backtrace: replace timer with tasklet + completions
backtrace: replace timer with tasklet + completions

On qemu, the backtrace would show up _after_ the "end of backtrace
testing" message.

This patch changes it to use completions instead, which will guarantee
that no such race exists.

Cc: Arjan van de Ven <9043bf4b08f6c93a2cb55d98c3494b123858348f@infradead.org>
Signed-off-by: Vegard Nossum <c9abf7248a519119ccb31f4fd3c3a4e0b6ebd20b@gmail.com>
Cc: Arjan van de Ven <9043bf4b08f6c93a2cb55d98c3494b123858348f@infradead.org>
Cc: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas