[Bug kprobes/1971] New: Unregister race in RCU kprobes

[anil dot s dot keshavamurthy at intel dot com]

When registering a second kprobe at the same address as the first kprobe
(Multiple kprobes at the same address), add_aggr_kprobe() gets called. In 
add_aggr_kprobe() we delete the first kprobe element from the *hash list* and
add the aggregate kprobe structure to the hash list(the first kprobe structure 
is linked to aggregate kprobe) 
During this process of swapping, their is a small window in which their is 
*no* associated kprobe for that particular address. 

If during this small window, if other cpu in kprobe_handler() code, calls 
get_kprobe() for that particular address, then get_kprobe() returns null and 
their by we handle our probe incorrectly leading the system to crash.

-- 
           Summary: Unregister race in RCU kprobes
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: kprobes
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: anil dot s dot keshavamurthy at intel dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=1971

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