Message-ID: <20100112144414.GA3925@hack>
Date:	Tue, 12 Jan 2010 22:44:14 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Arjan van de Ven <arjan@...radead.org>,
	Tejun Heo <tj@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: 2.6.33-rc3 -- INFO: possible recursive locking --
	(s_active){++++.+}, at: [<c10d2941>] sysfs_hash_and_remove+0x3d/0x4f

On Sun, Jan 10, 2010 at 06:26:29PM -0800, Eric W. Biederman wrote:
>"Rafael J. Wysocki" <rjw@...k.pl> writes:
>
>> On Sunday 10 January 2010, Eric W. Biederman wrote:
>>> Américo Wang <xiyou.wangcong@...il.com> writes:
>>> 
>>> > On Sun, Jan 10, 2010 at 4:47 PM, Américo Wang <xiyou.wangcong@...il.com> wrote:
>>> >>
>>> >> On Wed, Jan 06, 2010 at 07:54:59AM -0500, Miles Lane wrote:
>>> >> >[ 6967.926563] ACPI: Preparing to enter system sleep state S3
>>> >> >[ 6967.956156] Disabling non-boot CPUs ...
>>> >> >[ 6967.970401]
>>> >> >[ 6967.970408] =============================================
>>> >> >[ 6967.970419] [ INFO: possible recursive locking detected ]
>>> >> >[ 6967.970431] 2.6.33-rc2-git6 #27
>>> >> >[ 6967.970439] ---------------------------------------------
>>> >> >[ 6967.970450] pm-suspend/22147 is trying to acquire lock:
>>> >> >[ 6967.970460]  (s_active){++++.+}, at: [<c10d2941>]
>>> >> >sysfs_hash_and_remove+0x3d/0x4f
>>> >> >[ 6967.970493]
>>> >> >[ 6967.970497] but task is already holding lock:
>>> >> >[ 6967.970506]  (s_active){++++.+}, at: [<c10d4110>]
>>> >> >sysfs_get_active_two+0x16/0x36
>>> >> >[ 6967.970531]
>>> >> >[ 6967.970535] other info that might help us debug this:
>>> >> >[ 6967.970547] 6 locks held by pm-suspend/22147:
>>> >> >[ 6967.970556]  #0:  (&buffer->mutex){+.+.+.}, at: [<c10d2ff3>]
>>> >> >sysfs_write_file+0x25/0xeb
>>> >> >[ 6967.970584]  #1:  (s_active){++++.+}, at: [<c10d4110>]
>>> >> >sysfs_get_active_two+0x16/0x36
>>> >> >[ 6967.970612]  #2:  (s_active){++++.+}, at: [<c10d411b>]
>>> >> >sysfs_get_active_two+0x21/0x36
>>> >> >[ 6967.970639]  #3:  (pm_mutex){+.+.+.}, at: [<c1056f00>] enter_state+0x26/0x114
>>> >> >[ 6967.970668]  #4:  (cpu_add_remove_lock){+.+.+.}, at: [<c102ea10>]
>>> >> >cpu_maps_update_begin+0xf/0x11
>>> >> >[ 6967.970697]  #5:  (cpu_hotplug.lock){+.+.+.}, at: [<c102ea3e>]
>>> >> >cpu_hotplug_begin+0x1d/0x40
>>> >> >[ 6967.970724]
>>> >> >[ 6967.970728] stack backtrace:
>>> >> >[ 6967.970740] Pid: 22147, comm: pm-suspend Not tainted 2.6.33-rc2-git6 #27
>>> >> >[ 6967.970751] Call Trace:
>>> >> >[ 6967.970771]  [<c12cc9bf>] ? printk+0xf/0x18
>>> >> >[ 6967.970791]  [<c104dcdb>] __lock_acquire+0x817/0xb6d
>>> >> >[ 6967.970812]  [<c104cbb2>] ? mark_held_locks+0x43/0x5b
>>> >> >[ 6967.970831]  [<c104cf4c>] ? debug_check_no_locks_freed+0xfd/0x107
>>> >> >[ 6967.970851]  [<c104ce1a>] ? trace_hardirqs_on_caller+0x108/0x130
>>> >> >[ 6967.970871]  [<c104e08d>] lock_acquire+0x5c/0x73
>>> >> >[ 6967.970890]  [<c10d2941>] ? sysfs_hash_and_remove+0x3d/0x4f
>>> >> >[ 6967.970910]  [<c10d3ee6>] sysfs_addrm_finish+0x9a/0xfe
>>> >> >[ 6967.970929]  [<c10d2941>] ? sysfs_hash_and_remove+0x3d/0x4f
>>> >> >[ 6967.970953]  [<c10d2941>] sysfs_hash_and_remove+0x3d/0x4f
>>> >> >[ 6967.970974]  [<c10d4c11>] sysfs_remove_group+0x52/0x81
>>> >> >[ 6967.970993]  [<c12cab5d>] mc_cpu_callback+0x73/0x9a
>>> >> >[ 6967.971014]  [<c10427d0>] notifier_call_chain+0x51/0x78
>>> >> >[ 6967.971034]  [<c104285c>] __raw_notifier_call_chain+0xe/0x10
>>> >> >[ 6967.971054]  [<c12c094b>] _cpu_down+0x7a/0x235
>>> >> >[ 6967.971074]  [<c102eab9>] disable_nonboot_cpus+0x58/0xe0
