[PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Tejun Heo]

The current implementation of set_freezable_with_signal() is buggy and
tricky to get right.  usb-storage is the only user and its use can be
avoided trivially.

All usb-storage wants is to be able to sleep with timeout and get
woken up if freezing() becomes true.  This can be trivially
implemented by doing interruptible wait w/ freezing() included in the
wait condition.  There's no reason to use set_freezable_with_signal().

Perform interruptible wait on freezing() instead of using
set_freezable_with_signal(), which is scheduled for removal.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
---

These two patches are on top of "freezer: fix various bugs and
simplify implementation, take#2" patchset[1] and are also available in
the following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git pm-kill-freezable_with_signal

If usb-storage ppl are okay with it, I think routing this through pm
would be the easiest.  Oh, and this definitely is for the next merge
window.

Thank you.

[1] http://thread.gmane.org/gmane.linux.kernel/1209247

 drivers/usb/storage/usb.c |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
index c325e69..aa84b3d 100644
--- a/drivers/usb/storage/usb.c
+++ b/drivers/usb/storage/usb.c
@@ -831,7 +831,8 @@ static int usb_stor_scan_thread(void * __us)
 
 	dev_dbg(dev, "device found\n");
 
-	set_freezable_with_signal();
+	set_freezable();
+
 	/*
 	 * Wait for the timeout to expire or for a disconnect
 	 *
@@ -839,16 +840,16 @@ static int usb_stor_scan_thread(void * __us)
 	 * fail to freeze, but we can't be non-freezable either. Nor can
 	 * khubd freeze while waiting for scanning to complete as it may
 	 * hold the device lock, causing a hang when suspending devices.
-	 * So we request a fake signal when freezing and use
-	 * interruptible sleep to kick us out of our wait early when
-	 * freezing happens.
+	 * So instead of using wait_event_freezable(), explicitly test
+	 * for (DONT_SCAN || freezing) in interruptible wait and proceed
+	 * if any of DONT_SCAN, freezing or timeout has happened.
 	 */
 	if (delay_use > 0) {
 		dev_dbg(dev, "waiting for device to settle "
 				"before scanning\n");
 		wait_event_interruptible_timeout(us->delay_wait,
-				test_bit(US_FLIDX_DONT_SCAN, &us->dflags),
-				delay_use * HZ);
+				test_bit(US_FLIDX_DONT_SCAN, &us->dflags) ||
+				freezing(current), delay_use * HZ);
 	}
 
 	/* If the device is still connected, perform the scanning */
-- 
1.7.3.1

[PATCH pm 2/2] freezer: kill unused set_freezable_with_signal()

[Tejun Heo]

There's no in-kernel user of set_freezable_with_signal() left.  Mixing
TIF_SIGPENDING with kernel threads can lead to nasty corner cases as
kernel threads never travel signal delivery path on their own.

e.g. the current implementation is buggy in the cancelation path of
__thaw_task().  It calls recalc_sigpending_and_wake() in an attempt to
clear TIF_SIGPENDING but the function never clears it regardless of
sigpending state.  This means that signallable freezable kthreads may
continue executing with !freezing() && stuck TIF_SIGPENDING, which can
be troublesome.

This patch removes set_freezable_with_signal() along with
PF_FREEZER_NOSIG and recalc_sigpending*() calls in freezer.  User
tasks get TIF_SIGPENDING, kernel tasks get woken up and the spurious
sigpending is dealt with in the usual signal delivery path.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/freezer.h |   20 +-------------------
 include/linux/sched.h   |    1 -
 kernel/freezer.c        |   27 ++++++---------------------
 kernel/kthread.c        |    2 +-
 4 files changed, 8 insertions(+), 42 deletions(-)

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index 4b3dc4c..5f32321 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -49,7 +49,7 @@ static inline bool try_to_freeze(void)
 }
 
 extern bool freeze_task(struct task_struct *p);
-extern bool __set_freezable(bool with_signal);
+extern bool set_freezable(void);
 
