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Date: Fri, 4 Aug 2017 11:16:29 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Wenwei Tao <wenwei.tww@alibaba-inc.com>,
        Oleg Nesterov <oleg@redhat.com>, David Rientjes <rientjes@google.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Re: [PATCH] mm, oom: fix potential data corruption when
 oom_reaper races with writer
Message-ID: <20170804091629.GI26029@dhcp22.suse.cz>
References: <201708040646.v746kkhC024636@www262.sakura.ne.jp>
 <20170804074212.GA26029@dhcp22.suse.cz>
 <201708040825.v748Pkul053862@www262.sakura.ne.jp>
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On Fri 04-08-17 17:25:46, Tetsuo Handa wrote:
> Well, while lockdep warning is gone, this problem is remaining.
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index edabf6f..1e06c29 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3931,15 +3931,14 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>         /*
>          * This mm has been already reaped by the oom reaper and so the
>          * refault cannot be trusted in general. Anonymous refaults would
> -        * lose data and give a zero page instead e.g. This is especially
> -        * problem for use_mm() because regular tasks will just die and
> -        * the corrupted data will not be visible anywhere while kthread
> -        * will outlive the oom victim and potentially propagate the date
> -        * further.
> +        * lose data and give a zero page instead e.g.
>          */
> -       if (unlikely((current->flags & PF_KTHREAD) && !(ret & VM_FAULT_ERROR)
> -                               && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags)))
> +       if (unlikely(!(ret & VM_FAULT_ERROR)
> +                    && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) {
> +               if (ret & VM_FAULT_RETRY)
> +                       down_read(&vma->vm_mm->mmap_sem);
>                 ret = VM_FAULT_SIGBUS;
> +       }
> 
>         return ret;
>  }

I have re-read your email again and I guess I misread previously. Are
you saying that the data corruption happens with the both patches
applied?

> 
> $ cat /tmp/file.* | od -b | head
> 0000000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 420330000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 420340000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 457330000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 457340000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs

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Date: Fri, 4 Aug 2017 11:16:29 +0200
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: Re: [PATCH] mm, oom: fix potential data corruption when
 oom_reaper races with writer
Message-ID: <20170804091629.GI26029@dhcp22.suse.cz>
References: <201708040646.v746kkhC024636@www262.sakura.ne.jp>
 <20170804074212.GA26029@dhcp22.suse.cz>
 <201708040825.v748Pkul053862@www262.sakura.ne.jp>
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Wenwei Tao <wenwei.tww@alibaba-inc.com>, Oleg Nesterov <oleg@redhat.com>, David Rientjes <rientjes@google.com>, LKML <linux-kernel@vger.kernel.org>

On Fri 04-08-17 17:25:46, Tetsuo Handa wrote:
> Well, while lockdep warning is gone, this problem is remaining.
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index edabf6f..1e06c29 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3931,15 +3931,14 @@ int handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
>         /*
>          * This mm has been already reaped by the oom reaper and so the
>          * refault cannot be trusted in general. Anonymous refaults would
> -        * lose data and give a zero page instead e.g. This is especially
> -        * problem for use_mm() because regular tasks will just die and
> -        * the corrupted data will not be visible anywhere while kthread
> -        * will outlive the oom victim and potentially propagate the date
> -        * further.
> +        * lose data and give a zero page instead e.g.
>          */
> -       if (unlikely((current->flags & PF_KTHREAD) && !(ret & VM_FAULT_ERROR)
> -                               && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags)))
> +       if (unlikely(!(ret & VM_FAULT_ERROR)
> +                    && test_bit(MMF_UNSTABLE, &vma->vm_mm->flags))) {
> +               if (ret & VM_FAULT_RETRY)
> +                       down_read(&vma->vm_mm->mmap_sem);
>                 ret = VM_FAULT_SIGBUS;
> +       }
> 
>         return ret;
>  }

I have re-read your email again and I guess I misread previously. Are
you saying that the data corruption happens with the both patches
applied?

> 
> $ cat /tmp/file.* | od -b | head
> 0000000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 420330000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 420340000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 457330000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
> *
> 457340000 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377 377
> *
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>