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Message-ID: <20090912133944.GB5858@ZenIV.linux.org.uk>
Date: Sat, 12 Sep 2009 14:39:44 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Dave Hansen <dave@...ux.vnet.ibm.com>
Cc: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
akpm <akpm@...uxfoundation.org>
Subject: Re: mnt_want_write_file() has problem?
On Tue, Aug 04, 2009 at 12:15:19PM -0700, Dave Hansen wrote:
> On Mon, 2009-08-03 at 06:36 +0900, OGAWA Hirofumi wrote:
> > diff -puN fs/namespace.c~mnt_want_write-wrong-assume fs/namespace.c
> > ---
> > linux-2.6/fs/namespace.c~mnt_want_write-wrong-assume 2009-08-03
> > 04:33:35.000000000 +0900
> > +++ linux-2.6-hirofumi/fs/namespace.c 2009-08-03 04:31:34.000000000
> > +0900
> > @@ -316,7 +316,8 @@ EXPORT_SYMBOL_GPL(mnt_clone_write);
> > */
> > int mnt_want_write_file(struct file *file)
> > {
> > - if (!(file->f_mode & FMODE_WRITE))
> > + struct inode *inode = file->f_dentry->d_inode;
> > + if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
> > return mnt_want_write(file->f_path.mnt);
> > else
> > return mnt_clone_write(file->f_path.mnt);
>
> I'm fine with this. I'd like a debugging check in mnt_clone_write()
> since this bug is easy to detect, but such a check will also cost all of
> the performance gains that Nick added. So, we can't have it
> unconditionally.
[Very belated] ACK.
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