lkml.org 
[lkml]   [2009]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts
From
Date
On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote:

> The equivalence of contexts is detected by keeping a pointer in
> each cloned context pointing to the context it was cloned from.
> To cope with the situation where a context is changed by adding
> or removing counters after it has been cloned, we also keep a
> generation number on each context which is incremented every time
> a context is changed. When a context is cloned we take a copy
> of the parent's generation number, and two cloned contexts are
> equivalent only if they have the same parent and the same
> generation number. In order that the parent context pointer
> remains valid (and is not reused), we increment the parent
> context's reference count for each context cloned from it.

> + u32 generation;

Suppose someone writes a malicious proglet that inherits the counters,
puts the child to sleep, does 2^32 mods on the counter set, and then
wakes up the child.

Would that merely corrupt the results, or make the kernel explode?



\
 
 \ /
  Last update: 2009-05-22 10:35    [from the cache]
©2003-2011 Jasper Spaans