>>> >> >[ 6967.971093]  [<c1056e20>] suspend_devices_and_enter+0xb9/0x173
>>> >> >[ 6967.971094]  [<c1056fa2>] enter_state+0xc8/0x114
>>> >> >[ 6967.971094]  [<c1056855>] state_store+0x93/0xa7
>>> >> >[ 6967.971094]  [<c10567c2>] ? state_store+0x0/0xa7
>>> >> >[ 6967.971094]  [<c1140595>] kobj_attr_store+0x16/0x22
>>> >> >[ 6967.971094]  [<c10d308e>] sysfs_write_file+0xc0/0xeb
>>> >> >[ 6967.971094]  [<c10d2fce>] ? sysfs_write_file+0x0/0xeb
>>> >> >[ 6967.971094]  [<c109511c>] vfs_write+0x80/0xdf
>>> >> >[ 6967.971094]  [<c109520f>] sys_write+0x3b/0x5d
>>> >> >[ 6967.971094]  [<c1002897>] sysenter_do_call+0x12/0x36
>>> >> >[ 6967.973262] CPU 1 is now offline
>>> >> >[ 6967.973271] lockdep: fixing up alternatives.
>>> >>
>>> >> Hmmm, does reverting commit 846f99749ab68b help?
>>> >>
>>> >
>>> > Of course it will help, but the problem is not that. That patch helps
>>> > us to detect such a problem... I am still investigating. :-/
>>> 
>>> This looks like this is triggered by a write to a sysfs file,
>>> so the solution is probably to call schedule_work so the
>>> suspend can happen outside the context of sysfs.
>>> 
>>> The typical scenario that triggers this is:
>>> - A lock is held while removing a sysfs attribute.
>>> - The same lock is grabbed inside the sysfs attribute.
>>> 
>>> I think we do that with the cpu_hotplug.lock
>>> 
>>> In this case it looks like this might be a reach around scenario where
>>> we try and remove the sysfs attribute that triggered the suspend.
>>
>> We don't do that.
>
>Looking at this a bit more.  Both this case and Arjuns (which is
>completely different chain of events) seem to have in common people
>removing sysfs attributes from within the contexts of a sysfs
>attribute.  As lockdep treats all instances of a lock as the same lock
>it appears to be picking up false positives.
>
>The classic mutex_lock_nested work around that introduces different lock
>classes can not be used directly here as the code is too deeply nested.
>
>The first problem this lockdep warning found was indeed a real and
>subtle bug, I think there are several other real bugs this annotation
>is capable of finding much easier than manual audits of the code, so I
>don't want to remove the lockdep annotations.
>
>Changing the cpu governor is especially interesting because it appears
>that this coming from a sysfs attribute that will be removed if/when
>the cpu is hotplug removed.  Which says to me that we really would like
>to have a couple of different lockdep classes in use, for essentially the
>same lock.
>
>So I think the thing to do is to add a lockdep subclass field to sysfs
>attributes so that we can take teach lockdep to distinguish between
>the handful of these that are safe because they are different instances
>of the same lock.
>
>How does the patch below look?
>
>From: Eric W. Biederman <ebiederm@...ssion.com>
>Date: Sun, 10 Jan 2010 18:13:35 -0800
>Subject: [PATCH] sysfs: Add support for lockdep subclasses to s_active
>
>We have apparently valid cases where the code for a sysfs attribute
>removes other sysfs attributes.  Without support for subclasses
>lockdep flags a possible recursive lock problem as it figures
>the first sysfs attribute could be attempting to remove itself.
>
>By adding support for sysfs subclasses we can teach lockdep to
>distinguish between different types of sysfs attributes and not
>get confused.
>
>Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>

Nice patch! :)

Reviewed-by: WANG Cong <xiyou.wangcong@...il.com>

Thank you!

