CVE request -- kernel: perf: fix software event overflow

[Petr Matousek <pmatouse () redhat com>]

Hello Steve, vendors.

Description:
Under certain circumstances software event overflows go wrong and
deadlock. Avoid trying to delete a timer from the timer callback.

References:
https://bugzilla.redhat.com/show_bug.cgi?id=730706
https://lkml.org/lkml/2011/7/27/337 (reproducer)
https://lkml.org/lkml/2011/7/28/284 (fix)

Upstream fix:
a8b0ca17b80e92faab46ee7179ba9e99ccb61233 (much larger patch that
contains the hunk referenced above)

Thank you,
-- 
Petr Matousek / Red Hat Security Response Team