pagefault ftrace cr2 corruption

Summary

Problem: perf_fuzzer segfaulting at impossible address. It turns out the ftrace code when tracing the page fault handler would corrupt the x86 cr2 register (pagefault source address register) causing a secondary fault (to write out event data) to improperly segfault.

Found by

perf_fuzzer

Independently found later by Jiri Olsa

Fixed-by

x86, trace: Fix CR2 corruption when tracing page faults

0ac09f9f8cd1fb028a48330edba6023d347d3cea

3.14-rc6

Also: he has proposed a patch to avoid constructing user stack traces that might be related.

Linux-kernel

21 February 2014 -- perf_fuzzer causes reboot

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