On Wed, 20 Jul 2011, Peter Zijlstra wrote:
just hit the following with full debuging turned on:
| =============================================
| [ INFO: possible recursive locking detected ]
| 3.0.0-rc7-00088-g1765a36 #64
| ---------------------------------------------
| udevd/1054 is trying to acquire lock:
| (&(&parent->list_lock)->rlock){..-...}, at: [<c00bf640>] cache_alloc_refill+0xac/0x868
|
| but task is already holding lock:
| (&(&parent->list_lock)->rlock){..-...}, at: [<c00be47c>] cache_flusharray+0x58/0x148
|
| other info that might help us debug this:
| Possible unsafe locking scenario:
|
| CPU0
| ----
| lock(&(&parent->list_lock)->rlock);
| lock(&(&parent->list_lock)->rlock);
On Sun, 17 Jul 2011, Thomas Gleixner wrote:
Known problem. Pekka is looking into it.
Actually, I kinda was hoping Peter would make it go away. ;-)
Looking at the lockdep report, it's l3->list_lock and I really don't quite
understand why it started to happen now. There hasn't been any major
changes in mm/slab.c for a while. Did lockdep become more strict recently?
Not that I know.. :-) I bet -rt just makes it easier to trigger this
weirdness.
Let me try and look at slab.c without my eyes burning out.. I so hate
that code.
So what exactly is the lockdep complaint above telling us? We're holding
on to l3->list_lock in cache_flusharray() (kfree path) but somehow we now
entered cache_alloc_refill() (kmalloc path!) and attempt to take the same
lock or lock in the same class.
I am confused. How can that happen?
Pekka
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