linux-kernel - Re: [PATCH] mm: do_generic_file_read() never gets a NULL 'filp' argument

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Message-Id: <20080922173703.C323.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Mon, 22 Sep 2008 17:40:24 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Krishna Kumar <krkumar2@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: do_generic_file_read() never gets a NULL 'filp' argument

> On Mon, 22 Sep 2008 11:46:10 +0530 Krishna Kumar <krkumar2@...ibm.com> wrote:
> 
> > From: Krishna Kumar <krkumar2@...ibm.com>
> > 
> > The 'filp' argument to do_generic_file_read() is never NULL.
> > 
> 
> How did you verify this?
> 
> NFS used to like passing NULL file*'s into VFS functions.  I don't
> recall whether it affected do_generic_file_read().

Andrew, current do_generic_file_read have filp dereference at the beginning of function.
So, I believe nobody pass to NULL.


static void do_generic_file_read(struct file *filp, loff_t *ppos,
                read_descriptor_t *desc, read_actor_t actor)
{
        struct address_space *mapping = filp->f_mapping;  /* here */
        struct inode *inode = mapping->host;
        struct file_ra_state *ra = &filp->f_ra;          /* ditto */
        pgoff_t index;
        pgoff_t last_index;
        pgoff_t prev_index;



> 
> >  mm/filemap.c |    3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff -ruNp 2.6.27-rc7-org/mm/filemap.c 2.6.27-rc7-new/mm/filemap.c
> > --- 2.6.27-rc7-org/mm/filemap.c	2008-09-17 12:53:25.000000000 +0530
> > +++ 2.6.27-rc7-new/mm/filemap.c	2008-09-17 12:53:59.000000000 +0530
> > @@ -1186,8 +1186,7 @@ out:
> >  	ra->prev_pos |= prev_offset;
> >  
> >  	*ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
> > -	if (filp)
> > -		file_accessed(filp);
> > +	file_accessed(filp);
> >  }
> >  
> >  int file_read_actor(read_descriptor_t *desc, struct page *page,
> --
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