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    SubjectRe: The disappearing sys_call_table export.
    Date
    On Thursday 08 May 2003 10:29, Terje Malmedal wrote:
    > [Christoph Hellwig]
    >
    > >> The only problem I can see is that different modules overloading the
    > >> same function needs to be unloaded in the correct order. Is this the
    > >> only reason for removing it, or am I missing something?
    > >
    > > it's racy - and it doesn't work on half of the arches added over the
    > > last years.
    >
    > Would you be so kind as to explain exactly what is racy? Just
    > asserting that it is does not help me understand anything.

    Look at this:

    [1]int init_module(void)
    [2]{
    [3] orig_fsync=sys_call_table[SYS_fsync];
    [4] sys_call_table[SYS_fsync]=hacked_fsync;
    [5] return 0;
    [6]}

    Unless there is a LOCK on sys_call_table[SYS_fsync] another CPU could
    replace the pointer between lines 3 and 4. At that point line 4 would
    destroy the existing entry.. or destroy it when the original is restored,
    and would NOT be restoring the one insterted.
    -
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