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Chris Wilson 97f9af78f3 drm/i915/gt: Mark the execlists->active as the primary volatile access
Since we want to do a lockless read of the current active request, and
that request is written to by process_csb also without serialisation, we
need to instruct gcc to take care in reading the pointer itself.

Otherwise, we have observed execlists_active() to report 0x40.

[ 2400.760381] igt/para-4098    1..s. 2376479300us : process_csb: rcs0 cs-irq head=3, tail=4
[ 2400.760826] igt/para-4098    1..s. 2376479303us : process_csb: rcs0 csb[4]: status=0x00000001:0x00000000
[ 2400.761271] igt/para-4098    1..s. 2376479306us : trace_ports: rcs0: promote { b9c59:2622, b9c55:2624 }
[ 2400.761726] igt/para-4097    0d... 2376479311us : __i915_schedule: rcs0: -2147483648->3, inflight:0000000000000040, rq:ffff888208c1e940

which is impossible!

The answer is that as we keep the existing execlists->active pointing
into the array as we copy over that array, the unserialised read may see
a partial pointer value.

Fixes: df40306902 ("drm/i915/execlists: Lift process_csb() out of the irq-off spinlock")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191125094318.1630806-1-chris@chris-wilson.co.uk
(cherry picked from commit 331bf90591)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
2019-11-25 16:36:40 +02:00
arch ARM: SoC fixes 2019-11-10 13:41:59 -08:00
block blkcg: make blkcg_print_stat() print stats only for online blkgs 2019-11-06 17:08:38 -07:00
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Documentation Merge tag 'drm-next-5.5-2019-11-08' of git://people.freedesktop.org/~agd5f/linux into drm-next 2019-11-14 08:43:07 +10:00
drivers drm/i915/gt: Mark the execlists->active as the primary volatile access 2019-11-25 16:36:40 +02:00
fs configfs regression fix for 5.4-rc 2019-11-10 12:59:34 -08:00
include Merge branch 'vmwgfx-next' of git://people.freedesktop.org/~thomash/linux into drm-next 2019-11-15 12:34:45 +10:00
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kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-11-10 12:03:58 -08:00
lib lib: Remove select of inexistant GENERIC_IO 2019-11-10 10:38:43 -08:00
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mm mm: memcontrol: fix network errors from failing __GFP_ATOMIC charges 2019-11-06 08:47:50 -08:00
net vsock/virtio: fix sock refcnt holding during the shutdown 2019-11-08 12:17:50 -08:00
samples samples/bpf: fix build by setting HAVE_ATTR_TEST to zero 2019-10-31 21:39:15 +01:00
scripts Modules fixes for v5.4-rc7 2019-11-08 09:48:19 -08:00
security Linux 5.4-rc7 2019-11-14 05:53:10 +10:00
sound ASoC: Fixes for v5.4 2019-11-07 13:52:17 +01:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-11-10 11:55:53 -08:00
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MAINTAINERS Linux 5.4-rc7 2019-11-14 05:53:10 +10:00
Makefile Linux 5.4-rc7 2019-11-10 16:17:15 -08:00
README

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.