Re: Something very strange on x86_64 2.6.X kernels

[Eric Dumazet]

Andrew Morton wrote:

> Eric Dumazet <dada1@xxxxxxxxxxxxx> wrote:

> > Every time the crash occurs when one thread is using some ram located at 
> > virtual address 0xffffe6xx
>
>
> What does "using" mean?  Is the program executing from that location?

No, the program text is located between 0x00100000 and 0x001c6000  (no 
shared libs)

0xffffe6xx is READ|WRITE data, mapped on Hugetlb fs

extract from /proc/pid/maps
ff400000-100400000 rw-s 82000000 00:0b 12960938 
   /huge/file

> Interesting.  IIRC, opterons will very occasionally (and incorrectly) take
> a fault when performing a prefetch against a dud pointer.  The kernel will
> fix that up.  At a guess, I'd say tha the fixup code isn't doing the right
> thing when the faulting EIP is in the vsyscall page.

Maybe, but I want to say that in this case, the address 'prefetched' is 
valid (ie mapped read/write by the program, on a huge page too)

Thanks
Eric Dumazet

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