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Hi Alan, On Wed, Sep 20, 2006 at 01:08:45AM +0100, Alan Cox wrote: > Ar Maw, 2006-09-19 am 13:54 -0400, ysgrifennodd Mathieu Desnoyers: > > Very good idea.. However, overwriting the second instruction with a jump could > > be dangerous on preemptible and SMP kernels, because we never know if a thread > > has an IP in any of its contexts that would return exactly at the middle of the > > jump. > > No: on x86 it is the *same* case for all of these even writing an int3. > One byte or a megabyte, > > You MUST ensure that every CPU executes a serializing instruction before > it hits code that was modified by another processor. Otherwise you get > CPU errata and the CPU produces results which vendors like to describe > as "undefined". Are you referring to Intel erratum "unsynchronized cross-modifying code" - where it refers to the practice of modifying code on one processor where another has prefetched the unmodified version of the code. Thanks Prasanna > > Thus you have to serialize, and if you are serializing it really doesn't > matter if you write a byte, a paragraph or a page. > -- Prasanna S.P. Linux Technology Center India Software Labs, IBM Bangalore Email: prasanna@in.ibm.com Ph: 91-80-41776329 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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