Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 86ef5c9a authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Ingo Molnar
Browse files

cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus() 



Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use
get_online_cpus and put_online_cpus instead as it highlights the
refcount semantics in these operations.

The new API guarantees protection against the cpu-hotplug operation, but
it doesn't guarantee serialized access to any of the local data
structures. Hence the changes needs to be reviewed.

In case of pseries_add_processor/pseries_remove_processor, use
cpu_maps_update_begin()/cpu_maps_update_done() as we're modifying the
cpu_present_map there.

Signed-off-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent d221938c

Documentation/cpu-hotplug.txt

+6 −5
Original line number Diff line number Diff line
@@ -109,12 +109,13 @@ Never use anything other than cpumask_t to represent bitmap of CPUs. 
	for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.



	#include <linux/cpu.h>

	lock_cpu_hotplug() and unlock_cpu_hotplug():

	get_online_cpus() and put_online_cpus():



The above calls are used to inhibit cpu hotplug operations. While holding the

cpucontrol mutex, cpu_online_map will not change. If you merely need to avoid

cpus going away, you could also use preempt_disable() and preempt_enable()

for those sections. Just remember the critical section cannot call any

The above calls are used to inhibit cpu hotplug operations. While the

cpu_hotplug.refcount is non zero, the cpu_online_map will not change.

If you merely need to avoid cpus going away, you could also use

preempt_disable() and preempt_enable() for those sections.

Just remember the critical section cannot call any

function that can sleep or schedule this process away. The preempt_disable()

will work as long as stop_machine_run() is used to take a cpu down.

arch/mips/kernel/mips-mt-fpaff.c

+5 −5
Original line number Diff line number Diff line
@@ -58,13 +58,13 @@ asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len, 
	if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask)))

		return -EFAULT;



	lock_cpu_hotplug();

	get_online_cpus();

	read_lock(&tasklist_lock);



	p = find_process_by_pid(pid);

	if (!p) {

		read_unlock(&tasklist_lock);

		unlock_cpu_hotplug();

		put_online_cpus();

		return -ESRCH;

	}
@@ -106,7 +106,7 @@ asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len, 


out_unlock:

	put_task_struct(p);

	unlock_cpu_hotplug();

	put_online_cpus();

	return retval;

}
@@ -125,7 +125,7 @@ asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len, 
	if (len < real_len)

		return -EINVAL;



	lock_cpu_hotplug();

	get_online_cpus();

	read_lock(&tasklist_lock);



	retval = -ESRCH;
@@ -140,7 +140,7 @@ asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len, 


out_unlock:

	read_unlock(&tasklist_lock);

	unlock_cpu_hotplug();

	put_online_cpus();

	if (retval)

		return retval;

	if (copy_to_user(user_mask_ptr, &mask, real_len))

arch/powerpc/platforms/pseries/hotplug-cpu.c

+4 −4
Original line number Diff line number Diff line
@@ -153,7 +153,7 @@ static int pseries_add_processor(struct device_node *np) 
	for (i = 0; i < nthreads; i++)

		cpu_set(i, tmp);



	lock_cpu_hotplug();

	cpu_maps_update_begin();



	BUG_ON(!cpus_subset(cpu_present_map, cpu_possible_map));
@@ -190,7 +190,7 @@ static int pseries_add_processor(struct device_node *np) 
	}

	err = 0;

out_unlock:

	unlock_cpu_hotplug();

	cpu_maps_update_done();

	return err;

}
@@ -211,7 +211,7 @@ static void pseries_remove_processor(struct device_node *np) 


	nthreads = len / sizeof(u32);



	lock_cpu_hotplug();

	cpu_maps_update_begin();

	for (i = 0; i < nthreads; i++) {

		for_each_present_cpu(cpu) {

			if (get_hard_smp_processor_id(cpu) != intserv[i])
@@ -225,7 +225,7 @@ static void pseries_remove_processor(struct device_node *np) 
			printk(KERN_WARNING "Could not find cpu to remove "

			       "with physical id 0x%x\n", intserv[i]);

	}

	unlock_cpu_hotplug();

	cpu_maps_update_done();

}



static int pseries_smp_notifier(struct notifier_block *nb,

arch/powerpc/platforms/pseries/rtasd.c

+4 −4
Original line number Diff line number Diff line
@@ -382,7 +382,7 @@ static void do_event_scan_all_cpus(long delay) 
{

	int cpu;



	lock_cpu_hotplug();

	get_online_cpus();

	cpu = first_cpu(cpu_online_map);

	for (;;) {

		set_cpus_allowed(current, cpumask_of_cpu(cpu));
@@ -390,15 +390,15 @@ static void do_event_scan_all_cpus(long delay) 
		set_cpus_allowed(current, CPU_MASK_ALL);



		/* Drop hotplug lock, and sleep for the specified delay */

		unlock_cpu_hotplug();

		put_online_cpus();

		msleep_interruptible(delay);

		lock_cpu_hotplug();

		get_online_cpus();



		cpu = next_cpu(cpu, cpu_online_map);

		if (cpu == NR_CPUS)

			break;

	}

	unlock_cpu_hotplug();

	put_online_cpus();

}



static int rtasd(void *unused)

arch/x86/kernel/cpu/mtrr/main.c

+4 −4
Original line number Diff line number Diff line
@@ -349,7 +349,7 @@ int mtrr_add_page(unsigned long base, unsigned long size, 
	replace = -1;



	/* No CPU hotplug when we change MTRR entries */

	lock_cpu_hotplug();

	get_online_cpus();

	/*  Search for existing MTRR  */

	mutex_lock(&mtrr_mutex);

	for (i = 0; i < num_var_ranges; ++i) {
@@ -405,7 +405,7 @@ int mtrr_add_page(unsigned long base, unsigned long size, 
	error = i;

 out:

	mutex_unlock(&mtrr_mutex);

	unlock_cpu_hotplug();

	put_online_cpus();

	return error;

}
@@ -495,7 +495,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size) 


	max = num_var_ranges;

	/* No CPU hotplug when we change MTRR entries */

	lock_cpu_hotplug();

	get_online_cpus();

	mutex_lock(&mtrr_mutex);

	if (reg < 0) {

		/*  Search for existing MTRR  */
@@ -536,7 +536,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size) 
	error = reg;

 out:

	mutex_unlock(&mtrr_mutex);

	unlock_cpu_hotplug();

	put_online_cpus();

	return error;

}

/**