>---
> fs/sysfs/dir.c        |   14 ++++++++++++--
> include/linux/sysfs.h |    7 +++++++
> kernel/power/power.h  |   15 ++++++++-------
> 3 files changed, 27 insertions(+), 9 deletions(-)
>
>diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
>index 5c4703d..c956931 100644
>--- a/fs/sysfs/dir.c
>+++ b/fs/sysfs/dir.c
>@@ -95,9 +95,14 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
>  */
> static struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
> {
>+	int subclass;
> 	if (unlikely(!sd))
> 		return NULL;
> 
>+	subclass = SYSFS_ATTR_NORMAL;
>+	if (sysfs_type(sd) == SYSFS_KOBJ_ATTR)
>+		subclass = sd->s_attr.attr->subclass;
>+
> 	while (1) {
> 		int v, t;
> 
>@@ -107,7 +112,7 @@ static struct sysfs_dirent *sysfs_get_active(struct sysfs_dirent *sd)
> 
> 		t = atomic_cmpxchg(&sd->s_active, v, v + 1);
> 		if (likely(t == v)) {
>-			rwsem_acquire_read(&sd->dep_map, 0, 1, _RET_IP_);
>+			rwsem_acquire_read(&sd->dep_map, subclass, 1, _RET_IP_);
> 			return sd;
> 		}
> 		if (t < 0)
>@@ -192,12 +197,17 @@ void sysfs_put_active_two(struct sysfs_dirent *sd)
> static void sysfs_deactivate(struct sysfs_dirent *sd)
> {
> 	DECLARE_COMPLETION_ONSTACK(wait);
>+	int subclass;
> 	int v;
> 
> 	BUG_ON(sd->s_sibling || !(sd->s_flags & SYSFS_FLAG_REMOVED));
> 	sd->s_sibling = (void *)&wait;
> 
>-	rwsem_acquire(&sd->dep_map, 0, 0, _RET_IP_);
>+	subclass = SYSFS_ATTR_NORMAL;
>+	if (sysfs_type(sd) == SYSFS_KOBJ_ATTR)
>+		subclass = sd->s_attr.attr->subclass;
>+
>+	rwsem_acquire(&sd->dep_map, subclass, 0, _RET_IP_);
> 	/* atomic_add_return() is a mb(), put_active() will always see
> 	 * the updated sd->s_sibling.
> 	 */
>diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
>index cfa8308..2f50fec 100644
>--- a/include/linux/sysfs.h
>+++ b/include/linux/sysfs.h
>@@ -20,6 +20,12 @@
> struct kobject;
> struct module;
> 
>+enum sysfs_attr_lock_class
>+{
>+	SYSFS_ATTR_NORMAL,
>+	SYSFS_ATTR_PM_CONTROL,
>+};
>+
> /* FIXME
>  * The *owner field is no longer used.
>  * x86 tree has been cleaned up. The owner
>@@ -29,6 +35,7 @@ struct attribute {
> 	const char		*name;
> 	struct module		*owner;
> 	mode_t			mode;
>+	enum sysfs_attr_lock_class	subclass;
> };
> 
> struct attribute_group {
>diff --git a/kernel/power/power.h b/kernel/power/power.h
>index 46c5a26..0459f27 100644
>--- a/kernel/power/power.h
>+++ b/kernel/power/power.h
>@@ -54,13 +54,14 @@ extern int hibernation_platform_enter(void);
> extern int pfn_is_nosave(unsigned long);
> 
> #define power_attr(_name) \
>-static struct kobj_attribute _name##_attr = {	\
>-	.attr	= {				\
>-		.name = __stringify(_name),	\
>-		.mode = 0644,			\
>-	},					\
>-	.show	= _name##_show,			\
>-	.store	= _name##_store,		\
>+static struct kobj_attribute _name##_attr = {		\
>+	.attr	= {					\
>+		.name = __stringify(_name),		\
>+		.mode = 0644,				\
>+		.subclass = SYSFS_ATTR_PM_CONTROL,	\
>+	},						\
>+	.show	= _name##_show,				\
>+	.store	= _name##_store,			\
> }
> 
> /* Preferred image size in bytes (default 500 MB) */
>-- 
>1.6.5.2.143.g8cc62
>
>

-- 
Live like a child, think like the god.
 
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