Messages in this thread | | | Date | Fri, 5 Dec 2014 14:50:14 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] kernel: sysctl: use 'unsigned long' type for 'zero' variable |
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On Thu, 04 Dec 2014 07:12:45 +0100 Manfred Spraul <manfred@colorfullife.com> wrote:
> Hi Andrew, > > On 12/04/2014 12:25 AM, Andrew Morton wrote: > > On Wed, 03 Dec 2014 15:41:21 +0300 Andrey Ryabinin <a.ryabinin@samsung.com> wrote: > > > >> Use the 'unsigned long' type for 'zero' variable to fix this. > >> Changing type to 'unsigned long' shouldn't affect any other users > >> of this variable. > >> > >> Reported-by: Dmitry Vyukov <dvyukov@google.com> > >> Fixes: ed4d4902ebdd ("mm, hugetlb: remove hugetlb_zero and hugetlb_infinity") > >> Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com> > >> --- > >> kernel/sysctl.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c > >> index 15f2511..45c45c9 100644 > >> --- a/kernel/sysctl.c > >> +++ b/kernel/sysctl.c > >> @@ -120,7 +120,7 @@ static int sixty = 60; > >> > >> static int __maybe_unused neg_one = -1; > >> > >> -static int zero; > >> +static unsigned long zero; > >> static int __maybe_unused one = 1; > >> static int __maybe_unused two = 2; > >> static int __maybe_unused four = 4; > > Yeah, this is ghastly. > > > > Look at > > > > { > > .procname = "numa_balancing", > > .data = NULL, /* filled in by handler */ > > .maxlen = sizeof(unsigned int), > > .mode = 0644, > > .proc_handler = sysctl_numa_balancing, > > .extra1 = &zero, > > .extra2 = &one, > > }, > > > > Now extra1 points at a long and extra2 points at an int. > > sysctl_numa_balancing() calls proc_dointvec_minmax() and I think your > > patch just broke big-endian 64-bit machines. "sched_autogroup_enabled" > > breaks as well. > What about getting rid of "extra1" and "extra2" as well and replace it > with "min" and "max"? > > I've attached an idea
Looks sane.
> > and change proc_dointvec_minmax() and a million other functions to take > > `union sysctl_payload *' arguments. But I haven't thought about it much. > Another idea: why do we pass "int *" instead of "int"? > > With "int", we could use > .int_min = 0; > .int_max = 1;
Presumably they were originally made void* so they could point at any thing at all. But I don't recall seeing extra1 and extra2 used for anything other than bounds checking on a scalar.
Problem is, these things aren't always compile-time constants. For example, pid_max_min and pid_max_max are altered at runtime.
I doubt if we need to support both ints and longs in extra1/2 - longs should be OK for range-checking int values. The signed/unsigned issue needs thinking about - there's a "neg_one" in there. If we make everything "long" then we might run into signedness/range issues for sysctls which can have large unsigned values with the top bit set: 0x8000000-0xffffffff and 0x8000000000000000 - ...
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