lkml.org 
[lkml]   [2016]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RESEND 7/8] pipe: account to kmemcg
On Tue, May 24, 2016 at 05:59:02AM -0700, Eric Dumazet wrote:
...
> > +static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
> > + struct pipe_buffer *buf)
> > +{
> > + struct page *page = buf->page;
> > +
> > + if (page_count(page) == 1) {
>
> This looks racy : some cpu could have temporarily elevated page count.

All pipe operations (pipe_buf_operations->get, ->release, ->steal) are
supposed to be called under pipe_lock. So, if we see a pipe_buffer->page
with refcount of 1 in ->steal, that means that we are the only its user
and it can't be spliced to another pipe.

In fact, I just copied the code from generic_pipe_buf_steal, adding
kmemcg related checks along the way, so it should be fine.

Thanks,
Vladimir

>
> > + if (memcg_kmem_enabled()) {
> > + memcg_kmem_uncharge(page, 0);
> > + __ClearPageKmemcg(page);
> > + }
> > + __SetPageLocked(page);
> > + return 0;
> > + }
> > + return 1;
> > +}

\
 
 \ /
  Last update: 2016-05-24 19:01    [W:0.056 / U:0.692 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site