Re: v3.13-rc6+ regression (ARM board)

From: Krzysztof HaÅasa
Date: Thu Jan 02 2014 - 05:03:07 EST

>> There seems to be a regression in v3.13-rc6+ (up to current tip =
>> 71ce176ee6ed1735b9a1160a5704a915d13849b1).
>> Board is Gateworks Cambria, CPU Intel IXP435 ARM big endian, gcc 4.7.3.
>> The board boots correctly and works (shell mostly, and SSHD) for about
>> 50 seconds. After 52-54 seconds, it frozes dead without any console
>> (UART) output.
>> Bisecting shows 5e30025a319910695f5010dc0fb53a23299da14d as the first
>> bad commit. Interestingly it's a merge:

Reverting 1ca7d67cf5d5a2aef26a8d9afd789006fa098347 on top of current tip
(9a0bb2966efbf30a71c128c3af63307d8b5f5fc0) fixes my issue.

What now?

seqcount: Add lockdep functionality to seqcount/seqlock structures

Currently seqlocks and seqcounts don't support lockdep.

After running across a seqcount related deadlock in the timekeeping
code, I used a less-refined and more focused variant of this patch
to narrow down the cause of the issue.

This is a first-pass attempt to properly enable lockdep functionality
on seqlocks and seqcounts.

Since seqcounts are used in the vdso gettimeofday code, I've provided
non-lockdep accessors for those needs.

I've also handled one case where there were nested seqlock writers
and there may be more edge cases.

Comments and feedback would be appreciated!
Krzysztof Halasa

Research Institute for Automation and Measurements PIAP
Al. Jerozolimskie 202, 02-486 Warsaw, Poland
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