How to debug system freeze (not detected by kernel debug options)

[Jongman Heo <jongman.heo@samsung.com>]

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Dear kernel hackers,

I have a problem in SMP environment, in x86 platform (Intel Atom based embedded system)

In UP, there is no issue, but in SMP, system freezed in tens of minutes (or shorter), if I perform IO test with flash memory and HDD simultaneously (using dd).

I enabled relevant kernel debug options, like LOCKDEP, DETECT_SOFTLOCKUP, DETECT_HUNG_TASK, along with "nmi_watchdog=1".
(Yeah, this is somewhat old kernel, 2.6.35.14).

But no debug message is shown. (I had checked that NMI interrupt count correctly increase.).

Do you have any thoughts what can cause system freeze without being detected by LOCKDEP, watchdog, and other options.

Thanks in advance,
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