Messages in this thread | | | Date | Tue, 24 May 2016 19:13:36 +0300 | From | Vladimir Davydov <> | Subject | Re: [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; > > +}
| |