain the necessary memory barriers which we
quite clearly failed at.

Reported-and-tested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Fixes: 6c943de668 ("drm/i915: Skip execlists_dequeue() early if the list is empty")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170329100052.29505-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
2017-03-29 13:02:24 +01:00
arch Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
block blk-mq: don't complete un-started request in timeout handler 2017-03-22 08:03:35 -06:00
certs
crypto net: Work around lockdep limitation in sockets that use sockets 2017-03-09 18:23:27 -08:00
Documentation Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
drivers Revert "drm/i915: Skip execlists_dequeue() early if the list is empty" 2017-03-29 13:02:24 +01:00
firmware
fs driver core fix for 4.11-rc4 2017-03-26 11:05:42 -07:00
include Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
init Change get_random_{int,log} to use the CRNG used by /dev/urandom and 2017-03-11 09:08:47 -08:00
ipc
kernel Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
lib mm: convert generic code to 5-level paging 2017-03-09 11:48:47 -08:00
mm mm, swap: Remove WARN_ON_ONCE() in free_swap_slot() 2017-03-21 14:13:19 -07:00
net A fix for a writeback deadlock caused by a GFP_KERNEL allocation on the 2017-03-24 14:35:39 -07:00
samples
scripts Linux 4.11-rc3 2017-03-23 12:05:13 +10:00
security
sound ALSA: hda - Adding a group of pin definition to fix headset problem 2017-03-23 09:39:55 +01:00
tools Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
usr
virt KVM: arm/arm64: VGIC: Fix command handling while ITS being disabled 2017-03-07 15:44:08 +00:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
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COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS Linux 4.11-rc4 2017-03-28 17:34:19 +10:00
Makefile Linux 4.11-rc4 2017-03-26 14:15:16 -07:00
README

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.