Re: [PATCH] Possible race in sysfs_read_file() and sysfs_write_file()

[Simon Derr]

On Fri, 3 Sep 2004, Simon Derr wrote:

> On Thu, 2 Sep 2004, Andrew Morton wrote:
>
> > Simon Derr <Simon.Derr@xxxxxxxx> wrote:
> > >
> > > @@ -140,13 +145,17 @@
> > >   	struct sysfs_buffer * buffer = file->private_data;
> > >   	ssize_t retval = 0;
> > >
> > >  -	if (!*ppos) {
> > >  +	down(&buffer->sem);
> > >  +	if ((!*ppos) || (!buffer->page)) {
> > >   		if ((retval = fill_read_buffer(file->f_dentry,buffer)))
> > >  -			return retval;
> > >  +			goto out;
> >
> > Why are we testing *ppos at all in here?
>
> And if we open a sysfs file with O_RDWR, and write() into it, then this is
> needed if we want to read(), because else the buffer will have been
> allocated, but ops->show() not called. I'm not too sure about this being
> useful either.

Hmmm...
We are still screwed if we read at offset >0 after a write.

Possible fix would be to add a 'dirty' flag to the sysfs_buffer when
write() is called, so we force a call to fill_read_buffer() on the next
read().

Or maybe simply forbid O_RDWR open() ? Are they of any use ?
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