linux/kernel/power/process.c
Waiman Long 2125c0034c cgroup/cpuset: Make cpuset hotplug processing synchronous
Since commit 3a5a6d0c2b03("cpuset: don't nest cgroup_mutex inside
get_online_cpus()"), cpuset hotplug was done asynchronously via a work
function. This is to avoid recursive locking of cgroup_mutex.

Since then, the cgroup locking scheme has changed quite a bit. A
cpuset_mutex was introduced to protect cpuset specific operations.
The cpuset_mutex is then replaced by a cpuset_rwsem. With commit
d74b27d63a ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock
order"), cpu_hotplug_lock is acquired before cpuset_rwsem. Later on,
cpuset_rwsem is reverted back to cpuset_mutex. All these locking changes
allow the hotplug code to call into cpuset core directly.

The following commits were also merged due to the asynchronous nature
of cpuset hotplug processing.

  - commit b22afcdf04 ("cpu/hotplug: Cure the cpusets trainwreck")
  - commit 50e7663233 ("sched/cpuset/pm: Fix cpuset vs. suspend-resume
    bugs")
  - commit 28b89b9e6f ("cpuset: handle race between CPU hotplug and
    cpuset_hotplug_work")

Clean up all these bandages by making cpuset hotplug
processing synchronous again with the exception that the call to
cgroup_transfer_tasks() to transfer tasks out of an empty cgroup v1
cpuset, if necessary, will still be done via a work function due to the
existing cgroup_mutex -> cpu_hotplug_lock dependency. It is possible
to reverse that dependency, but that will require updating a number of
different cgroup controllers. This special hotplug code path should be
rarely taken anyway.

As all the cpuset states will be updated by the end of the hotplug
operation, we can revert most the above commits except commit
50e7663233 ("sched/cpuset/pm: Fix cpuset vs. suspend-resume bugs")
which is partially reverted.  Also removing some cpus_read_lock trylock
attempts in the cpuset partition code as they are no longer necessary
since the cpu_hotplug_lock is now held for the whole duration of the
cpuset hotplug code path.

Signed-off-by: Waiman Long <longman@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2024-04-08 07:39:16 -10:00

