Re: [PATCH] fs/seq_file: Fix warning of passing zero to 'PTR_ERR'

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Dec 07, 2017 at 11:23:26PM +0000, Al Viro wrote:
> On Fri, Dec 08, 2017 at 12:03:07AM +0100, Vasyl Gomonovych wrote:
> > p could be NULL and passing into PTR_ERR
> > 
> > Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
> > ---
> >  fs/seq_file.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/seq_file.c b/fs/seq_file.c
> > index 4be761c..8b700b9 100644
> > --- a/fs/seq_file.c
> > +++ b/fs/seq_file.c
> > @@ -262,8 +262,8 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
> >  		size_t offs = m->count;
> >  		loff_t next = pos;
> >  		p = m->op->next(m, p, &next);
> > -		if (!p || IS_ERR(p)) {
> > -			err = PTR_ERR(p);
> > +		if (IS_ERR(p)) {
> > +			err = (!p ? -EFAULT : PTR_ERR(p));
> 
> What does it fix, if I might ask?  And while we are at it, would
> you mind explaining the reasoning behind that change?  Or, say,
> testing done to it...

While we are at it, where has that -EFAULT come from?  And how
would it be ever reached, seeing that IS_ERR(NULL) is false?