Messages in this thread | | | Subject | Re: [Patch 0/2] sysfs: fix s_active lockdep warning | From | (Eric W. Biederman) | Date | Fri, 29 Jan 2010 05:44:07 -0800 |
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Cong Wang <amwang@redhat.com> writes:
> Eric W. Biederman wrote: >> Amerigo Wang <amwang@redhat.com> 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>] >>> 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. I add the missing part of Eric's patch and send these two patches >>> together, hopefully we can fix the warning completely. >>> >>> 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> >>> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> >>> Cc: Tejun Heo <tj@kernel.org> >>> Cc: Greg Kroah-Hartman <gregkh@suse.de> >> >> 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 > ward.
The assumption is that all entities in a class are used very similarly. What I was suggesting is that it may make sense, and be simpler to have a separate __key value and thus place each sysfs file in it's class.
Doing that is a lot more for lockdep to track, but it would not produce the confusing false positives that we see now. From the reports I have seen we may have more that 16 subclasses in sysfs, and it will likely take us a while to find them all.
Eric
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