 #ifdef CONFIG_CGROUP_FREEZER
 extern bool cgroup_freezing(struct task_struct *task);
@@ -105,23 +105,6 @@ static inline int freezer_should_skip(struct task_struct *p)
 }
 
 /*
- * Tell the freezer that the current task should be frozen by it
- */
-static inline bool set_freezable(void)
-{
-	return __set_freezable(false);
-}
-
-/*
- * Tell the freezer that the current task should be frozen by it and that it
- * should send a fake signal to the task to freeze it.
- */
-static inline bool set_freezable_with_signal(void)
-{
-	return __set_freezable(true);
-}
-
-/*
  * Freezer-friendly wrappers around wait_event_interruptible(),
  * wait_event_killable() and wait_event_interruptible_timeout(), originally
  * defined in <linux/wait.h>
@@ -181,7 +164,6 @@ static inline void freezer_do_not_count(void) {}
 static inline void freezer_count(void) {}
 static inline int freezer_should_skip(struct task_struct *p) { return 0; }
 static inline void set_freezable(void) {}
-static inline void set_freezable_with_signal(void) {}
 
 #define wait_event_freezable(wq, condition)				\
 		wait_event_interruptible(wq, condition)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 57f916d..84fd546 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1781,7 +1781,6 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
 #define PF_MEMPOLICY	0x10000000	/* Non-default NUMA mempolicy */
 #define PF_MUTEX_TESTER	0x20000000	/* Thread belongs to the rt mutex tester */
 #define PF_FREEZER_SKIP	0x40000000	/* Freezer should not count it as freezable */
-#define PF_FREEZER_NOSIG 0x80000000	/* Freezer won't send signals to it */
 
 /*
  * Only the _current_ task can read/write to tsk->flags, but other
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 0845321..128c5aa 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -39,7 +39,7 @@ bool freezing_slow_path(struct task_struct *p)
 	if (pm_nosig_freezing || cgroup_freezing(p))
 		return true;
 
-	if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG))
+	if (pm_freezing && !(p->flags & PF_KTHREAD))
 		return true;
 
 	return false;
@@ -72,10 +72,6 @@ bool __refrigerator(bool check_kthr_stop)
 		schedule();
 	}
 
-	spin_lock_irq(&current->sighand->siglock);
-	recalc_sigpending(); /* We sent fake signal, clean it up */
-	spin_unlock_irq(&current->sighand->siglock);
-
 	pr_debug("%s left refrigerator\n", current->comm);
 
 	/*
@@ -120,7 +116,7 @@ bool freeze_task(struct task_struct *p)
 		return false;
 	}
 
-	if (!(p->flags & PF_FREEZER_NOSIG)) {
+	if (!(p->flags & PF_KTHREAD)) {
 		fake_signal_wake_up(p);
 		/*
 		 * fake_signal_wake_up() goes through p's scheduler
@@ -145,28 +141,19 @@ void __thaw_task(struct task_struct *p)
 	 * be visible to @p as waking up implies wmb.  Waking up inside
 	 * freezer_lock also prevents wakeups from leaking outside
 	 * refrigerator.
-	 *
-	 * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
-	 * avoid leaving dangling TIF_SIGPENDING behind.
 	 */
 	spin_lock_irqsave(&freezer_lock, flags);
-	if (frozen(p)) {
+	if (frozen(p))
 		wake_up_process(p);
-	} else {
-		spin_lock(&p->sighand->siglock);
-		recalc_sigpending_and_wake(p);
-		spin_unlock(&p->sighand->siglock);
-	}
 	spin_unlock_irqrestore(&freezer_lock, flags);
 }
 
 /**
- * __set_freezable - make %current freezable
- * @with_signal: do we want %TIF_SIGPENDING for notification too?
+ * set_freezable - make %current freezable
  *
  * Mark %current freezable and enter refrigerator if necessary.
  */
-bool __set_freezable(bool with_signal)
+bool set_freezable(void)
 {
 	might_sleep();
 