234 lines
5.4 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* drivers/power/process.c - Functions for starting/stopping processes on
* suspend transitions.
*
* Originally from swsusp.
*/
#include <linux/interrupt.h>
#include <linux/oom.h>
#include <linux/suspend.h>
#include <linux/module.h>
#include <linux/sched/debug.h>
#include <linux/sched/task.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
#include <linux/delay.h>
#include <linux/workqueue.h>
#include <linux/kmod.h>
#include <trace/events/power.h>
#include <linux/cpuset.h>
/*
* Timeout for stopping processes
*/
unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
static int try_to_freeze_tasks(bool user_only)
{
const char *what = user_only ? "user space processes" :
"remaining freezable tasks";
struct task_struct *g, *p;
unsigned long end_time;
unsigned int todo;
bool wq_busy = false;
ktime_t start, end, elapsed;
unsigned int elapsed_msecs;
bool wakeup = false;
int sleep_usecs = USEC_PER_MSEC;
pr_info("Freezing %s\n", what);
start = ktime_get_boottime();
end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
if (!user_only)
freeze_workqueues_begin();
while (true) {
todo = 0;
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
if (p == current || !freeze_task(p))
continue;
todo++;
}
read_unlock(&tasklist_lock);
if (!user_only) {
wq_busy = freeze_workqueues_busy();
todo += wq_busy;
}
if (!todo || time_after(jiffies, end_time))
break;
if (pm_wakeup_pending()) {
wakeup = true;
break;
}
/*
* We need to retry, but first give the freezing tasks some
* time to enter the refrigerator. Start with an initial
* 1 ms sleep followed by exponential backoff until 8 ms.
*/
usleep_range(sleep_usecs / 2, sleep_usecs);
if (sleep_usecs < 8 * USEC_PER_MSEC)
sleep_usecs *= 2;
}
end = ktime_get_boottime();
elapsed = ktime_sub(end, start);
elapsed_msecs = ktime_to_ms(elapsed);
if (todo) {
pr_err("Freezing %s %s after %d.%03d seconds "
"(%d tasks refusing to freeze, wq_busy=%d):\n", what,
wakeup ? "aborted" : "failed",
elapsed_msecs / 1000, elapsed_msecs % 1000,
todo - wq_busy, wq_busy);
if (wq_busy)
show_freezable_workqueues();
if (!wakeup || pm_debug_messages_on) {
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
if (p != current && freezing(p) && !frozen(p))
sched_show_task(p);
}
read_unlock(&tasklist_lock);
}
} else {
pr_info("Freezing %s completed (elapsed %d.%03d seconds)\n",
what, elapsed_msecs / 1000, elapsed_msecs % 1000);
}
return todo ? -EBUSY : 0;
}
/**
* freeze_processes - Signal user space processes to enter the refrigerator.
* The current thread will not be frozen. The same process that calls
* freeze_processes must later call thaw_processes.
*
* On success, returns 0. On failure, -errno and system is fully thawed.
*/
int freeze_processes(void)
{
int error;
error = __usermodehelper_disable(UMH_FREEZING);
if (error)
return error;
/* Make sure this task doesn't get frozen */
current->flags |= PF_SUSPEND_TASK;
if (!pm_freezing)
static_branch_inc(&freezer_active);
pm_wakeup_clear(0);
pm_freezing = true;
error = try_to_freeze_tasks(true);
if (!error)
__usermodehelper_set_disable_depth(UMH_DISABLED);
BUG_ON(in_atomic());
/*
* Now that the whole userspace is frozen we need to disable
* the OOM killer to disallow any further interference with
* killable tasks. There is no guarantee oom victims will
* ever reach a point they go away we have to wait with a timeout.
*/
if (!error && !oom_killer_disable(msecs_to_jiffies(freeze_timeout_msecs)))
error = -EBUSY;
if (error)
thaw_processes();
return error;
}
/**
* freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
*
* On success, returns 0. On failure, -errno and only the kernel threads are
* thawed, so as to give a chance to the caller to do additional cleanups
* (if any) before thawing the userspace tasks. So, it is the responsibility
* of the caller to thaw the userspace tasks, when the time is right.
*/
int freeze_kernel_threads(void)
{
int error;
pm_nosig_freezing = true;
error = try_to_freeze_tasks(false);
BUG_ON(in_atomic());
if (error)
thaw_kernel_threads();
return error;
}
void thaw_processes(void)
{
struct task_struct *g, *p;
struct task_struct *curr = current;
trace_suspend_resume(TPS("thaw_processes"), 0, true);
if (pm_freezing)
static_branch_dec(&freezer_active);
pm_freezing = false;
pm_nosig_freezing = false;
oom_killer_enable();
pr_info("Restarting tasks ... ");
__usermodehelper_set_disable_depth(UMH_FREEZING);
thaw_workqueues();
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
/* No other threads should have PF_SUSPEND_TASK set */
WARN_ON((p != curr) && (p->flags & PF_SUSPEND_TASK));
__thaw_task(p);
}
read_unlock(&tasklist_lock);
WARN_ON(!(curr->flags & PF_SUSPEND_TASK));
curr->flags &= ~PF_SUSPEND_TASK;
usermodehelper_enable();
schedule();
pr_cont("done.\n");
trace_suspend_resume(TPS("thaw_processes"), 0, false);
}
void thaw_kernel_threads(void)
{
struct task_struct *g, *p;
pm_nosig_freezing = false;
pr_info("Restarting kernel threads ... ");
thaw_workqueues();
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
if (p->flags & PF_KTHREAD)
__thaw_task(p);
}
read_unlock(&tasklist_lock);
schedule();
pr_cont("done.\n");
}