On Sat, Oct 3, 2015 at 9:38 PM, Chen Gang <xili_gchen_5257@xxxxxxxxxxx> wrote:
> From 36dbcc145819655682f80efd49e72b01515b4e9a Mon Sep 17 00:00:00 2001
> From: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
> Date: Sun, 4 Oct 2015 03:22:41 +0800
> Subject: [PATCH] mm/mmap.c: Remove redundant vma looping
>
> vma->vm_file->f_mapping and vma->anon_vma are shared with the same vma
> looping, so merge them.
>
> Signed-off-by: Chen Gang <gang.chen.5i5j@xxxxxxxxx>
> ---
> mm/mmap.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 8393580..f7c1631 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3201,9 +3201,7 @@ int mm_take_all_locks(struct mm_struct *mm)
> goto out_unlock;
> if (vma->vm_file && vma->vm_file->f_mapping)
> vm_lock_mapping(mm, vma->vm_file->f_mapping);
> - }
>
> - for (vma = mm->mmap; vma; vma = vma->vm_next) {
> if (signal_pending(current))
> goto out_unlock;
> if (vma->anon_vma)
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.
git blame often explains funky code. :-)
--
Thanks,
//richard
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