Messages in this thread | | | Date | Fri, 5 Feb 2010 18:00:59 +0800 | Subject | Re: [Patch v2] sysfs: add lockdep class support to s_active | From | Xiaotian Feng <> |
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On Fri, Feb 5, 2010 at 5:39 PM, Eric W. Biederman <ebiederm@xmission.com> wrote: > Xiaotian Feng <xtfeng@gmail.com> writes: > >> On Fri, Feb 5, 2010 at 2:42 PM, Amerigo Wang <amwang@redhat.com> 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. >> >> I think this patch does not hit the root cause, we have a similiar >> warning which is not related with PM. > > The root cause is that our locking is crazy complicated. No lockdep > changes are going to fix that. > > What we can do and what the patch does is teach lockdep to treat some > of the sysfs files as a different group (subclass) from other sysfs > files. Which keeps us from overgeneralizing too much and having > a better signal to noise ratio. > > As for the block device problem goes, I can't easily say that > the block layer is correct. I expect it is because changing > the scheduler is unlikely to delete block devices. If the block layer > has bugs then adding another subclass as Amerigo suggests should simply > make lockdep warnings harder to trigger and more accurate so that > sounds like a path worth walking. > > In general I recommend that pieces of code that need to do a lot of > work in a sysfs attribute consider using a work queue or a kernel > thread, as that can be easier to analyze.
PM case store /sys/devices/system/cpu1/online remove /sys/devices/system/cpu1/cache/
iosched case store /sys/block/sdx/queue/scheduler remove /sys/block/sdx/queue/iosched/
So it looks like this is from sysfs layer ....
> > Eric > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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