[PATCH] Hibernation: Fix lockdep report (v2)

[PATCH] Hibernation: Fix lockdep report (v2)

[Rafael J. Wysocki]

[Len, please add this patch to the suspend branch, thanks.]
---
From: Johannes Berg <johannes@sipsolutions.net>

Lockdep reports a circular locking dependency in the hibernate code
because
 - during system boot hibernate code (from an initcall) locks pm_mutex
   and then a sysfs buffer mutex via name_to_dev_t
 - during regular operation hibernate code locks pm_mutex under a
   sysfs buffer mutex because it's called from sysfs methods.

The deadlock can never happen because during initcall invocation nothing
can write to sysfs yet. This removes the lockdep report by marking the
initcall locking as being in a different class.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 kernel/power/disk.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/power/disk.c
===================================================================
--- linux-2.6.orig/kernel/power/disk.c
+++ linux-2.6/kernel/power/disk.c
@@ -456,7 +456,17 @@ static int software_resume(void)
 	int error;
 	unsigned int flags;
 
-	mutex_lock(&pm_mutex);
+	/*
+	 * name_to_dev_t() below takes a sysfs buffer mutex when sysfs
+	 * is configured into the kernel. Since the regular hibernate
+	 * trigger path is via sysfs which takes a buffer mutex before
+	 * calling hibernate functions (which take pm_mutex) this can
+	 * cause lockdep to complain about a possible ABBA deadlock
+	 * which cannot happen since we're in the boot code here and
+	 * sysfs can't be invoked yet. Therefore, we use a subclass
+	 * here to avoid lockdep complaining.
+	 */
+	mutex_lock_nested(&pm_mutex, SINGLE_DEPTH_NESTING);
 	if (!swsusp_resume_device) {
 		if (!strlen(resume_file)) {
 			mutex_unlock(&pm_mutex);

Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Pavel Machek]

On Sun 2007-11-04 14:59:22, Rafael J. Wysocki wrote:
> [Len, please add this patch to the suspend branch, thanks.]
> ---
> From: Johannes Berg <johannes@sipsolutions.net>
> 
> Lockdep reports a circular locking dependency in the hibernate code
> because
>  - during system boot hibernate code (from an initcall) locks pm_mutex
>    and then a sysfs buffer mutex via name_to_dev_t
>  - during regular operation hibernate code locks pm_mutex under a
>    sysfs buffer mutex because it's called from sysfs methods.
> 
> The deadlock can never happen because during initcall invocation nothing
> can write to sysfs yet. This removes the lockdep report by marking the
> initcall locking as being in a different class.
> 
> Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Pavel Machek <pavel@ucw.cz>
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

ACK.
								Pavel

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Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Johannes Berg]

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On Sun, 2007-11-04 at 14:59 +0100, Rafael J. Wysocki wrote:
> [Len, please add this patch to the suspend branch, thanks.]
> ---
> From: Johannes Berg <johannes@sipsolutions.net>
> 
> Lockdep reports a circular locking dependency in the hibernate code
> because
>  - during system boot hibernate code (from an initcall) locks pm_mutex
>    and then a sysfs buffer mutex via name_to_dev_t
>  - during regular operation hibernate code locks pm_mutex under a
>    sysfs buffer mutex because it's called from sysfs methods.

Ping? Do I need to follow this or will somebody take care to merge it
before .24 closes?

Thanks,
Johannes

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Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Peter Zijlstra]

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On Tue, 2007-11-13 at 19:45 +0100, Johannes Berg wrote:
> On Sun, 2007-11-04 at 14:59 +0100, Rafael J. Wysocki wrote:
> > [Len, please add this patch to the suspend branch, thanks.]
> > ---
> > From: Johannes Berg <johannes@sipsolutions.net>
> > 
> > Lockdep reports a circular locking dependency in the hibernate code
> > because
> >  - during system boot hibernate code (from an initcall) locks pm_mutex
> >    and then a sysfs buffer mutex via name_to_dev_t
> >  - during regular operation hibernate code locks pm_mutex under a
> >    sysfs buffer mutex because it's called from sysfs methods.
> 
> Ping? Do I need to follow this or will somebody take care to merge it
> before .24 closes?

I can feed it to Linus through the lockdep tree if Len hasn't picked it
up yet, Len?

