Le 02/03/2018 à 20:54, Mathieu Malaterre a écrit :
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 ?
No it is fine for me.
Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>
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