Commit-ID: 427d77a32365d5f942d335248305a5c237baf63a Gitweb: http://git.kernel.org/tip/427d77a32365d5f942d335248305a5c237baf63a Author: Thomas Gleixner <[email protected]> AuthorDate: Tue, 13 Dec 2016 19:32:28 +0100 Committer: Thomas Gleixner <[email protected]> CommitDate: Thu, 15 Dec 2016 11:32:31 +0100
x86/smpboot: Prevent false positive out of bounds cpumask access warning prefill_possible_map() reinitializes the cpu_possible_map by setting the possible cpu bits and clearing all other bits up to NR_CPUS. This is technically always correct because cpu_possible_map is statically allocated and sized NR_CPUS. With CPUMASK_OFFSTACK and DEBUG_PER_CPU_MAPS enabled the bounds check of cpu masks happens on nr_cpu_ids. nr_cpu_ids is initialized to NR_CPUS and only limited after the set/clear bit loops have been executed. But if the system was booted with "nr_cpus=N" on the command line, where N is < NR_CPUS then nr_cpu_ids is limited in the parameter parsing function before prefill_possible_map() is invoked. As a consequence the cpumask bounds check triggers when clearing the bits past nr_cpu_ids. Add a helper which allows to reset cpu_possible_map w/o the bounds check and then set only the possible bits which are well inside bounds. Reported-by: Dmitry Safonov <[email protected]> Cc: Rusty Russell <[email protected]> Cc: [email protected] Cc: Jan Beulich <[email protected]> Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1612131836050.3415@nanos Signed-off-by: Thomas Gleixner <[email protected]> --- arch/x86/kernel/smpboot.c | 8 ++++---- include/linux/cpumask.h | 5 +++++ 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index e09aa58..46732dc 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1463,15 +1463,15 @@ __init void prefill_possible_map(void) possible = i; } + nr_cpu_ids = possible; + pr_info("Allowing %d CPUs, %d hotplug CPUs\n", possible, max_t(int, possible - num_processors, 0)); + reset_cpu_possible_mask(); + for (i = 0; i < possible; i++) set_cpu_possible(i, true); - for (; i < NR_CPUS; i++) - set_cpu_possible(i, false); - - nr_cpu_ids = possible; } #ifdef CONFIG_HOTPLUG_CPU diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index da7fbf1..c717f5e 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -722,6 +722,11 @@ void init_cpu_present(const struct cpumask *src); void init_cpu_possible(const struct cpumask *src); void init_cpu_online(const struct cpumask *src); +static inline void reset_cpu_possible_mask(void) +{ + bitmap_zero(cpumask_bits(&__cpu_possible_mask), NR_CPUS); +} + static inline void set_cpu_possible(unsigned int cpu, bool possible) {