@@ -177,10 +164,8 @@ bool __set_freezable(bool with_signal)
 	 */
 	spin_lock_irq(&freezer_lock);
 	current->flags &= ~PF_NOFREEZE;
-	if (with_signal)
-		current->flags &= ~PF_FREEZER_NOSIG;
 	spin_unlock_irq(&freezer_lock);
 
 	return try_to_freeze();
 }
-EXPORT_SYMBOL(__set_freezable);
+EXPORT_SYMBOL(set_freezable);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index a6cbeea..7a4c862 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -282,7 +282,7 @@ int kthreadd(void *unused)
 	set_cpus_allowed_ptr(tsk, cpu_all_mask);
 	set_mems_allowed(node_states[N_HIGH_MEMORY]);
 
-	current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
+	current->flags |= PF_NOFREEZE;
 
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
-- 
1.7.3.1

Re: [PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Seth Forshee]

On Mon, Oct 31, 2011 at 05:37:26PM -0700, Tejun Heo wrote:
> The current implementation of set_freezable_with_signal() is buggy and
> tricky to get right.  usb-storage is the only user and its use can be
> avoided trivially.
> 
> All usb-storage wants is to be able to sleep with timeout and get
> woken up if freezing() becomes true.  This can be trivially
> implemented by doing interruptible wait w/ freezing() included in the
> wait condition.  There's no reason to use set_freezable_with_signal().
> 
> Perform interruptible wait on freezing() instead of using
> set_freezable_with_signal(), which is scheduled for removal.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> Cc: Seth Forshee <seth.forshee@canonical.com>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> ---
> 
> These two patches are on top of "freezer: fix various bugs and
> simplify implementation, take#2" patchset[1] and are also available in
> the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git pm-kill-freezable_with_signal
> 
> If usb-storage ppl are okay with it, I think routing this through pm
> would be the easiest.  Oh, and this definitely is for the next merge
> window.
> 
> Thank you.
> 
> [1] http://thread.gmane.org/gmane.linux.kernel/1209247
> 
>  drivers/usb/storage/usb.c |   13 +++++++------
>  1 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
> index c325e69..aa84b3d 100644
> --- a/drivers/usb/storage/usb.c
> +++ b/drivers/usb/storage/usb.c
> @@ -831,7 +831,8 @@ static int usb_stor_scan_thread(void * __us)
>  
>  	dev_dbg(dev, "device found\n");
>  
> -	set_freezable_with_signal();
> +	set_freezable();
> +
>  	/*
>  	 * Wait for the timeout to expire or for a disconnect
>  	 *
> @@ -839,16 +840,16 @@ static int usb_stor_scan_thread(void * __us)
>  	 * fail to freeze, but we can't be non-freezable either. Nor can
>  	 * khubd freeze while waiting for scanning to complete as it may
>  	 * hold the device lock, causing a hang when suspending devices.
> -	 * So we request a fake signal when freezing and use
> -	 * interruptible sleep to kick us out of our wait early when
> -	 * freezing happens.
> +	 * So instead of using wait_event_freezable(), explicitly test
> +	 * for (DONT_SCAN || freezing) in interruptible wait and proceed
> +	 * if any of DONT_SCAN, freezing or timeout has happened.
>  	 */
>  	if (delay_use > 0) {
>  		dev_dbg(dev, "waiting for device to settle "
>  				"before scanning\n");
>  		wait_event_interruptible_timeout(us->delay_wait,
> -				test_bit(US_FLIDX_DONT_SCAN, &us->dflags),
> -				delay_use * HZ);
> +				test_bit(US_FLIDX_DONT_SCAN, &us->dflags) ||
> +				freezing(current), delay_use * HZ);
>  	}
>  
>  	/* If the device is still connected, perform the scanning */

That looks like it ought to work, and it's definitely less convoluted
than what's there now.  I'd be happy to test it next week when I'm back
home and have access to the machine that prompted the original change.

