Re: The disappearing sys_call_table export.

[Jesse Pollard <jesse@cats-chateau.net>]

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.