linux/kernel/power/process.c
Michal Hocko 7d2e7a22cf oom, suspend: fix oom_killer_disable vs. pm suspend properly
Commit 7407054209 ("oom, suspend: fix oom_reaper vs.
oom_killer_disable race") has workaround an existing race between
oom_killer_disable and oom_reaper by adding another round of
try_to_freeze_tasks after the oom killer was disabled.  This was the
easiest thing to do for a late 4.7 fix.  Let's fix it properly now.

After "oom: keep mm of the killed task available" we no longer have to
call exit_oom_victim from the oom reaper because we have stable mm
available and hide the oom_reaped mm by MMF_OOM_SKIP flag.  So let's
remove exit_oom_victim and the race described in the above commit
doesn't exist anymore if.

Unfortunately this alone is not sufficient for the oom_killer_disable
usecase because now we do not have any reliable way to reach
exit_oom_victim (the victim might get stuck on a way to exit for an
unbounded amount of time).  OOM killer can cope with that by checking mm
flags and move on to another victim but we cannot do the same for
oom_killer_disable as we would lose the guarantee of no further
interference of the victim with the rest of the system.  What we can do
instead is to cap the maximum time the oom_killer_disable waits for
victims.  The only current user of this function (pm suspend) already
has a concept of timeout for back off so we can reuse the same value
there.

Let's drop set_freezable for the oom_reaper kthread because it is no
longer needed as the reaper doesn't wake or thaw any processes.

Link: http://lkml.kernel.org/r/1472119394-11342-7-git-send-email-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-10-07 18:46:27 -07:00

240 lines
5.4 KiB
C

/*
* drivers/power/process.c - Functions for starting/stopping processes on
* suspend transitions.
*
* Originally from swsusp.
*/
#undef DEBUG
#include <linux/interrupt.h>
#include <linux/oom.h>
#include <linux/suspend.h>
#include <linux/module.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>
/*
* Timeout for stopping processes
*/
unsigned int __read_mostly freeze_timeout_msecs = 20 * MSEC_PER_SEC;
static int try_to_freeze_tasks(bool user_only)
{
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;
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;
if (!freezer_should_skip(p))
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_cont("\n");
pr_err("Freezing of tasks %s after %d.%03d seconds "
"(%d tasks refusing to freeze, wq_busy=%d):\n",
wakeup ? "aborted" : "failed",
elapsed_msecs / 1000, elapsed_msecs % 1000,
todo - wq_busy, wq_busy);
if (wq_busy)
show_workqueue_state();
if (!wakeup) {
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
if (p != current && !freezer_should_skip(p)
&& freezing(p) && !frozen(p))
sched_show_task(p);
}
read_unlock(&tasklist_lock);
}
} else {
pr_cont("(elapsed %d.%03d seconds) ", 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)
atomic_inc(&system_freezing_cnt);
pm_wakeup_clear();
pr_info("Freezing user space processes ... ");
pm_freezing = true;
error = try_to_freeze_tasks(true);
if (!error) {
__usermodehelper_set_disable_depth(UMH_DISABLED);
pr_cont("done.");
}
pr_cont("\n");
BUG_ON(in_atomic());
/*
* Now that the whole userspace is frozen we need to disbale
* 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;
pr_info("Freezing remaining freezable tasks ... ");
pm_nosig_freezing = true;
error = try_to_freeze_tasks(false);
if (!error)
pr_cont("done.");
pr_cont("\n");
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)
atomic_dec(&system_freezing_cnt);
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 | PF_WQ_WORKER))
__thaw_task(p);
}
read_unlock(&tasklist_lock);
schedule();
pr_cont("done.\n");
}