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Subject[PATCH for 4.9 30/39] mm/cgroup: avoid panic when init with low memory
Date
From: Laurent Dufour <ldufour@linux.vnet.ibm.com>

[ Upstream commit bfc7228b9a9647e1c353e50b40297a2929801759 ]

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:

Unable to handle kernel paging request for data at address 0x00000000
Faulting instruction address: 0xc000000000302b88
Oops: Kernel access of bad area, sig: 11 [#1]
SMP NR_CPUS=2048 [ 0.082424] NUMA
pSeries
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.9.0-15-generic #16-Ubuntu
task: c00000021ed01600 task.stack: c00000010d108000
NIP: c000000000302b88 LR: c000000000270e04 CTR: c00000000016cfd0
REGS: c00000010d10b2c0 TRAP: 0300 Not tainted (4.9.0-15-generic)
MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE>[ 0.082770] CR: 28424422 XER: 00000000
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 mem_cgroup_soft_limit_reclaim+0xf8/0x4f0
LR do_try_to_free_pages+0x1b4/0x450
Call Trace:
do_try_to_free_pages+0x1b4/0x450
try_to_free_pages+0xf8/0x270
__alloc_pages_nodemask+0x7a8/0xff0
new_slab+0x104/0x8e0
___slab_alloc+0x620/0x700
__slab_alloc+0x34/0x60
kmem_cache_alloc_node_trace+0xdc/0x310
mem_cgroup_init+0x158/0x1c8
do_one_initcall+0x68/0x1d0
kernel_init_freeable+0x278/0x360
kernel_init+0x24/0x170
ret_from_kernel_thread+0x5c/0x74
Instruction dump:
eb81ffe0 eba1ffe8 ebc1fff0 ebe1fff8 4e800020 3d230001 e9499a42 3d220004
3929acd8 794a1f24 7d295214 eac90100 <e9360000> 2fa90000 419eff74 3b200000
---[ 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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
---
mm/memcontrol.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 47559cc0cdcc..2a800c4a39bd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -462,6 +462,8 @@ static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
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.
@@ -499,7 +501,8 @@ static void mem_cgroup_remove_from_trees(struct mem_cgroup *memcg)
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);
}
}

@@ -2565,7 +2568,7 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
* 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;

/*
--
2.11.0
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