linux-kernel - Re: NFS BUG_ON in nfs_do

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Date:	Sun, 26 Apr 2009 08:40:26 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Trond Myklebust <trond.myklebust@....uio.no>,
	linux-fsdevel@...r.kernel.org
Cc:	Rince <rincebrain@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: NFS BUG_ON in nfs_do_writepage

On Sat, Apr 25, 2009 at 10:57:08AM -0400, Trond Myklebust wrote:
> On Fri, 2009-04-24 at 05:26 -0400, Rince wrote:
> > Applied try 3 of Nick Piggin's patch to 2.6.30-rc3 (cleanly, no less!)
> > 
> > Doesn't appear to have helped at all - I received my favorite BUG ON
> > write.c:252 just like always, within 24 hours of booting the kernel,
> > even.
> 
> Can you apply the following incremental patch on top of Nick's. This
> appears to suffice to close the race on my setup.

Thanks, yes that looks good. Note: I deliberately didn't try to
convert filesystems because it needs much better understanding
of each one. So any fs maintainers using page_mkwrite I hope have
looked at these patches and considered whether they need to
do anything differently (ditto for the page_mkwrite return value
fixup patch).

Thanks,
Nick

> 
> Cheers
>   Trond
> ---------------------------------------------------------------------
> >From f0258852dcb43c748854d2ee550c9c270bb25f21 Mon Sep 17 00:00:00 2001
> From: Trond Myklebust <Trond.Myklebust@...app.com>
> Date: Fri, 24 Apr 2009 17:32:22 -0400
> Subject: [PATCH] NFS: Close page_mkwrite() races
> 
> Follow up to Nick Piggin's patches to ensure that nfs_vm_page_mkwrite
> returns with the page lock held, and sets the VM_FAULT_LOCKED flag.
> 
> Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
> ---
>  fs/nfs/file.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfs/file.c b/fs/nfs/file.c
> index 5a97bcf..ec7e27d 100644
> --- a/fs/nfs/file.c
> +++ b/fs/nfs/file.c
> @@ -517,10 +517,10 @@ static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  
>  	ret = nfs_updatepage(filp, page, 0, pagelen);
>  out_unlock:
> +	if (!ret)
> +		return VM_FAULT_LOCKED;
>  	unlock_page(page);
> -	if (ret)
> -		ret = VM_FAULT_SIGBUS;
> -	return ret;
> +	return VM_FAULT_SIGBUS;
>  }
>  
>  static struct vm_operations_struct nfs_file_vm_ops = {
> -- 
> 1.6.0.6
> 
> 
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