Messages in this thread | | | Date | Wed, 3 Aug 2022 11:42:11 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86/numa: Use cpumask_available instead of hardcoded NULL check |
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* Siddh Raman Pant <code@siddh.me> wrote:
> On Wed, 03 Aug 2022 14:38:19 +0530 Ingo Molnar <mingo@kernel.org> wrote: > > > > * Siddh Raman Pant <code@siddh.me> wrote: > > > There is no reason why allmodconfig would trigger the warning, [...] > > > > Well, unless I'm misreading your changelog, all the warning needs to > > trigger is CONFIG_CPUMASK_OFFSTACK=y. > > > > > as it has CONFIG_CPUMASK_OFFSTACK=y, but the warning is because of the > > > other case. > > > > What 'other case'? I've re-read the discussion and don't see it, but maybe > > I'm a bit daft this morning ... > > No, the warning is happening because CONFIG_CPUMASK_OFFSTACK is not set.
Oh. So I was daft, as suspected. ;-)
And I can confirm that while gcc-11 doesn't trigger the warning, gcc-12 does:
$ make ARCH=x86_64 CC=gcc-11 arch/x86/mm/numa.o CC arch/x86/mm/numa.o $
$ rm -f arch/x86/mm/numa.o $ $ make ARCH=x86_64 CC=gcc-12 arch/x86/mm/numa.o
CC arch/x86/mm/numa.o arch/x86/mm/numa.c: In function ‘cpumask_of_node’: arch/x86/mm/numa.c:916:39: error: the comparison will always evaluate as ‘false’ for the address of ‘node_to_cpumask_map’ will never be NULL [-Werror=address] 916 | if (node_to_cpumask_map[node] == NULL) {
> [...] This is because in that case cpumask_var_t type is not a pointer, > and thus the var can never be NULL, which leads gcc to warn us when > comparing with NULL. > > The chain of events are like: > > #ifdef CONFIG_CPUMASK_OFFSTACK > typedef struct cpumask *cpumask_var_t; > #else > typedef struct cpumask cpumask_var_t[1]; > endif > > cpumask_var_t node_to_cpumask_map[MAX_NUMNODES]; > ... > if (node_to_cpumask_map[node] == NULL) { > > > The fix works because: > > #ifdef CONFIG_CPUMASK_OFFSTACK > static inline bool cpumask_available(cpumask_var_t mask) > { > return mask != NULL; > } > #else > static inline bool cpumask_available(cpumask_var_t mask) > { > return true; > } > endif > > > The conditional definitions, as pointed out earlier, can be seen from line 700 > of include/linux/cpumask.h file.
Yeah - and I agree with your fix - will apply it.
Thanks for your patience :-)
Ingo
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