[Bug kprobes/2637] skipped probes in FC6

["anil dot s dot keshavamurthy at intel dot com" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From anil dot s dot keshavamurthy at intel dot com  2006-05-05 21:33 -------
> True. But such situations have in the past been extremely rare. What is
> it about the new kprobes that makes it now so common and predictable? We
> need to understand this better. 

In the past, we did not had the fixup_exception() call from 
kprobes_exception_handler() code path and due to which any page_fault 
generated by accessing user_data from pre/post handler used to
fall back to do_page_fault() function and hence you were 
not seeing failure that often. 

Again when we fall back to do_page_fault() function 
we will technically be in preempt_disable() state which 
is also wrong and potentially we could see a hang  the system
on UP system.

Hence the right thing to do here is to catch that page_fault exceptions and
try fixing up the exceptions without falling back on do_page_fault() code path.
With this simple fix, you would now experience any copy_from_user() calls from
pre/post hanlder to fail if that page is not in memory.


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http://sourceware.org/bugzilla/show_bug.cgi?id=2637

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