Re: [PATCH 2/5] fs: charge pipe buffers to memcg

From	Vladimir Davydov <vdavydov@virtuozzo.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/5] fs: charge pipe buffers to memcg
Date	2015-09-30 19:00 +0200
Message-ID	<qesTw-2qP-1@gated-at.bofh.it> (permalink)
References	<qcVdg-5WW-5@gated-at.bofh.it> <qcVdg-5WW-7@gated-at.bofh.it> <qec2m-3qN-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Tue, Sep 29, 2015 at 03:57:11PM -0700, Andrew Morton wrote:
> On Sat, 26 Sep 2015 13:45:54 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:
> 
> > Pipe buffers can be generated unrestrictedly by an unprivileged
> > userspace process, so they shouldn't go unaccounted.
> > 
> > ...
> >
> > --- a/fs/pipe.c
> > +++ b/fs/pipe.c
> > @@ -400,7 +400,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
> >  			int copied;
> >  
> >  			if (!page) {
> > -				page = alloc_page(GFP_HIGHUSER);
> > +				page = alloc_kmem_pages(GFP_HIGHUSER, 0);
> >  				if (unlikely(!page)) {
> >  					ret = ret ? : -ENOMEM;
> >  					break;
> 
> This seems broken.  We have a page buffer page which has a weird
> ->mapcount.  Now it gets stolen (generic_pipe_buf_steal()) and spliced
> into pagecache.  Then the page gets mmapped and MM starts playing with
> its ->_mapcount?

Right you are! I completely forgot of vmsplice case. Surely, we need to
uncharge the page in the ->steal method and clear its PageKmem. Will fix
that.

Thanks,
Vladimir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 2/5] fs: charge pipe buffers to memcg Vladimir Davydov <vdavydov@parallels.com> - 2015-09-26 12:50 +0200
  Re: [PATCH 2/5] fs: charge pipe buffers to memcg Andrew Morton <akpm@linux-foundation.org> - 2015-09-30 01:00 +0200
    Re: [PATCH 2/5] fs: charge pipe buffers to memcg Vladimir Davydov <vdavydov@virtuozzo.com> - 2015-09-30 19:00 +0200

csiph-web