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| author | Chris Wilson <chris@chris-wilson.co.uk> | 2019-11-25 12:43:18 +0300 |
|---|---|---|
| committer | Joonas Lahtinen <joonas.lahtinen@linux.intel.com> | 2019-11-25 17:36:40 +0300 |
| commit | 97f9af78f38d43cd058cfd40220647be67aca9f7 (patch) | |
| tree | da29df02c0975f90d9aac52d72d4ef525db3d1e1 /drivers/gpu/drm/i915/i915_syncmap.h | |
| parent | bf201f5eda23eb57f7217d20ea3e18da8cbcf52b (diff) | |
| download | linux-97f9af78f38d43cd058cfd40220647be67aca9f7.tar.xz | |
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: df403069029d ("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 331bf90591573dfe6c8e892239713ef9702f1396)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Diffstat (limited to 'drivers/gpu/drm/i915/i915_syncmap.h')
0 files changed, 0 insertions, 0 deletions