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stop_machine: Make stop_one_cpu_nowait() return void

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No caller checks the return value from stop_one_cpu_nowait(). All
callers require the callback to run and arrange for the target CPU's
stopper to remain enabled while queuing the work. In particular, commit
f0498d2a54 ("sched: Fix stop_one_cpu_nowait() vs hotplug") added
preemption protection to the scheduler callers so that queuing must
succeed once the target CPU has been observed online.

Therefore, a failure is an unrecoverable violation rather than a condition
individual callers can recover from. Diagnose it with WARN_ON_ONCE() in
stop_one_cpu_nowait(). A check in the common helper covers current and
future callers consistently, while individual checks would duplicate
the same non-recoverable handling at every call site.

Make the function return void because there is no longer a meaningful
result for callers to consume.

On UP, warn if the supplied CPU is not the current CPU because the work
cannot be scheduled in that case.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bradley Morgan <include@grrlz.net>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260729022355.325058-1-ynorov@nvidia.com
This commit is contained in:
Yury Norov
2026-07-28 22:23:54 -04:00
committed by Peter Zijlstra
parent 04998aa548
commit 5186ef3690
2 changed files with 15 additions and 18 deletions
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19
include/linux/stop_machine.h
View File

@@ -2,6 +2,7 @@
#ifndef _LINUX_STOP_MACHINE
#define _LINUX_STOP_MACHINE
#include <linux/bug.h>
#include <linux/cpu.h>
#include <linux/cpumask_types.h>
#include <linux/smp.h>
@@ -31,7 +32,7 @@ struct cpu_stop_work {
int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg);
bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
struct cpu_stop_work *work_buf);
void stop_machine_park(int cpu);
void stop_machine_unpark(int cpu);
@@ -68,19 +69,17 @@ static void stop_one_cpu_nowait_workfn(struct work_struct *work)
preempt_enable();
}
static inline bool stop_one_cpu_nowait(unsigned int cpu,
static inline void stop_one_cpu_nowait(unsigned int cpu,
cpu_stop_fn_t fn, void *arg,
struct cpu_stop_work *work_buf)
{
if (cpu == smp_processor_id()) {
INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn);
work_buf->fn = fn;
work_buf->arg = arg;
schedule_work(&work_buf->work);
return true;
}
if (WARN_ON_ONCE(cpu != smp_processor_id()))
return;
return false;
INIT_WORK(&work_buf->work, stop_one_cpu_nowait_workfn);
work_buf->fn = fn;
work_buf->arg = arg;
schedule_work(&work_buf->work);
}
static inline void print_stop_info(const char *log_lvl, struct task_struct *task) { }

14
kernel/stop_machine.c
View File

@@ -7,6 +7,7 @@
* Copyright (C) 2010 SUSE Linux Products GmbH
* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
*/
#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/cpu.h>
@@ -376,17 +377,14 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *
* and will remain untouched until stopper starts executing @fn.
*
* CONTEXT:
* Don't care.
*
* RETURNS:
* true if cpu_stop_work was queued successfully and @fn will be called,
* false otherwise.
* Don't care, but the caller must ensure @cpu's stopper stays enabled
* until the work is queued, e.g. by preempt_disable().
*/
bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
struct cpu_stop_work *work_buf)
void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
struct cpu_stop_work *work_buf)
{
*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, .caller = _RET_IP_, };
return cpu_stop_queue_work(cpu, work_buf);
WARN_ON_ONCE(!cpu_stop_queue_work(cpu, work_buf));
}
static bool queue_stop_cpus_work(const struct cpumask *cpumask,