+ mm-cgroup-avoid-panic-when-init-with-low-memory.patch added to -mm tree

+ mm-cgroup-avoid-panic-when-init-with-low-memory.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm/cgroup: avoid panic when init with low memory
has been added to the -mm tree.  Its filename is
     mm-cgroup-avoid-panic-when-init-with-low-memory.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-cgroup-avoid-panic-when-init-with-low-memory.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-cgroup-avoid-panic-when-init-with-low-memory.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Subject: mm/cgroup: avoid panic when init with low memory

The system may panic when initialisation is done when almost all the
memory is assigned to the huge pages using the kernel command line
parameter hugepage=xxxx.  Panic may occur like this:

[    0.082289] Unable to handle kernel paging request for data at address 0x00000000
[    0.082338] Faulting instruction address: 0xc000000000302b88
[    0.082377] Oops: Kernel access of bad area, sig: 11 [#1]
[    0.082408] SMP NR_CPUS=2048 [    0.082424] NUMA
[    0.082440] pSeries
[    0.082457] Modules linked in:
[    0.082490] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.9.0-15-generic #16-Ubuntu
[    0.082536] task: c00000021ed01600 task.stack: c00000010d108000
[    0.082575] NIP: c000000000302b88 LR: c000000000270e04 CTR: c00000000016cfd0
[    0.082621] REGS: c00000010d10b2c0 TRAP: 0300   Not tainted (4.9.0-15-generic)
[    0.082666] MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE>[ 0.082770]   CR: 28424422  XER: 00000000
[    0.082793] CFAR: c0000000003d28b8 DAR: 0000000000000000 DSISR: 40000000 SOFTE: 1
GPR00: c000000000270e04 c00000010d10b540 c00000000141a300 c00000010fff6300
GPR04: 0000000000000000 00000000026012c0 c00000010d10b630 0000000487ab0000
GPR08: 000000010ee90000 c000000001454fd8 0000000000000000 0000000000000000
GPR12: 0000000000004400 c00000000fb80000 00000000026012c0 00000000026012c0
GPR16: 00000000026012c0 0000000000000000 0000000000000000 0000000000000002
GPR20: 000000000000000c 0000000000000000 0000000000000000 00000000024200c0
GPR24: c0000000016eef48 0000000000000000 c00000010fff7d00 00000000026012c0
GPR28: 0000000000000000 c00000010fff7d00 c00000010fff6300 c00000010d10b6d0
NIP [c000000000302b88] mem_cgroup_soft_limit_reclaim+0xf8/0x4f0
[    0.083456] LR [c000000000270e04] do_try_to_free_pages+0x1b4/0x450
[    0.083494] Call Trace:
[    0.083511] [c00000010d10b540] [c00000010d10b640] 0xc00000010d10b640 (unreliable)
[    0.083567] [c00000010d10b610] [c000000000270e04] do_try_to_free_pages+0x1b4/0x450
[    0.083622] [c00000010d10b6b0] [c000000000271198] try_to_free_pages+0xf8/0x270
[    0.083676] [c00000010d10b740] [c000000000259dd8] __alloc_pages_nodemask+0x7a8/0xff0
[    0.083729] [c00000010d10b960] [c0000000002dd274] new_slab+0x104/0x8e0
[    0.083776] [c00000010d10ba40] [c0000000002e03d0] ___slab_alloc+0x620/0x700
[    0.083822] [c00000010d10bb70] [c0000000002e04e4] __slab_alloc+0x34/0x60
[    0.083868] [c00000010d10bba0] [c0000000002e101c] kmem_cache_alloc_node_trace+0xdc/0x310
[    0.083947] [c00000010d10bc00] [c000000000eb8120] mem_cgroup_init+0x158/0x1c8
[    0.083994] [c00000010d10bc40] [c00000000000dde8] do_one_initcall+0x68/0x1d0
[    0.084041] [c00000010d10bd00] [c000000000e84184] kernel_init_freeable+0x278/0x360
[    0.084094] [c00000010d10bdc0] [c00000000000e714] kernel_init+0x24/0x170
[    0.084143] [c00000010d10be30] [c00000000000c0e8] ret_from_kernel_thread+0x5c/0x74
[    0.084195] Instruction dump:
[    0.084220] eb81ffe0 eba1ffe8 ebc1fff0 ebe1fff8 4e800020 3d230001 e9499a42 3d220004
[    0.084300] 3929acd8 794a1f24 7d295214 eac90100 <e9360000> 2fa90000 419eff74 3b200000
[    0.084382] ---[ end trace 342f5208b00d01b6 ]---

This is a chicken and egg issue where the kernel try to get free memory
when allocating per node data in mem_cgroup_init(), but in that path
mem_cgroup_soft_limit_reclaim() is called which assumes that these data
are allocated.

As mem_cgroup_soft_limit_reclaim() is best effort, it should return when
these data are not yet allocated.

This patch also fixes potential null pointer access in
mem_cgroup_remove_from_trees() and mem_cgroup_update_tree().

Link: http://lkml.kernel.org/r/1487856999-16581-2-git-send-email-ldufour@linux.vnet.ibm.com
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff -puN mm/memcontrol.c~mm-cgroup-avoid-panic-when-init-with-low-memory mm/memcontrol.c
--- a/mm/memcontrol.c~mm-cgroup-avoid-panic-when-init-with-low-memory
+++ a/mm/memcontrol.c
@@ -465,6 +465,8 @@ static void mem_cgroup_update_tree(struc
 	struct mem_cgroup_tree_per_node *mctz;
 
 	mctz = soft_limit_tree_from_page(page);
+	if (!mctz)
+		return;
 	/*
 	 * Necessary to update all ancestors when hierarchy is used.
 	 * because their event counter is not touched.
@@ -502,7 +504,8 @@ static void mem_cgroup_remove_from_trees
 	for_each_node(nid) {
 		mz = mem_cgroup_nodeinfo(memcg, nid);
 		mctz = soft_limit_tree_node(nid);
-		mem_cgroup_remove_exceeded(mz, mctz);
+		if (mctz)
+			mem_cgroup_remove_exceeded(mz, mctz);
 	}
 }
 
@@ -2557,7 +2560,7 @@ unsigned long mem_cgroup_soft_limit_recl
 	 * is empty. Do it lockless to prevent lock bouncing. Races
 	 * are acceptable as soft limit is best effort anyway.
 	 */
-	if (RB_EMPTY_ROOT(&mctz->rb_root))
+	if (!mctz || RB_EMPTY_ROOT(&mctz->rb_root))
 		return 0;
 
 	/*
_

Patches currently in -mm which might be from ldufour@linux.vnet.ibm.com are

mm-cgroup-avoid-panic-when-init-with-low-memory.patch