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Message-ID: <20121025163959.GB3801@redhat.com>
Date: Thu, 25 Oct 2012 18:39:59 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: rjw@...k.pl, linux-kernel@...r.kernel.org, lizefan@...wei.com,
containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
stable@...r.kernel.org
Subject: [PATCH 1/1] freezer: change ptrace_stop/do_signal_stop to use
freezable_schedule()
Change ptrace_stop() and do_signal_stop() to use freezable_schedule()
rather than rely on subsequent try_to_freeze().
This allows to remove the task_is_stopped_or_traced() checks from
try_to_freeze_tasks() and update_if_frozen(), and this fixes the
unlikely race with ptrace_stop(). If the tracee does not schedule()
it can miss a freezing condition.
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
include/linux/freezer.h | 7 +++----
kernel/cgroup_freezer.c | 3 +--
kernel/freezer.c | 11 ++---------
kernel/power/process.c | 13 +------------
kernel/signal.c | 11 ++---------
5 files changed, 9 insertions(+), 36 deletions(-)
diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index ee89932..8039893 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -134,10 +134,9 @@ static inline bool freezer_should_skip(struct task_struct *p)
}
/*
- * These macros are intended to be used whenever you want allow a task that's
- * sleeping in TASK_UNINTERRUPTIBLE or TASK_KILLABLE state to be frozen. Note
- * that neither return any clear indication of whether a freeze event happened
- * while in this function.
+ * These macros are intended to be used whenever you want allow a sleeping
+ * task to be frozen. Note that neither return any clear indication of
+ * whether a freeze event happened while in this function.
*/
/* Like schedule(), but should not block the freezer. */
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 8a92b0e..bedefd9 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -198,8 +198,7 @@ static void update_if_frozen(struct cgroup *cgroup, struct freezer *freezer)
* completion. Consider it frozen in addition to
* the usual frozen condition.
*/
- if (!frozen(task) && !task_is_stopped_or_traced(task) &&
- !freezer_should_skip(task))
+ if (!frozen(task) && !freezer_should_skip(task))
goto notyet;
}
}
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 11f82a4..c38893b 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -116,17 +116,10 @@ bool freeze_task(struct task_struct *p)
return false;
}
- if (!(p->flags & PF_KTHREAD)) {
+ if (!(p->flags & PF_KTHREAD))
fake_signal_wake_up(p);
- /*
- * fake_signal_wake_up() goes through p's scheduler
- * lock and guarantees that TASK_STOPPED/TRACED ->
- * TASK_RUNNING transition can't race with task state
- * testing in try_to_freeze_tasks().
- */
- } else {
+ else
wake_up_state(p, TASK_INTERRUPTIBLE);
- }
spin_unlock_irqrestore(&freezer_lock, flags);
return true;
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 87da817..d5a258b 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -48,18 +48,7 @@ static int try_to_freeze_tasks(bool user_only)
if (p == current || !freeze_task(p))
continue;
- /*
- * Now that we've done set_freeze_flag, don't
- * perturb a task in TASK_STOPPED or TASK_TRACED.
- * It is "frozen enough". If the task does wake
- * up, it will immediately call try_to_freeze.
- *
- * Because freeze_task() goes through p's scheduler lock, it's
- * guaranteed that TASK_STOPPED/TRACED -> TASK_RUNNING
- * transition can't race with task state testing here.
- */
- if (!task_is_stopped_or_traced(p) &&
- !freezer_should_skip(p))
+ if (!freezer_should_skip(p))
todo++;
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
diff --git a/kernel/signal.c b/kernel/signal.c
index 0af8868..1660d7d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1908,7 +1908,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
preempt_disable();
read_unlock(&tasklist_lock);
preempt_enable_no_resched();
- schedule();
+ freezable_schedule();
} else {
/*
* By the time we got the lock, our tracer went away.
@@ -1930,13 +1930,6 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
}
/*
- * While in TASK_TRACED, we were considered "frozen enough".
- * Now that we woke up, it's crucial if we're supposed to be
- * frozen that we freeze now before running anything substantial.
- */
- try_to_freeze();
-
- /*
* We are back. Now reacquire the siglock before touching
* last_siginfo, so that we are sure to have synchronized with
* any signal-sending on another CPU that wants to examine it.
@@ -2092,7 +2085,7 @@ static bool do_signal_stop(int signr)
}
/* Now we don't run again until woken by SIGCONT or SIGKILL */
- schedule();
+ freezable_schedule();
return true;
} else {
/*
--
1.5.5.1
--
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