On Mon, May 23, 2016 at 07:44:43PM +0200, Michal Hocko wrote: > On Mon 23-05-16 19:02:10, Vladimir Davydov wrote: > > mem_cgroup_oom may be invoked multiple times while a process is handling > > a page fault, in which case current->memcg_in_oom will be overwritten > > leaking the previously taken css reference. > > Have you seen this happening? I was under impression that the page fault > paths that have oom enabled will not retry allocations.
filemap_fault will, for readahead. This is rather unlikely, just like the whole oom scenario, so I haven't faced this leak in production yet, although it's pretty easy to reproduce using a contrived test. However, even if this leak happened on my host, I would probably not notice, because currently we have no clear means of catching css leaks. I'm thinking about adding a file to debugfs containing brief information about all memory cgroups, including dead ones, so that we could at least see how many dead memory cgroups are dangling out there. > > > Signed-off-by: Vladimir Davydov <[email protected]> > > That being said I do not have anything against the patch. It is a good > safety net I am just not sure this might happen right now and so the > patch is not stable candidate. > > After clarification > Acked-by: Michal Hocko <[email protected]> Thanks.
