do_undefinstr call sem down_read?

Fri Apr 25 01:57:32 PDT 2014

On Thu, Apr 24, 2014 at 04:50:25PM +0800, Alex Shi wrote:
> I caught the following issue few times on my panda board on lsk. but I
> track the code path, looks like the upstream kernel has the same problem
> too.
...
> [   30.733612] [<c0008417>] (do_undefinstr+0x10b/0x13c) from [<c050cbe3>] (__und_svc_finish+0x1/0x3e)
> [   30.743103] Exception stack(0xedd5fc50 to 0xedd5fc98)
> [   30.748443] fc40:                                     c13c14e0 80000000 00000080 00000000
> [   30.757141] fc60: c13c14e0 0000000c eac67284 c13c14e0 edc11518 c0df95c0 c0824410 eac67240
> [   30.765808] fc80: 00000000 edd5fcd8 c00171f9 c00cf998 80000133 ffffffff
> [   30.772827] [<c050cbe3>] (__und_svc_finish+0x1/0x3e) from [<c00cf998>] (page_mapping+0x20/0x38)
> [   30.782073] [<c00cf998>] (page_mapping+0x20/0x38) from [<c00171f9>] (flush_dcache_page+0x1d/0x60)

The real question is why is page_mapping triggering an undefined
instruction exception.  That I have no answer for.

This function is a hot path, so I doubt that it really is an undefined
instruction.  I suspect either your CPU has an erratum, or you have
hardware problems.

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