Re: [PATCH v3] mm, memcg: fix error return value of mem_cgroup_css_alloc()

[Johannes Weiner <hannes@cmpxchg.org>]

On Mon, Apr 20, 2020 at 04:44:37PM -0700, Andrew Morton wrote:
> From: Yafang Shao <laoar.shao@gmail.com>
> Subject: mm, memcg: fix error return value of mem_cgroup_css_alloc()
> 
> When I run my memcg testcase which creates lots of memcgs, I found
> there're unexpected out of memory logs while there're still enough
> available free memory.  The error log is, mkdir: cannot create directory
> 'foo.65533': Cannot allocate memory
> 
> The reason is when we try to create more than MEM_CGROUP_ID_MAX memcgs, an
> -ENOMEM errno will be set by mem_cgroup_css_alloc(), but the right errno
> should be -ENOSPC "No space left on device", which is an appropriate errno
> for userspace's failed mkdir.
> 
> As the errno really misled me, we should make it right.  After this patch,
> the error log will be "mkdir: cannot create directory 'foo.65533': No
> space left on device"
> 
> [akpm@linux-foundation.org: s/EBUSY/ENOSPC/, per Michal]
> Link: http://lkml.kernel.org/r/20200407063621.GA18914@dhcp22.suse.cz
> Link: http://lkml.kernel.org/r/1586192163-20099-1-git-send-email-laoar.shao@gmail.com
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Acked-by: Michal Hocko <mhocko@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Fixes: 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure after many small jobs")
Acked-by: Johannes Weiner <hannes@cmpxchg.org>