From: Roman Gushchin Date: Fri, 2 Nov 2018 22:47:49 +0000 (-0700) Subject: mm: handle no memcg case in memcg_kmem_charge() properly X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=e68599a3c3ad0f3171a7cb4e48aa6f9a69381902;p=openwrt%2Fstaging%2Fblogic.git mm: handle no memcg case in memcg_kmem_charge() properly Mike Galbraith reported a regression caused by the commit 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting") on a system with "cgroup_disable=memory" boot option: the system panics with the following stack trace: BUG: unable to handle kernel NULL pointer dereference at 00000000000000f8 PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT SMP PTI CPU: 0 PID: 1 Comm: systemd Not tainted 4.19.0-preempt+ #410 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20180531_142017-buildhw-08.phx2.fed4 RIP: 0010:page_counter_try_charge+0x22/0xc0 Code: 41 5d c3 c3 0f 1f 40 00 0f 1f 44 00 00 48 85 ff 0f 84 a7 00 00 00 41 56 48 89 f8 49 89 fe 49 Call Trace: try_charge+0xcb/0x780 memcg_kmem_charge_memcg+0x28/0x80 memcg_kmem_charge+0x8b/0x1d0 copy_process.part.41+0x1ca/0x2070 _do_fork+0xd7/0x3d0 do_syscall_64+0x5a/0x180 entry_SYSCALL_64_after_hwframe+0x49/0xbe The problem occurs because get_mem_cgroup_from_current() returns the NULL pointer if memory controller is disabled. Let's check if this is a case at the beginning of memcg_kmem_charge() and just return 0 if mem_cgroup_disabled() returns true. This is how we handle this case in many other places in the memory controller code. Link: http://lkml.kernel.org/r/20181029215123.17830-1-guro@fb.com Fixes: 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting") Signed-off-by: Roman Gushchin Reported-by: Mike Galbraith Acked-by: Rik van Riel Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Vladimir Davydov Cc: Shakeel Butt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 54920cbc46bf..6e1469b80cb7 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2593,7 +2593,7 @@ int memcg_kmem_charge(struct page *page, gfp_t gfp, int order) struct mem_cgroup *memcg; int ret = 0; - if (memcg_kmem_bypass()) + if (mem_cgroup_disabled() || memcg_kmem_bypass()) return 0; memcg = get_mem_cgroup_from_current();