kernel/linux.git/lib/smp_processor_id.c, branch v6.19.11

lib/smp_processor_id: Make migration check unconditional of SMP

2025-07-10T15:52:13+00:00

Commit cac5cefbade90 ("sched/smp: Make SMP unconditional") migrate_disable() even on UP builds. Commit 06ddd17521bf1 ("sched/smp: Always define is_percpu_thread() and scheduler_ipi()") made is_percpu_thread() check the affinity mask instead replying always true for UP mask. As a consequence smp_processor_id() now complains if invoked within a migrate_disable() section because is_percpu_thread() checks its mask and the migration check is left out. Make migration check unconditional of SMP. Fixes: cac5cefbade90 ("sched/smp: Make SMP unconditional") Closes: https://lore.kernel.org/oe-lkp/202507100448.6b88d6f1-lkp@intel.com Reported-by: kernel test robot Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Chen Yu Link: https://lore.kernel.org/r/20250710082748.-DPO1rjO@linutronix.de

lib/smp_processor_id: fix imbalanced instrumentation_end() call

2022-07-18T00:31:41+00:00

Currently instrumentation_end() won't be called if printk_ratelimit() returned false. Link: https://lkml.kernel.org/r/a636d8e0-ad32-5888-acac-671f7f553bb3@I-love.SAKURA.ne.jp Fixes: 126f21f0e8d46e2c ("lib/smp_processor_id: Move it into noinstr section") Signed-off-by: Tetsuo Handa Cc: Thomas Gleixner Cc: Alexandre Chartre Cc: Peter Zijlstra Signed-off-by: Andrew Morton

lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed

2021-05-19T08:51:40+00:00

is_percpu_thread() more elegantly handles SMP vs UP, and further checks the presence of PF_NO_SETAFFINITY. This lets us catch cases where check_preemption_disabled() can race with a concurrent sched_setaffinity(). Signed-off-by: Yejune Deng [Amended changelog] Signed-off-by: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@arm.com

sched: Make migrate_disable/enable() independent of RT

2020-11-24T10:25:44+00:00

Now that the scheduler can deal with migrate disable properly, there is no real compelling reason to make it only available for RT. There are quite some code pathes which needlessly disable preemption in order to prevent migration and some constructs like kmap_atomic() enforce it implicitly. Making it available independent of RT allows to provide a preemptible variant of kmap_atomic() and makes the code more consistent in general. Signed-off-by: Thomas Gleixner Grudgingly-Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20201118204007.269943012@linutronix.de

sched: Add migrate_disable()

2020-11-10T17:38:59+00:00

Add the base migrate_disable() support (under protest). While migrate_disable() is (currently) required for PREEMPT_RT, it is also one of the biggest flaws in the system. Notably this is just the base implementation, it is broken vs sched_setaffinity() and hotplug, both solved in additional patches for ease of review. Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Daniel Bristot de Oliveira Link: https://lkml.kernel.org/r/20201023102346.818170844@infradead.org

lib/smp_processor_id: Move it into noinstr section

2020-06-11T13:14:36+00:00

That code is already not traceable. Move it into the noinstr section so the objtool section validation does not trigger. Annotate the warning code as "safe". While it might be not under all circumstances, getting the information out is important enough. Should this ever trigger from the sensitive code which is shielded against instrumentation, e.g. low level entry, then the printk is the least of the worries. Addresses the objtool warnings: vmlinux.o: warning: objtool: context_tracking_recursion_enter()+0x7: call to __this_cpu_preempt_check() leaves .noinstr.text section vmlinux.o: warning: objtool: __context_tracking_exit()+0x17: call to __this_cpu_preempt_check() leaves .noinstr.text section vmlinux.o: warning: objtool: __context_tracking_enter()+0x2a: call to __this_cpu_preempt_check() leaves .noinstr.text section Signed-off-by: Thomas Gleixner Reviewed-by: Alexandre Chartre Acked-by: Peter Zijlstra Link: https://lkml.kernel.org/r/20200505134340.902709267@linutronix.de

lib/smp_processor_id: Don't use cpumask_equal()

2019-10-09T10:46:10+00:00

The check_preemption_disabled() function uses cpumask_equal() to see if the task is bounded to the current CPU only. cpumask_equal() calls memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP, the slow memcmp() function in lib/string.c is used. On a RT kernel that call check_preemption_disabled() very frequently, below is the perf-record output of a certain microbenchmark: 42.75% 2.45% testpmd [kernel.kallsyms] [k] check_preemption_disabled 40.01% 39.97% testpmd [kernel.kallsyms] [k] memcmp We should avoid calling memcmp() in performance critical path. So the cpumask_equal() call is now replaced with an equivalent simpler check. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Juri Lelli Acked-by: Sebastian Andrzej Siewior Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Peter Zijlstra Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20191003203608.21881-1-longman@redhat.com Signed-off-by: Ingo Molnar

sched/core: Provide a pointer to the valid CPU mask

2019-06-03T09:49:37+00:00

In commit: 4b53a3412d66 ("sched/core: Remove the tsk_nr_cpus_allowed() wrapper") the tsk_nr_cpus_allowed() wrapper was removed. There was not much difference in !RT but in RT we used this to implement migrate_disable(). Within a migrate_disable() section the CPU mask is restricted to single CPU while the "normal" CPU mask remains untouched. As an alternative implementation Ingo suggested to use: struct task_struct { const cpumask_t *cpus_ptr; cpumask_t cpus_mask; }; with t->cpus_ptr = &t->cpus_mask; In -RT we then can switch the cpus_ptr to: t->cpus_ptr = &cpumask_of(task_cpu(p)); in a migration disabled region. The rules are simple: - Code that 'uses' ->cpus_allowed would use the pointer. - Code that 'modifies' ->cpus_allowed would use the direct mask. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Linus Torvalds Cc: Peter Zijlstra Link: https://lkml.kernel.org/r/20190423142636.14347-1-bigeasy@linutronix.de Signed-off-by: Ingo Molnar

kprobes: Prohibit probing on preemption checking debug functions

2019-02-13T07:16:40+00:00

Since kprobes depends on preempt disable/enable, probing on the preempt debug routines can cause recursive breakpoint bugs. Signed-off-by: Masami Hiramatsu Cc: Alexander Shishkin Cc: Andrea Righi Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Mathieu Desnoyers Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/154998804911.31052.3541963527929117920.stgit@devbox Signed-off-by: Ingo Molnar

lib: do not use print_symbol()

2018-01-05T14:24:00+00:00

print_symbol() is a very old API that has been obsoleted by %pS format specifier in a normal printk() call. Replace print_symbol() with a direct printk("%pS") call. Link: http://lkml.kernel.org/r/20171211125025.2270-13-sergey.senozhatsky@gmail.com To: Andrew Morton To: Russell King To: Catalin Marinas To: Mark Salter To: Tony Luck To: David Howells To: Yoshinori Sato To: Guan Xuetao To: Borislav Petkov To: Greg Kroah-Hartman To: Thomas Gleixner To: Peter Zijlstra To: Vineet Gupta To: Fengguang Wu Cc: Steven Rostedt Cc: Petr Mladek Cc: LKML Cc: linux-arm-kernel@lists.infradead.org Cc: linux-c6x-dev@linux-c6x.org Cc: linux-ia64@vger.kernel.org Cc: linux-am33-list@redhat.com Cc: linux-sh@vger.kernel.org Cc: linux-edac@vger.kernel.org Cc: x86@kernel.org Cc: linux-snps-arc@lists.infradead.org Signed-off-by: Sergey Senozhatsky [pmladek@suse.com: updated commit message] Signed-off-by: Petr Mladek