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Date: Fri, 05 Feb 2010 14:33:20 +0800
From: Cong Wang <amwang@redhat.com>
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To: linux-kernel@vger.kernel.org
CC: Tejun Heo <tj@kernel.org>, Greg Kroah-Hartman <gregkh@suse.de>,
       Peter Zijlstra <peterz@infradead.org>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Miles Lane <miles.lane@gmail.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Larry Finger <Larry.Finger@lwfinger.net>, akpm@linux-foundation.org
Subject: Re: [Patch] sysfs: add lockdep class support to s_active
References: <20100205062814.4119.53209.sendpatchset@localhost.localdomain>
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Amerigo Wang wrote:
> Recently we met a lockdep warning from sysfs during s2ram or cpu hotplug.
> As reported by several people, it is something like:
> 
> [ 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
> [...]
> 
> Eric already provides a patch for this[1], but it still can't fix the
> problem. Based on his work and Peter's suggestion, I write this patch,
> hopefully we can fix the warning completely.
> 
> This patch put sysfs s_active into two classes, one is for PM, the other
> is for the rest, so lockdep will distinguish them.
> 
> 1. http://lkml.org/lkml/2010/1/10/282
> 
> 
> Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
> Reported-by: Miles Lane <miles.lane@gmail.com>
> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> Signed-off-by: WANG Cong <amwang@redhat.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> 
> 
> ---
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index dc30d9e..72a8d0b 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -24,6 +24,8 @@
>  
>  #include "sysfs.h"
>  
> +static struct lock_class_key sysfs_classes[SYSFS_NR_CLASSES];
> +
>  /* used in crash dumps to help with debugging */
>  static char last_sysfs_file[PATH_MAX];
>  void sysfs_printk_last_file(void)
> @@ -504,11 +506,16 @@ int sysfs_add_file_mode(struct sysfs_dirent *dir_sd,
>  	struct sysfs_addrm_cxt acxt;
>  	struct sysfs_dirent *sd;
>  	int rc;
> +	int class;
>  
>  	sd = sysfs_new_dirent(attr->name, mode, type);
>  	if (!sd)
>  		return -ENOMEM;
>  	sd->s_attr.attr = (void *)attr;
> +	class = SYSFS_ATTR_NORMAL;
> +	if (sysfs_type(sd) == SYSFS_KOBJ_ATTR)
> +		class = sd->s_attr.attr->class;
> +	lockdep_set_class(&sd->s_active, &sysfs_classes[class]);
>  

Oops! I missed one part, please ignore this patch...