linux-kernel - PATCH: freezer: add fake signal clearing back when thaw task

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Date:	Thu, 21 Feb 2013 14:19:21 +0800
From:	Lianwei Wang <lianwei.wang@...il.com>
To:	linux-kernel@...r.kernel.org, tj@...nel.org
Subject: PATCH: freezer: add fake signal clearing back when thaw task

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@...il.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@...il.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

Download attachment "0001-freezer-add-fake-signal-clearing-back-when-thaw-task.patch" of type "application/octet-stream" (1805 bytes)