Re: 2.6.17-rc5-mm1

[Martin Bligh <mbligh@google.com>]

>>>Not really (though the clarity and reassurance of the additional
>>>MAX_SWAPFILES test is good).  We went over it a year or two back,
>>>and the macro contortions do involve MAX_SWAPFILES_SHIFT: which
>>>up to and including 2.6.17 has enforced the MAX_SWAPFILES limit.
>>
>>It looks though as if the testers were able to define more than 32 swap 
>>devices. So there is the danger of overwriting the memory 
>>following the swap info if we do not fix this.
>>
>>Where are the macro contortions? No arch uses MAX_SWAPFILES_SHIFT for its 
>>definitions and the only other significant use is in swapops.h to 
>>determine the shift.
> 
> 
> I'll go mad if I try to work it out again: I was as worried as you
> when I discovered that test in sys_swapon a year or so ago, apparently
> without any check on MAX_SWAPFILES; and went moaning to Andrew.  But
> once I'd worked through swp_type, pte_to_swp_entry, swp_entry_to_pte,
> swp_entry, I did come to the conclusion that the MAX_SWAPFILES bound
> was actually safely built in there.

If it's that difficult to figure out, is that not reason enough to rip
it all out and replace it? ;-) Life seems quite complicated enough as
it is.

M.