linux-kernel - Re: [PATCH 1/3] vmalloc: ignore vmalloc area holes in vwrite()

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Date:	Tue, 15 Sep 2009 13:21:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Christoph Lameter <clameter@....com>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] vmalloc: ignore vmalloc area holes in vwrite()

On Tue, Sep 15, 2009 at 11:18:29AM +0800, KAMEZAWA Hiroyuki wrote:
> On Tue, 15 Sep 2009 11:15:07 +0800
> Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > Hi Kame,
> > 
> > I'll go out for a while. If you are going to do your improvements to
> > vmalloc.c, please feel free to do so. I can rebase the hwpoison bits
> > after yours.
> > 
> > I could do the kmem part(in a modified patch 2/3) and let it return
> > any error code vread/vwrite reports.  Ideally the kmem read/write
> > could do
> > 
> >         if (zero bytes successfully read/written)
> >                 return error_code;
> >         else
> >                 return bytes_so_far;
> > 
> > Do you agree?
> > 
> Okay. I'll write patches for vread/vwrite. And make them just return bool.

bool may not be sufficient? For obviously you need to return -EFAULT
for invalid address and I need to return -EIO for hwpoison pages.
(I assume you put is_vmalloc_or_module_addr() immediately before the
vmalloc_to_page() calls in vmalloc.c, which seems a more natural place
than in mem.c.)

Thanks,
Fengguang

>  true .....requested area includes valid memory range and worth to be copied.
>  false.....no valid range found.
> 
> Thanks,
> -Kame
> 
> 
> 
> 
> > Thanks,
> > Fengguang
> > 
> > On Tue, Sep 15, 2009 at 10:34:25AM +0800, KAMEZAWA Hiroyuki wrote:
> > > On Tue, 15 Sep 2009 10:18:52 +0800
> > > Wu Fengguang <fengguang.wu@...el.com> wrote:
> > > 
> > > > Siliently ignore all vmalloc area holes in vwrite(),
> > > > and report success to the caller even if nothing is written.
> > > > 
> > > > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > > > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > > 
> > > Why don't you modify vread() at the same time ?
> > > Because /proc/kcore ignores return value of vread(), I think you can
> > > modify it without no side-effect.
> > > 
> > > Regards,
> > > -Kame
> > > 
> > > > ---
> > > >  mm/vmalloc.c |   13 ++-----------
> > > >  1 file changed, 2 insertions(+), 11 deletions(-)
> > > > 
> > > > --- linux-mm.orig/mm/vmalloc.c	2009-09-15 10:08:33.000000000 +0800
> > > > +++ linux-mm/mm/vmalloc.c	2009-09-15 10:14:18.000000000 +0800
> > > > @@ -1805,10 +1805,8 @@ finished:
> > > >   *	@addr:		vm address.
> > > >   *	@count:		number of bytes to be read.
> > > >   *
> > > > - *	Returns # of bytes which addr and buf should be incresed.
> > > > + *	Returns # of bytes which addr and buf should be increased.
> > > >   *	(same number to @count).
> > > > - *	If [addr...addr+count) doesn't includes any intersect with valid
> > > > - *	vmalloc area, returns 0.
> > > >   *
> > > >   *	This function checks that addr is a valid vmalloc'ed area, and
> > > >   *	copy data from a buffer to the given addr. If specified range of
> > > > @@ -1816,8 +1814,6 @@ finished:
> > > >   *	proper area of @buf. If there are memory holes, no copy to hole.
> > > >   *	IOREMAP area is treated as memory hole and no copy is done.
> > > >   *
> > > > - *	If [addr...addr+count) doesn't includes any intersects with alive
> > > > - *	vm_struct area, returns 0.
> > > >   *	@buf should be kernel's buffer. Because	this function uses KM_USER0,
> > > >   *	the caller should guarantee KM_USER0 is not used.
> > > >   *
> > > > @@ -1834,7 +1830,6 @@ long vwrite(char *buf, char *addr, unsig
> > > >  	struct vm_struct *tmp;
> > > >  	char *vaddr;
> > > >  	unsigned long n, buflen;
> > > > -	int copied = 0;
> > > >  
> > > >  	/* Don't allow overflow */
> > > >  	if ((unsigned long) addr + count < count)
> > > > @@ -1856,18 +1851,14 @@ long vwrite(char *buf, char *addr, unsig
> > > >  		n = vaddr + tmp->size - PAGE_SIZE - addr;
> > > >  		if (n > count)
> > > >  			n = count;
> > > > -		if (!(tmp->flags & VM_IOREMAP)) {
> > > > +		if (!(tmp->flags & VM_IOREMAP))
> > > >  			aligned_vwrite(buf, addr, n);
> > > > -			copied++;
> > > > -		}
> > > >  		buf += n;
> > > >  		addr += n;
> > > >  		count -= n;
> > > >  	}
> > > >  finished:
> > > >  	read_unlock(&vmlist_lock);
> > > > -	if (!copied)
> > > > -		return 0;
> > > >  	return buflen;
> > > >  }
> > > >  
> > > > 
> > > > -- 
> > > > 
> > > > 
> > 
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