On Saturday, 3 March 2007 18:32, Oleg Nesterov wrote:
> On 03/02, Paul E. McKenney wrote:
> >
> > On Sat, Mar 03, 2007 at 02:33:37AM +0300, Oleg Nesterov wrote:
> > > On 03/02, Paul E. McKenney wrote:
> > > >
> > > > One way to embed try_to_freeze() into kthread_should_stop() might be
> > > > as follows:
> > > >
> > > > int kthread_should_stop(void)
> > > > {
> > > > if (kthread_stop_info.k == current)
> > > > return 1;
> > > > try_to_freeze();
> > > > return 0;
> > > > }
> > >
> > > I think this is dangerous. For example, worker_thread() will probably
> > > need some special actions after return from refrigerator. Also, a kernel
> > > thread may check kthread_should_stop() in the place where try_to_freeze()
> > > is not safe.
> > >
> > > Perhaps we should introduce a new helper which does this.
> >
> > Good point -- the return value from try_to_freeze() is lost if one uses
> > the above approach. About one third of the calls to try_to_freeze()
> > in 2.6.20 pay attention to the return value.
> >
> > One approach would be to have a kthread_should_stop_nofreeze() for those
> > cases, and let the default be to try to freeze.
>
> I personally think we should do the opposite, add
> kthread_should_stop_check_freeze()
> or something. kthread_should_stop() is like signal_pending(), we can use
> it under spin_lock (and it is probably used this way by some out-of-tree
> driver). The new helper is obviously "might_sleep()".
Something like this, perhaps:
include/linux/kthread.h | 1 +
kernel/kthread.c | 16 ++++++++++++++++
kernel/rcutorture.c | 5 ++---
3 files changed, 19 insertions(+), 3 deletions(-)
Index: linux-2.6.21-rc3-mm2/kernel/kthread.c
===================================================================
--- linux-2.6.21-rc3-mm2.orig/kernel/kthread.c 2007-03-08 21:58:48.000000000
+0100
+++ linux-2.6.21-rc3-mm2/kernel/kthread.c 2007-03-11 18:32:59.000000000
+0100
@@ -13,6 +13,7 @@
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mutex.h>
+#include <linux/freezer.h>
#include <asm/semaphore.h>
/*
@@ -60,6 +61,21 @@ int kthread_should_stop(void)
}
EXPORT_SYMBOL(kthread_should_stop);
+/**
+ * kthread_should_stop_check_freeze - check if the thread should return now and
+ * if not, check if there is a freezing request pending for it.
+ */
+int kthread_should_stop_check_freeze(void)
+{
+ might_sleep();
+ if (kthread_stop_info.k == current)
+ return 1;
+
+ try_to_freeze();
+ return 0;
+}
+EXPORT_SYMBOL(kthread_should_stop_check_freeze);
+
static void kthread_exit_files(void)
{
struct fs_struct *fs;
Index: linux-2.6.21-rc3-mm2/include/linux/kthread.h
===================================================================
--- linux-2.6.21-rc3-mm2.orig/include/linux/kthread.h 2007-02-04
19:44:54.000000000 +0100
+++ linux-2.6.21-rc3-mm2/include/linux/kthread.h 2007-03-11
18:37:10.000000000 +0100
@@ -29,5 +29,6 @@ struct task_struct *kthread_create(int (
void kthread_bind(struct task_struct *k, unsigned int cpu);
int kthread_stop(struct task_struct *k);
int kthread_should_stop(void);
+int kthread_should_stop_check_freeze(void);
#endif /* _LINUX_KTHREAD_H */
Index: linux-2.6.21-rc3-mm2/kernel/rcutorture.c
===================================================================
--- linux-2.6.21-rc3-mm2.orig/kernel/rcutorture.c 2007-03-11
11:39:06.000000000 +0100
+++ linux-2.6.21-rc3-mm2/kernel/rcutorture.c 2007-03-11 18:45:00.000000000
+0100
@@ -540,10 +540,9 @@ rcu_torture_writer(void *arg)
}
rcu_torture_current_version++;
oldbatch = cur_ops->completed();
- try_to_freeze();
- } while (!kthread_should_stop() && !fullstop);
+ } while (!kthread_should_stop_check_freeze() && !fullstop);
VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
- while (!kthread_should_stop())
+ while (!kthread_should_stop_check_freeze())
schedule_timeout_uninterruptible(1);
return 0;
}
-
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