Created attachment 96761 [details]
dmesg

System Environment:
--------------------------
Platform: ILK
kernel:   (drm-intel-nightly)1e64f527329663d8dd82f30ff5f5d01cb2407dae

Bug detailed description:
---------------------------
igt/gem_concurrent_blit/prw-overwrite-source-interruptible caused system hung or Call trace sometimes, sometimes the case is able to pass.

I tried twice on each branch(-fixes and -next-queued), didn't find this issue.

the failed rate is about 3 out of 10.

output while CallTrace occurs on -nightly kernel:
[root@x-t410b tests]# ./gem_concurrent_blit --run-subtest prw-overwrite-source-interruptible
IGT-Version: 1.6-g4fdca96 (i686) (Linux: 3.14.0_drm-intel-nightly_346aad_20140401+ i686)
using 2x512 buffers, each 1MiB
Subtest prw-overwrite-source-interruptible: SUCCESS

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.103640] CPU: 0 PID: 10078 Comm: gem_concurrent_ Not tainted 3.14.0_drm-intel-nightly_346aad_20140401+ #1223

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.103716] Hardware name: LENOVO 25222AU/25222AU, BIOS 6IET52WW (1.12 ) 02/16/2010

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.103773] task: e97334f0 ti: c2998000 task.ti: c2998000

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.105884] Stack:

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.105890] Call Trace:

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.106012] Code: 10 c7 43 28 00 01 10 00 c7 43 2c 00 02 20 00 c7 43 24 00 00 00 00 80 46 08 01 8b 43 10 85 c0 74 19 8b 50 14 85 d2 74 12 8b 52 08 <8b> 52 1c 80 7a 10 05 76 06 f0 83 28 01 74 09 89 d8 5b 5e e9 c2

Message from syslogd@x-t410b at Apr  2 10:29:11 ...
 kernel:[ 4822.106024] EIP: [<f845037f>] i915_gem_free_request+0x61/0x80 [i915] SS:ESP 0068:c2999da8

CallTrace
--------------------
[ 4822.102785] BUG: unable to handle kernel NULL pointer dereference at 0000001c
[ 4822.102857] IP: [<f845037f>] i915_gem_free_request+0x61/0x80 [i915]
[ 4822.102927] *pde = 00000000
[ 4822.102957] Oops: 0000 [#1] SMP
[ 4822.102999] Modules linked in: ip6table_filter ip6_tables ebtable_nat ebtables nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ipt_REJECT iptable_mangle xt_tcpudp iptable_filter ip_tables x_tables bridge stp llc ipv6 dm_mod iTCO_wdt iTCO_vendor_support snd_hda_codec_hdmi pcspkr joydev i2c_i801 snd_hda_codec_conexant snd_hda_codec_generic lpc_ich mfd_core firewire_ohci snd_hda_intel firewire_core snd_hda_codec crc_itu_t snd_hwdep snd_pcm snd_timer thinkpad_acpi tpm_tis tpm snd battery soundcore ac rfkill ppdev parport_pc parport wmi acpi_cpufreq i915 video button drm_kms_helper drm
[ 4822.103640] CPU: 0 PID: 10078 Comm: gem_concurrent_ Not tainted 3.14.0_drm-intel-nightly_346aad_20140401+ #1223
[ 4822.103716] Hardware name: LENOVO 25222AU/25222AU, BIOS 6IET52WW (1.12 ) 02/16/2010
[ 4822.103773] task: e97334f0 ti: c2998000 task.ti: c2998000
[ 4822.103816] EIP: 0060:[<f845037f>] EFLAGS: 00210282 CPU: 0
[ 4822.103870] EIP is at i915_gem_free_request+0x61/0x80 [i915]
[ 4822.103916] EAX: e9460e00 EBX: c78b2e00 ECX: f5fbce00 EDX: 00000000
[ 4822.103966] ESI: 00000000 EDI: f5fbce08 EBP: f5fbce00 ESP: c2999da8
[ 4822.105883]  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[ 4822.105884] CR0: 80050033 CR2: 0000001c CR3: 35993000 CR4: 000007d0
[ 4822.105884] Stack:
[ 4822.105887]  f5fbcd60 001e4e3a f84515b0 d1dd1d00 00000000 f5fbcd60 f5fbce74 f84519fc
[ 4822.105888]  00000000 f5a58300 d1dd1d00 f844cf7a 00000001 00000001 00000000 d1dd1d00
[ 4822.105890]  f5fbc000 00000000 00000000 e98d12e0 0047a000 c2999e98 e9460a00 c78b24c0
[ 4822.105890] Call Trace:
[ 4822.105907]  [<f84515b0>] ? i915_gem_retire_requests_ring+0x52/0x78 [i915]
[ 4822.105919]  [<f84519fc>] ? i915_gem_object_wait_rendering+0x37/0x4b [i915]
[ 4822.105931]  [<f844cf7a>] ? i915_gem_do_execbuffer.isra.15+0xa6a/0xedc [i915]
[ 4822.105943]  [<f844d947>] ? i915_gem_execbuffer2+0x127/0x1bc [i915]
[ 4822.105954]  [<f844d820>] ? i915_gem_execbuffer+0x434/0x434 [i915]
[ 4822.105961]  [<f813d830>] ? drm_ioctl+0x230/0x324 [drm]
[ 4822.105973]  [<f844d820>] ? i915_gem_execbuffer+0x434/0x434 [i915]
[ 4822.105977]  [<c10afde8>] ? free_pages_and_swap_cache+0x5e/0x6c
[ 4822.105980]  [<c10a3c79>] ? tlb_flush_mmu+0x43/0x57
[ 4822.105982]  [<c10a3c96>] ? tlb_finish_mmu+0x9/0x27
[ 4822.105983]  [<c10a7e4a>] ? unmap_region+0x99/0xa1
[ 4822.105989]  [<f813d600>] ? drm_core_reclaim_buffers+0x52/0x52 [drm]
[ 4822.105991]  [<c10c7a53>] ? do_vfs_ioctl+0x3f8/0x442
[ 4822.105994]  [<c1036a01>] ? do_sigaction+0xec/0x15f
[ 4822.105995]  [<c1036c56>] ? SyS_rt_sigaction+0x6f/0x7b
[ 4822.105997]  [<c10c7adf>] ? SyS_ioctl+0x42/0x6b
[ 4822.106000]  [<c169f5da>] ? sysenter_do_call+0x12/0x22
[ 4822.106012] Code: 10 c7 43 28 00 01 10 00 c7 43 2c 00 02 20 00 c7 43 24 00 00 00 00 80 46 08 01 8b 43 10 85 c0 74 19 8b 50 14 85 d2 74 12 8b 52 08 <8b> 52 1c 80 7a 10 05 76 06 f0 83 28 01 74 09 89 d8 5b 5e e9 c2
[ 4822.106024] EIP: [<f845037f>] i915_gem_free_request+0x61/0x80 [i915] SS:ESP 0068:c2999da8
[ 4822.106024] CR2: 000000000000001c
[ 4822.106054] ---[ end trace f1f562f7a5d2390d ]---

Reproduce steps:
---------------------------- 
1.  ./gem_concurrent_blit --run-subtest prw-overwrite-source-interruptible