From: Yury Norov yury.norov@gmail.com
mainline inclusion from mainline-v6.1-rc1 commit aa47a7c215e79a2ade6916f163c5a17b561bce4f category: cleanup bugzilla: https://gitee.com/openeuler/kernel/issues/I8KQBZ CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Cpumask code is written in assumption that when CONFIG_CPUMASK_OFFSTACK is enabled, all cpumasks have boot-time defined size, otherwise the size is always NR_CPUS.
The latter is wrong because the number of possible cpus is always calculated on boot, and it may be less than NR_CPUS.
On my 4-cpu arm64 VM the nr_cpu_ids is 4, as expected, and nr_cpumask_bits is 256, which corresponds to NR_CPUS. This not only leads to useless traversing of cpumask bits greater than 4, this also makes some cpumask routines fail.
For example, cpumask_full(0b1111000..000) would erroneously return false in the example above because tail bits in the mask are all unset.
This patch deprecates nr_cpumask_bits and wires it to nr_cpu_ids unconditionally, so that cpumask routines will not waste time traversing unused part of cpu masks. It also fixes cpumask_full() and similar routines.
As a side effect, because now a length of cpumasks is defined at run-time even if CPUMASK_OFFSTACK is disabled, compiler can't optimize corresponding functions.
It increases kernel size by ~2.5KB if OFFSTACK is off. This is addressed in the following patch.
Signed-off-by: Yury Norov yury.norov@gmail.com Signed-off-by: Zheng Zucheng zhengzucheng@huawei.com --- include/linux/cpumask.h | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index 192144b52b47..cb8f29fd0477 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -44,13 +44,8 @@ static inline void set_nr_cpu_ids(unsigned int nr) } #endif
-#ifdef CONFIG_CPUMASK_OFFSTACK -/* Assuming NR_CPUS is huge, a runtime limit is more efficient. Also, - * not all bits may be allocated. */ +/* Deprecated. Always use nr_cpu_ids. */ #define nr_cpumask_bits nr_cpu_ids -#else -#define nr_cpumask_bits ((unsigned int)NR_CPUS) -#endif
/* * The following particular system cpumasks and operations manage