Seth

Re: [PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Tejun Heo]

On Tue, Nov 01, 2011 at 12:40:10PM -0400, Seth Forshee wrote:
> That looks like it ought to work, and it's definitely less convoluted
> than what's there now.  I'd be happy to test it next week when I'm back
> home and have access to the machine that prompted the original change.

Awesome.  Thanks a lot.

-- 
tejun

Re: [PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Seth Forshee]

On Tue, Nov 01, 2011 at 09:43:51AM -0700, Tejun Heo wrote:
> On Tue, Nov 01, 2011 at 12:40:10PM -0400, Seth Forshee wrote:
> > That looks like it ought to work, and it's definitely less convoluted
> > than what's there now.  I'd be happy to test it next week when I'm back
> > home and have access to the machine that prompted the original change.
> 
> Awesome.  Thanks a lot.

Your changes are working great in my testing.

Acked-by: Seth Forshee <seth.forshee@canonical.com>

Re: [PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Greg KH]

On Mon, Oct 31, 2011 at 05:37:26PM -0700, Tejun Heo wrote:
> The current implementation of set_freezable_with_signal() is buggy and
> tricky to get right.  usb-storage is the only user and its use can be
> avoided trivially.
> 
> All usb-storage wants is to be able to sleep with timeout and get
> woken up if freezing() becomes true.  This can be trivially
> implemented by doing interruptible wait w/ freezing() included in the
> wait condition.  There's no reason to use set_freezable_with_signal().
> 
> Perform interruptible wait on freezing() instead of using
> set_freezable_with_signal(), which is scheduled for removal.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> Cc: Seth Forshee <seth.forshee@canonical.com>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> ---
> 
> These two patches are on top of "freezer: fix various bugs and
> simplify implementation, take#2" patchset[1] and are also available in
> the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git pm-kill-freezable_with_signal
> 
> If usb-storage ppl are okay with it, I think routing this through pm
> would be the easiest.  Oh, and this definitely is for the next merge
> window.

I'm fine with it going that way:
	Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

Re: [PATCH pm 1/2] usb_storage: don't use set_freezable_with_signal()

[Rafael J. Wysocki]

On Tuesday, November 15, 2011, Greg KH wrote:
> On Mon, Oct 31, 2011 at 05:37:26PM -0700, Tejun Heo wrote:
> > The current implementation of set_freezable_with_signal() is buggy and
> > tricky to get right.  usb-storage is the only user and its use can be
> > avoided trivially.
> > 
> > All usb-storage wants is to be able to sleep with timeout and get
> > woken up if freezing() becomes true.  This can be trivially
> > implemented by doing interruptible wait w/ freezing() included in the
> > wait condition.  There's no reason to use set_freezable_with_signal().
> > 
> > Perform interruptible wait on freezing() instead of using
> > set_freezable_with_signal(), which is scheduled for removal.
> > 
> > Signed-off-by: Tejun Heo <tj@kernel.org>
> > Cc: Oleg Nesterov <oleg@redhat.com>
> > Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
> > Cc: Seth Forshee <seth.forshee@canonical.com>
> > Cc: Alan Stern <stern@rowland.harvard.edu>
> > Cc: Greg Kroah-Hartman <gregkh@suse.de>
> > ---
> > 
> > These two patches are on top of "freezer: fix various bugs and
> > simplify implementation, take#2" patchset[1] and are also available in
> > the following git branch.
> > 
> >  git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git pm-kill-freezable_with_signal
> > 
> > If usb-storage ppl are okay with it, I think routing this through pm
> > would be the easiest.  Oh, and this definitely is for the next merge
> > window.
> 
> I'm fine with it going that way:
> 	Acked-by: Greg Kroah-Hartman <gregkh@suse.de>

It's there in my tree already (through the Tejun's pm-freezer branch).

Thanks,
Rafael