On Mon, Feb 26, 2018 at 9:46 AM, Segher Boessenkool <seg...@kernel.crashing.org> wrote: > On Mon, Feb 26, 2018 at 07:32:03AM +0100, Christophe LEROY wrote: >> Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit : >> >-#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < >> >max_mapnr) >> >+#define pfn_valid(pfn) \ >> >+ (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET)) >> >> What will happen when ARCH_PFN_OFFSET is not nul and pfn is lower than >> ARCH_PFN_OFFSET ? > > It will work fine. > > Say you are asking for a <= x < b so (in actual integers, no overflow) > that is 0 <= x-a < b-a and you also assume x-a overflows, so that we > are actually comparing x-a+M < b-a with M = 2**32 or such (the maximum > value in the unsigned integer type plus one). This comparison is > obviously always false. > > (It also works if b < a btw). > > Thanks Segher !
Christophe does that clarify things or do you want me to update the commit message ?
