Quoting Chris Wilson (2017-11-09 14:30:19)
> Trying to enable printk debugging for GEM is fraught with the issue of
> spam; interactions with HW are very frequent and often boring. However,
> one instance where they are not so boring is just before a BUG; here
> ftrace provides a facility to dump its ringbuffer on an oops. So for CI
> let's enable trace_printk() to capture the last exchanges with HW as a
> death rattle.
>
> For example,
> [ 79.234110] ------------[ cut here ]------------
> [ 79.234137] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:907!
> [ 79.234145] invalid opcode: 0000 [#1] SMP
> [ 79.234153] Dumping ftrace buffer:
> [ 79.234158] ---------------------------------
> ...
> [ 79.314044] gem_conc-1059 1..s1 79203443us : intel_lrc_irq_handler: bcs0 out[0]: ctx=5.2, seqno=145
> [ 79.314089] gem_conc-1059 1..s. 79220800us : intel_lrc_irq_handler: bcs0 csb[1/1]: status=0x00000018:0x00000005
> [ 79.314133] gem_conc-1059 1..s. 79220803us : intel_lrc_irq_handler: bcs0 out[0]: ctx=5.1, seqno=145
> [ 79.314177] gem_conc-1062 2..s1 79230458us : intel_lrc_irq_handler: bcs0 in[0]: ctx=8.1, seqno=146
> [ 79.314220] gem_conc-1062 2..s1 79230515us : intel_lrc_irq_handler: bcs0 in[0]: ctx=8.2, seqno=147
> [ 79.314265] gem_conc-1059 1..s1 79230951us : intel_lrc_irq_handler: bcs0 csb[2/3]: status=0x00000012:0x00000008
> [ 79.314309] gem_conc-1059 1..s1 79230954us : intel_lrc_irq_handler: bcs0 out[0]: ctx=8.2, seqno=147
> [ 79.314353] gem_conc-1059 1..s1 79230954us : intel_lrc_irq_handler: bcs0 csb[3/3]: status=0x00008002:0x00000008
> [ 79.314396] gem_conc-1059 1..s1 79230955us : intel_lrc_irq_handler: bcs0 out[0]: ctx=8.1, seqno=147
> [ 79.314402] ---------------------------------
>
> v2: Tweak the formatting to be more consistent between in/out.
> v3: do {} while (0) stub macro protection
I should include a
Suggested-by: Michał Winiarski <michal.winiarski@xxxxxxxxx>
as the idea that we can use trace_printk for oops debugging came from him.
-Chris
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