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Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Rafael J. Wysocki]

On Tuesday, 13 of November 2007, Johannes Berg wrote:
> 
> On Sun, 2007-11-04 at 14:59 +0100, Rafael J. Wysocki wrote:
> > [Len, please add this patch to the suspend branch, thanks.]
> > ---
> > From: Johannes Berg <johannes@sipsolutions.net>
> > 
> > Lockdep reports a circular locking dependency in the hibernate code
> > because
> >  - during system boot hibernate code (from an initcall) locks pm_mutex
> >    and then a sysfs buffer mutex via name_to_dev_t
> >  - during regular operation hibernate code locks pm_mutex under a
> >    sysfs buffer mutex because it's called from sysfs methods.
> 
> Ping? Do I need to follow this or will somebody take care to merge it
> before .24 closes?

I wanted it to go via Len's tree, but unfortunately Len has not been responsive
recently.

I'll push it to Andrew later today.

Thanks,
Rafael

[PATCH] Hibernation: Fix lockdep report (v2)

[Rafael J. Wysocki]

[Andrew, please consider this as 2.6.24 material, thanks.]
---
From: Johannes Berg <johannes@sipsolutions.net>

Lockdep reports a circular locking dependency in the hibernate code
because
 - during system boot hibernate code (from an initcall) locks pm_mutex
   and then a sysfs buffer mutex via name_to_dev_t
 - during regular operation hibernate code locks pm_mutex under a
   sysfs buffer mutex because it's called from sysfs methods.

The deadlock can never happen because during initcall invocation nothing
can write to sysfs yet. This removes the lockdep report by marking the
initcall locking as being in a different class.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 kernel/power/disk.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/power/disk.c
===================================================================
--- linux-2.6.orig/kernel/power/disk.c
+++ linux-2.6/kernel/power/disk.c
@@ -456,7 +456,17 @@ static int software_resume(void)
 	int error;
 	unsigned int flags;
 
-	mutex_lock(&pm_mutex);
+	/*
+	 * name_to_dev_t() below takes a sysfs buffer mutex when sysfs
+	 * is configured into the kernel. Since the regular hibernate
+	 * trigger path is via sysfs which takes a buffer mutex before
+	 * calling hibernate functions (which take pm_mutex) this can
+	 * cause lockdep to complain about a possible ABBA deadlock
+	 * which cannot happen since we're in the boot code here and
+	 * sysfs can't be invoked yet. Therefore, we use a subclass
+	 * here to avoid lockdep complaining.
+	 */
+	mutex_lock_nested(&pm_mutex, SINGLE_DEPTH_NESTING);
 	if (!swsusp_resume_device) {
 		if (!strlen(resume_file)) {
 			mutex_unlock(&pm_mutex);

Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Peter Zijlstra]

On Wed, 2007-11-14 at 22:42 +0000, Pavel Machek wrote:
> On Wed 2007-11-14 22:25:57, Rafael J. Wysocki wrote:
> > [Andrew, please consider this as 2.6.24 material, thanks.]
> > ---
> > From: Johannes Berg <johannes@sipsolutions.net>
> > 
> > Lockdep reports a circular locking dependency in the hibernate code
> > because
> >  - during system boot hibernate code (from an initcall) locks pm_mutex
> >    and then a sysfs buffer mutex via name_to_dev_t
> >  - during regular operation hibernate code locks pm_mutex under a
> >    sysfs buffer mutex because it's called from sysfs methods.
> > 
> > The deadlock can never happen because during initcall invocation nothing
> > can write to sysfs yet. This removes the lockdep report by marking the
> > initcall locking as being in a different class.
> > 
> > Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
> > Cc: Alan Stern <stern@rowland.harvard.edu>
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>

I guess mine got lost too :-)

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> > Cc: Pavel Machek <pavel@ucw.cz>
> 
> ACK...
> 

Re: [PATCH] Hibernation: Fix lockdep report (v2)

[Pavel Machek]

On Wed 2007-11-14 22:25:57, Rafael J. Wysocki wrote:
> [Andrew, please consider this as 2.6.24 material, thanks.]
> ---
> From: Johannes Berg <johannes@sipsolutions.net>
> 
> Lockdep reports a circular locking dependency in the hibernate code
> because
>  - during system boot hibernate code (from an initcall) locks pm_mutex
>    and then a sysfs buffer mutex via name_to_dev_t
>  - during regular operation hibernate code locks pm_mutex under a
>    sysfs buffer mutex because it's called from sysfs methods.
> 
> The deadlock can never happen because during initcall invocation nothing
> can write to sysfs yet. This removes the lockdep report by marking the
> initcall locking as being in a different class.
> 
> Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Pavel Machek <pavel@ucw.cz>

ACK...

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html