On 2014/12/26 15:01, Sasha Levin wrote: > On 12/26/2014 01:45 AM, Li Bin wrote: >> On 2014/7/8 4:05, Peter Zijlstra wrote: >>>> On Mon, Jul 07, 2014 at 09:55:43AM -0400, Sasha Levin wrote: >>>>>> I've also had this one, which looks similar: >>>>>> >>>>>> [10375.005884] BUG: spinlock recursion on CPU#0, modprobe/10965 >>>>>> [10375.006573] lock: 0xffff8803a0fd7740, .magic: dead4ead, .owner: >>>>>> modprobe/10965, .owner_cpu: 15 >>>>>> [10375.007412] CPU: 0 PID: 10965 Comm: modprobe Tainted: G W >>>>>> 3.16.0-rc3-next-20140704-sasha-00023-g26c0906-dirty #765 >>>> >>>> Something's fucked; so we have: >>>> >>>> debug_spin_lock_before() >>>> SPIN_BUG_ON(lock->owner == current, "recursion"); >>>> >> Hello, >> Does ACCESS_ONCE() can help this issue? I have no evidence that its lack is >> responsible for the issue, but I think here need it indeed. Is that right? >> >> SPIN_BUG_ON(ACCESS_ONCE(lock->owner) == current, "recursion"); > > Could you explain a bit more why do you think it's needed? >
Oh, just adding ACCESS_ONCE may be not enough, and i think lacking lock protection for reading lock->owner is a risk. In short, the reason of the issue is more like the spinlock debug mechanism, rather than a real spinlock recursion. ... //under no lock protection if (lock->owner == current) //access lock->owner |-spin_dump(lock, "recursion"); |-if (lock->owner && lock->owner != SPINLOCK_OWNER_INIT) //access lock->owner again owner = lock->owner; ... Right, or am I missing something? Thanks, Li Bin > > Thanks, > Sasha > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/