PATCH: freezer: add fake signal clearing back when thaw task

Lianwei Wang
2013-02-21T06:19:42Z

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Hi Tejun Heo and all,

The commit of "34b087e freezer: kill unused
set_freezable_with_signal()" remove recalc_sigpending*() calls in
freezer, so the user tasks get TIF_SIGPENDING fake signal that is set
when freezing userspace process. It left the fake signal to userspcae
which cause the userspace task that wait_event_freezable and friends
return a wrong ERESTARTSYS. This is not good because it waste cpu time
to handle the fake signal.

Can we just call the recalc_sigpending to clear the fake signal for
userspace tasks? as below patch do:

>From 176fccee178bc0185d92853dd2f521c9166b0853 Mon Sep 17 00:00:00 2001
From: Lianwei Wang <lianwei.wang@gmail.com>
Date: Mon, 21 Jan 2013 18:21:26 +0800
Subject: [PATCH] freezer: add fake signal clearing back when thaw task

The fake TIF_SIGPENDING is set during freeze userspace process, but it
is not cleared when thaw tasks after below commit:
34b087e freezer: kill unused set_freezable_with_signal()

This will cause the userspace task that wait_event_freezable and friends
return a wrong ERESTARTSYS. This is not good because it waste cpu time to
handle the fake signal.

Try to clear the TIF_SIGPENDING flag for userspace apps when wakeup the
frozen task to fix this issue.

Change-Id: I91c90ad2ee9a46c42e3b39a7384ec81e97bc0394
Signed-off-by: Lianwei Wang <lianwei.wang@gmail.com>
---
kernel/freezer.c | 14 ++++++++++++++
1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index c38893b..09557f6 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -46,6 +46,16 @@ bool freezing_slow_path(struct task_struct *p)
}
EXPORT_SYMBOL(freezing_slow_path);

+static void fake_signal_clear(struct task_struct *p)
+{
+ unsigned long flags;
+
+ if (lock_task_sighand(p, &flags)) {
+ recalc_sigpending();
+ unlock_task_sighand(p, &flags);
+ }
+}
+
/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
@@ -74,6 +84,10 @@ bool __refrigerator(bool check_kthr_stop)

pr_debug("%s left refrigerator\n", current->comm);

+ if (!(current->flags & PF_KTHREAD))
+ if (test_tsk_thread_flag(current, TIF_SIGPENDING))
+ fake_signal_clear(current);
+
/*
* Restore saved task state before returning. The mb'd version
* needs to be used; otherwise, it might silently break
--
1.7.4.1

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From 176fccee178bc0185d92853dd2f521c9166b0853 Mon Sep 17 00:00:00 2001
From: Lianwei Wang <lianwei.wang@gmail.com>
Date: Mon, 21 Jan 2013 18:21:26 +0800
Subject: [PATCH] freezer: add fake signal clearing back when thaw task

The fake TIF_SIGPENDING is set during freeze userspace process, but it
is not cleared when thaw tasks after below commit:
34b087e freezer: kill unused set_freezable_with_signal()

This will cause the userspace task that wait_event_freezable and friends
return a wrong ERESTARTSYS. This is not good because it waste cpu time to
handle the fake signal.

Try to clear the TIF_SIGPENDING flag for userspace apps when wakeup the
frozen task to fix this issue.

Change-Id: I91c90ad2ee9a46c42e3b39a7384ec81e97bc0394
Signed-off-by: Lianwei Wang <lianwei.wang@gmail.com>
---
kernel/freezer.c | 14 ++++++++++++++
1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index c38893b..09557f6 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -46,6 +46,16 @@ bool freezing_slow_path(struct task_struct *p)
}
EXPORT_SYMBOL(freezing_slow_path);

+static void fake_signal_clear(struct task_struct *p)
+{
+ unsigned long flags;
+
+ if (lock_task_sighand(p, &flags)) {
+ recalc_sigpending();
+ unlock_task_sighand(p, &flags);
+ }
+}
+
/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
@@ -74,6 +84,10 @@ bool __refrigerator(bool check_kthr_stop)

pr_debug("%s left refrigerator\n", current->comm);

+ if (!(current->flags & PF_KTHREAD))
+ if (test_tsk_thread_flag(current, TIF_SIGPENDING))
+ fake_signal_clear(current);
+
/*
* Restore saved task state before returning. The mb'd version
* needs to be used; otherwise, it might silently break
--
1.7.4.1