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Re: [RFC][PATCH]Atomically insert/remove probes
- From: Prasanna S Panchamukhi <prasanna at in dot ibm dot com>
- To: anil dot s dot keshavamurthy at intel dot com
- Cc: systemtap at sources dot redhat dot com
- Date: Wed, 25 May 2005 18:42:03 +0530
- Subject: Re: [RFC][PATCH]Atomically insert/remove probes
- Reply-to: prasanna at in dot ibm dot com
Hi Anil,
> On many architecture it is not architecturally possible to atomically
>insert or remove a probe as the size of the instruction to be patched
>might exceed the atomic width of that architecture. Hence there is
>alway a race condition where in, cpuN while inserting/removing a probe at some
>address, cpuM might be reading/executing at the same address. In this
>case, cpuM if it see's old instruction then there is no issuess, but if
>it reads/executes the incompletely updated instruction, then this might trigger
>all sorts of uncertainty as the instruction which cpuM is executing could
>vary from random instruction to illegal instruction.
Probably this case might be true in IA-64, but I cannot think of such a
situation on intel i386 and x86_64 architecture. If you have a test case,
could you please post it.
Thanks
Prasanna
--
Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@in.ibm.com>