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https://github.com/linux-msm/laptops-kernel.git
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Chuyi ZhouandThomas Gleixner
0485235b6e
smp_call_function_any() disables preemption across the entire operation: selecting a target CPU, enqueueing the IPI, and synchronously waiting for the remote CPU. smp_call_function_single() already re-enables preemption before the synchronous csd_lock_wait(), so callers of smp_call_function_any() should benefit from the same shorter preemption-disabled section. Simply removing get_cpu() and put_cpu() from smp_call_function_any() would leave the preemption disablement entirely to smp_call_function_single(). That opens a preemption window between selecting the remote CPU, for example via sched_numa_find_nth_cpu(), and dispatching the IPI in smp_call_function_single(). If the selected CPU is fully offlined in that window, smp_call_function_single() fails its cpu_online() check and returns -ENXIO to the caller, violating the guarantee that smp_call_function_any() executes on any online CPU in the mask. Move the remote CPU selection into a common __smp_call_function_single() helper. Keep the target CPU selection and IPI dispatch within the same preemption-disabled region, while still allowing the wait path to use the shorter preemption-disabled section provided by smp_call_function_single(). Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com> Signed-off-by: Thomas Gleixner <tglx@kernel.org> Tested-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://patch.msgid.link/20260709122933.4021501-4-zhouchuyi@bytedance.com
73 lines
1.5 KiB
C
73 lines
1.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Uniprocessor-only support functions. The counterpart to kernel/smp.c
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*/
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#include <linux/interrupt.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/smp.h>
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#include <linux/hypervisor.h>
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int smp_call_function_single(int cpu, void (*func)(void *info), void *info, bool wait)
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{
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unsigned long flags;
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if (cpu != 0)
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return -ENXIO;
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local_irq_save(flags);
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func(info);
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local_irq_restore(flags);
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return 0;
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}
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EXPORT_SYMBOL(smp_call_function_single);
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int smp_call_function_single_async(int cpu, call_single_data_t *csd)
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{
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unsigned long flags;
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local_irq_save(flags);
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csd->func(csd->info);
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local_irq_restore(flags);
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return 0;
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}
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EXPORT_SYMBOL(smp_call_function_single_async);
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/*
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* Preemption is disabled here to make sure the cond_func is called under the
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* same conditions in UP and SMP.
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*/
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void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
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void *info, bool wait, const struct cpumask *mask)
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{
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unsigned long flags;
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preempt_disable();
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if ((!cond_func || cond_func(0, info)) && cpumask_test_cpu(0, mask)) {
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local_irq_save(flags);
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func(info);
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local_irq_restore(flags);
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}
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preempt_enable();
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}
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EXPORT_SYMBOL(on_each_cpu_cond_mask);
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int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys)
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{
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int ret;
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if (cpu != 0)
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return -ENXIO;
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if (phys)
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hypervisor_pin_vcpu(0);
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ret = func(par);
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if (phys)
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hypervisor_pin_vcpu(-1);
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return ret;
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}
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EXPORT_SYMBOL_GPL(smp_call_on_cpu);
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