[Intel-gfx] [PATCH] drm/i915: Fix a use-after-free in intel_execlists_retire_requests

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5684
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  353/353              353/353
ILK                                  200/200              200/200
SNB                                  400/422              400/422
IVB              +2                 485/487              487/487
BYT                                  296/296              296/296
HSW              +1                 507/508              508/508
BDW                 -2              401/402              399/402
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 IVB  igt_gem_pwrite_pread_snooped-pwrite-blt-cpu_mmap-performance      DMESG_WARN(6, M34M21)PASS(8, M4M34)      PASS(1, M4)
 IVB  igt_gem_storedw_batches_loop_normal      DMESG_WARN(5, M34M4)PASS(15, M34M4M21)      PASS(1, M4)
 HSW  igt_gem_pwrite_pread_snooped-pwrite-blt-cpu_mmap-performance      DMESG_WARN(1, M40)PASS(18, M40M20)      PASS(1, M20)
 BDW  igt_gem_pwrite_pread_display-pwrite-blt-gtt_mmap-performance      DMESG_WARN(4, M28)PASS(2, M30)      DMESG_WARN(1, M28)
*BDW  igt_gem_pwrite_pread_uncached-pwrite-blt-gtt_mmap-performance      PASS(6, M30M28)      DMESG_WARN(1, M28)
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