Re: [Patch 0/2] sysfs: fix s_active lockdep warning

From: Cong Wang
Date: Fri Jan 29 2010 - 03:36:09 EST

Eric W. Biederman wrote:
Amerigo Wang <amwang@xxxxxxxxxx> writes:

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>]
[ 6967.970493]
[ 6967.970497] but task is already holding lock:
[ 6967.970506] (s_active){++++.+}, at: [<c10d4110>]

Eric already provides a patch for this[1], but it still can't fix the
problem. I add the missing part of Eric's patch and send these two patches
together, hopefully we can fix the warning completely.


Reported-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Reported-by: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
Reported-by: Miles Lane <miles.lane@xxxxxxxxx>
Reported-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxx>

Thanks for following up on this.

I suspect we may want to create a separate class for each sysfs file
instead of playing whack-a-mole and creating a subclass each time we
have problems.

I don't see why the rules for one sysfs file should be the same as for
any other sysfs file.

I am confused, we don't know who created sysfs files unless we
separate them by subclasses, the way of your patch is very straight

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