Messages in this thread | | | Date | Tue, 6 Jun 2006 18:20:39 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: 2.6.17-rc5-mm1 |
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On Tue, 6 Jun 2006, Christoph Lameter wrote: > On Tue, 6 Jun 2006, Hugh Dickins wrote: > > > 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.
It's those four in swapops.h, and their concatenation in sys_swapon, that I meant by "macro contortions"; and I think they are safe (or were prior to swapless migration's -2), whatever the arch does for the __ones (which drive me even further insane).
Have you no mercy? Oh, wasn't it rendered safe by the:
#define SWP_TYPE_SHIFT(e) (sizeof(e.val) * 8 - MAX_SWAPFILES_SHIFT) static inline unsigned swp_type(swp_entry_t entry) { return (entry.val >> SWP_TYPE_SHIFT(entry)); }
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