Re: [PATCH 2/4] fsfreeze: added new file_start_write_killable

[Marco Stornelli]

Hi,

Il 26/04/2013 14:06, Matthew Wilcox ha scritto:
> On Fri, Apr 26, 2013 at 10:50:52AM +0200, Marco Stornelli wrote:
> > Replace file_start_write with file_start_write_killable where
> > possible.
>
> I feel like I'm missing context here.  Possibly because you only cc'd me
> on patch 2/4.  In particular, file_start_write doesn't exist upstream,
> so I'm not sure what it's for.  But returning 1 for non-regular files
> looks dodgy:

The patch series is based on -next due to several changes done by Al 
about fsfreeze. file_start_write_killable returns 1 because it's mainly 
a wrapper of __st_start_write. __sb_start_write returns 1 when 
everything is ok, 0 when the lock can't be gotten (we are using the 
trylock version) and _now_ a value < 0 when something happens (i.e. -EINTR).

> > +static inline int file_start_write_killable(struct file *file)
> > +{
> > +	if (!S_ISREG(file_inode(file)->i_mode))
> > +		return 1;
> > +	return sb_start_write_killable(file_inode(file)->i_sb);
> > +}
>
> > +++ b/fs/aio.c
> > @@ -1103,8 +1103,11 @@ static ssize_t aio_rw_vect_retry(struct kiocb *iocb, int rw, aio_rw_op *rw_op)
> >   	if (iocb->ki_pos < 0)
> >   		return -EINVAL;
> >
> > -	if (rw == WRITE)
> > -		file_start_write(file);
> > +	if (rw == WRITE) {
> > +		ret = file_start_write_killable(file);
> > +		if (ret < 0)
> > +			return ret;
> > +	}
> >   	do {
>
> So ... it's OK to do this write to pipes/directories/devices/... ?  Or is
> that check always taken care of elsewhere?  If so, why do we need this
> check?  I'm confused.  None of the callers check for the 'ret == 1' case,
> so I'm sure there's something wrong here, I just can't tell what it is.

See above.

> > +++ b/fs/read_write.c
> > @@ -438,17 +438,19 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_
> >   	ret = rw_verify_area(WRITE, file, pos, count);
> >   	if (ret >= 0) {
> >   		count = ret;
> > -		file_start_write(file);
> > -		if (file->f_op->write)
> > -			ret = file->f_op->write(file, buf, count, pos);
> > -		else
> > -			ret = do_sync_write(file, buf, count, pos);
> > +		ret = file_start_write_killable(file);
> >   		if (ret > 0) {
> > -			fsnotify_modify(file);
> > -			add_wchar(current, ret);
> > +			if (file->f_op->write)
> > +				ret = file->f_op->write(file, buf, count, pos);
> > +			else
> > +				ret = do_sync_write(file, buf, count, pos);
> > +			if (ret > 0) {
> > +				fsnotify_modify(file);
> > +				add_wchar(current, ret);
> > +			}
> > +			inc_syscw(current);
> > +			file_end_write(file);
> >   		}
> > -		inc_syscw(current);
> > -		file_end_write(file);
> >   	}
> >
> >   	return ret;
>
> I don't like it that you've increased the indentation here.  Better to do
> a preliminary patch which just converts to our normal style with gotos.  ie:

Ok, I can change the style here, no problem.

Marco
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