[PATCH v1 0/4] coresight: support panic dump functionality

On 5 June 2017 at 02:57, Suzuki K Poulose [off-list ref] wrote:

On 03/06/17 15:42, Leo Yan wrote:

quoted

### Introduction ###

Embedded Trace Buffer (ETB) provides on-chip storage of trace data,
usually has buffer size from 2KB to 8KB. These data has been used for
profiling and this has been well implemented in coresight driver.

This patch set is to explore ETB RAM data for postmortem debugging.
We could consider ETB RAM data is quite useful for postmortem debugging,
especially if the hardware design with local ETB buffer (ARM DDI 0461B)
chapter 1.2.7. 'Local ETF', with this kind design every CPU has one
dedicated ETB RAM. So it's quite handy that we can use alive CPU to help
dump the hang CPU ETB RAM. Then we can quickly get to know what's the
exact execution flow before its hang.

Due ETB RAM buffer has small size, if all CPUs shared one ETB buffer
then the trace data for causing error is easily to be overwritten by
other PEs; but even so sometimes we still have chance to go through the
trace data to assist debugging panic issues.

### Implementation ###

Firstly we need provide a unified APIs for panic dump functionality, so
it can be easily extended to enable panic dump for multiple drivers. This
is finished by patch 0001, it registers panic notifier, and provide the
general APIs {coresight_add_panic_cb|coresight_del_panic_cb} as helper
functions so any coresight device can add into dump list or delete itself
as needed.

Generally all the panic dump specific stuff are related to the sinks
devices, so this initial version code it only supports sink devices; and
Patch 0002 is to add and remove panic callback for sink devices.

Patch 0003 and 0004 are to add panic callback functions for tmc and etb10
drivers; so these two drivers can save specific trace data when panic
happens.

NOTE: patch 0003 for tmc driver panic callback which has been verified on
Hikey board. patch 0004 for etb10 has not been tested due lack hardware
in hand.

quoted

- After kernel panic happens, the kdump launches dump-capture kernel;
  so we need save kernel's dump file on target:
  cp /proc/vmcore ./vmcore

quoted

  After we download vmcore file from Hikey board to host PC, we can
  use 'crash' tool to check coresight dump info and extract trace data:
  crash vmlinux vmcore
  crash> log
  [   37.559337] coresight f6402000.etf: invoke panic dump...
  [   37.565460] coresight-tmc f6402000.etf: Dump ETB buffer
0x2000 at 0xffff80003b8da180
  crash> rd 0xffff80003b8da180 0x2000 -r cs_etb_trace.bin

Have you explored appending the above information as a vmcoreinfo parameter
via
vmcoreinfo_append_str() ? That would make it easier to list all the
information
above and if needed, we may be able to extend the makedumpfile to dump the
ETB
dumps from a given vmcore.
 Suzuki

One thing this patchset doesn't address is the tracer configuration
(metadata).  I'm thinking we can use the same mechanism to store the
relevant information in memory in the same format done for perf.