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    SubjectRe: BUG: Global FPU corruption in 2.2
    On Thu, Apr 19, 2001 at 11:05:03AM -0500, Victor Zandy wrote:
    > We have found that one of our programs can cause system-wide
    > corruption of the x86 FPU under 2.2.16 and 2.2.17.
    > We see this problem on dual 550MHz Xeons with 1GB RAM.

    Hm, I started to wonder if this is not somewhat related to a recent
    report I got. "The victim" was running 2.2.19 (basically) on an SMP
    Alpha UP2000+ with two 800 MHz processors. He managed to reduce the
    problem to a rather small test case and I attach sources, Makefile and
    a "" driver as a shar archive if you want to have a closer look.

    This "" simply fires triplets of "harry" process in a loop.
    The guy hit by this gets apparently random floating point exceptions
    starting with roughly sixth process and later intervals between bombs
    will vary. I have also 'strace' outputs from failing processes but
    they are not telling very much. 'gdb' is also not very illuminating:

    Program received signal SIGFPE, Arithmetic exception.
    0x1200010a8 in vadd_ (a=0x11fff21e4, ia=0x120003294, b=0x11fff7004,
    ib=0x120003294, c=0x11fffbe20, ic=0x120003294, n=0x11ffffc70) at vadd.f:99
    99 C(CI) = A(AI) + B(BI)
    Current language: auto; currently fortran

    (gdb) p *ia
    $10 = 1
    (gdb) p *ib
    $11 = 1
    (gdb) p *ic
    $12 = 1
    (gdb) p *n
    Cannot access memory at address 0x4
    (gdb) p *(0x11ffffc70)
    $13 = 1024

    (gdb) info locals
    n = (PTR TO -> ( integer )) 0x4
    __g77_expr_0 = 10

    He tells me that he is getting that on two different machines he has

    The trouble is that I tried to repeat that with different hardware,
    kernels, compilers and libraries and I failed even on SMP; but I got an
    access to a box with only 667 MHz processors. OTOH he is running
    right now 2.4.3-ac9 plus Andrea Arcangeli patches for rw semaphores
    on Alpha and he reports that the problem went away (and, hopefuly,
    nothing else will crop out :-).

    Anybody can offer an insight what that may really be? It may be,
    of course, totally unrelated to this report from Victor Zandy.


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