drm/i915/gt: Protect defer_request() from new waiters
Mika spotted
<4>[17436.705441] general protection fault: 0000 [#1] PREEMPT SMP PTI
<4>[17436.705447] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.5.0+ #1
<4>[17436.705449] Hardware name: System manufacturer System Product Name/Z170M-PLUS, BIOS 3805 05/16/2018
<4>[17436.705512] RIP: 0010:__execlists_submission_tasklet+0xc4d/0x16e0 [i915]
<4>[17436.705516] Code: c5 4c 8d 60 e0 75 17 e9 8c 07 00 00 49 8b 44 24 20 49 39 c5 4c 8d 60 e0 0f 84 7a 07 00 00 49 8b 5c 24 08 49 8b 87 80 00 00 00 <48> 39 83 d8 fe ff ff 75 d9 48 8b 83 88 fe ff ff a8 01 0f 84 b6 05
<4>[17436.705518] RSP: 0018:
ffffc9000012ce80 EFLAGS:
00010083
<4>[17436.705521] RAX:
ffff88822ae42000 RBX:
5a5a5a5a5a5a5a5a RCX:
dead000000000122
<4>[17436.705523] RDX:
ffff88822ae42588 RSI:
ffff8881e32a7908 RDI:
ffff8881c429fd48
<4>[17436.705525] RBP:
ffffc9000012cf00 R08:
ffff88822ae42588 R09:
00000000fffffffe
<4>[17436.705527] R10:
ffff8881c429fb80 R11:
00000000a677cf08 R12:
ffff8881c42a0aa8
<4>[17436.705529] R13:
ffff8881c429fd38 R14:
ffff88822ae42588 R15:
ffff8881c429fb80
<4>[17436.705532] FS:
0000000000000000(0000) GS:
ffff88822ed00000(0000) knlGS:
0000000000000000
<4>[17436.705534] CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
<4>[17436.705536] CR2:
00007f858c76d000 CR3:
0000000005610003 CR4:
00000000003606e0
<4>[17436.705538] DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
<4>[17436.705540] DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
<4>[17436.705542] Call Trace:
<4>[17436.705545] <IRQ>
<4>[17436.705603] execlists_submission_tasklet+0xc0/0x130 [i915]
which is us consuming a partially initialised new waiter in
defer_requests(). We can prevent this by initialising the i915_dependency
prior to making it visible, and since we are using a concurrent
list_add/iterator mark them up to the compiler.
Fixes:
8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200206204915.2636606-2-chris@chris-wilson.co.uk
(cherry picked from commit
f14f27b1663269a81ed62d3961fe70250a1a0623)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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