On 10/4/15 04:09, Richard Weinberger wrote:
> With that change you're reintroducing an issue.
> Please see:
> commit 7cd5a02f54f4c9d16cf7fdffa2122bc73bb09b43
> Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Date: Mon Aug 11 09:30:25 2008 +0200
>
> mm: fix mm_take_all_locks() locking order
>
> Lockdep spotted:
>
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.27-rc1 #270
> -------------------------------------------------------
> qemu-kvm/2033 is trying to acquire lock:
> (&inode->i_data.i_mmap_lock){----}, at: [<ffffffff802996cc>]
> mm_take_all_locks+0xc2/0xea
>
> but task is already holding lock:
> (&anon_vma->lock){----}, at: [<ffffffff8029967a>]
> mm_take_all_locks+0x70/0xea
>
> which lock already depends on the new lock.
>
Oh, really. Thanks.
>
> git blame often explains funky code. :-)
>
Next, I shall check the git log before make patches, each time. :-)
Theoretically, the lock and unlock need to be symmetric, if we have to
lock f_mapping all firstly, then lock all anon_vma, probably, we also
need to unlock anon_vma all, then unlock all f_mapping.
Thanks.
--
Chen Gang (陈刚)
Open, share, and attitude like air, water, and life which God blessed
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