linux-kernel - Re: [PATCH v3 5/8] proc/kcore: hold lock during read

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Date:   Wed, 25 Jul 2018 16:34:11 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        James Morse <james.morse@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>, kernel-team@...com
Subject: Re: [PATCH v3 5/8] proc/kcore: hold lock during read

On Wed, Jul 25, 2018 at 12:11:26AM +0900, Tetsuo Handa wrote:
> On 2018/07/19 7:58, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@...com>
> > 
> > Now that we're using an rwsem, we can hold it during the entirety of
> > read_kcore() and have a common return path. This is preparation for the
> > next change.
> > 
> > Signed-off-by: Omar Sandoval <osandov@...com>
> > ---
> >  fs/proc/kcore.c | 70 ++++++++++++++++++++++++++++---------------------
> >  1 file changed, 40 insertions(+), 30 deletions(-)
> > 
> > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> > index 95aa988c5b5d..e317ac890871 100644
> > --- a/fs/proc/kcore.c
> > +++ b/fs/proc/kcore.c
> > @@ -440,19 +440,18 @@ static ssize_t
> >  read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
> >  {
> >  	char *buf = file->private_data;
> > -	ssize_t acc = 0;
> >  	size_t size, tsz;
> >  	size_t elf_buflen;
> >  	int nphdr;
> >  	unsigned long start;
> > +	size_t orig_buflen = buflen;
> > +	int ret = 0;
> >  
> >  	down_read(&kclist_lock);
> 
> (...snipped...)
> 
> > +out:
> > +	up_write(&kclist_lock);
> 
> Oops. This needs to be up_read().

Yeah, thanks, I'll fix this and rerun my tests with lockdep.