Messages in this thread |  | | Date | Mon, 9 Apr 2018 19:00:36 +0200 (CEST) | From | Sebastian Ott <> | Subject | Re: [bisected] 3c8ba0d61d04ced9f8d9ff93977995a9e4e96e91 oopses on s390 |
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On Mon, 9 Apr 2018, Sebastian Ott wrote: > On Fri, 6 Apr 2018, Kees Cook wrote: > > On Fri, Apr 6, 2018 at 2:47 AM, Sebastian Ott <sebott@linux.vnet.ibm.com> wrote: > > > Today's kernel oopsed on s390. Bisect points to: > > > 3c8ba0d61d04 ("kernel.h: Retain constant expression output for max()/min()") > > > > > > [ 1.898277] dasd-eckd 0.0.3304: DASD with 4 KB/block, 21636720 KB total size, 48 KB/track, compatible disk layout > > > [ 1.898308] ------------[ cut here ]------------ > > > [ 1.898310] kernel BUG at block/bio.c:1798! > > > > Well that's extremely bad. :( > > What happened is that the bio build by the partition detection code was > attempted to be split by the block layer because the block queue had a > max_sector setting of 0. blk_queue_max_hw_sectors uses min_not_zero. > > Both of the following return 0 on my machine: > + pr_warn("%u\n", min_not_zero(100, 1000)); > + pr_warn("%u\n", min_not_zero(1000, 100)); > > So, we now know what failed...the question is why?
I copied these macros to a userspace program to easily test it on other machines/compilers. ....maybe I did something wrong but min_not_zero did not work - even on fedora on an x86 laptop.
Sebastian#include <stdio.h>
#define __typecheck(x, y) \ (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
#define __is_constexpr(x) \ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
#define __no_side_effects(x, y) \ (__is_constexpr(x) && __is_constexpr(y))
#define __safe_cmp(x, y) \ (__typecheck(x, y) && __no_side_effects(x, y))
#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
#define __cmp_once(x, y, op) ({ \ typeof(x) __x = (x); \ typeof(y) __y = (y); \ __cmp(__x, __y, op); })
#define __careful_cmp(x, y, op) \ __builtin_choose_expr(__safe_cmp(x, y), \ __cmp(x, y, op), __cmp_once(x, y, op))
#define min(x, y) __careful_cmp(x, y, <) #define max(x, y) __careful_cmp(x, y, >)
#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <) #define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
#define min_not_zero(x, y) ({ \ typeof(x) __x = (x); \ typeof(y) __y = (y); \ __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
int main() { printf("test %u\n", min_not_zero(100, 1000)); return 0; }
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