[BUG -next] "random: make /dev/urandom scalable for silly userspace programs" causes crash

Heiko Carstens
2016-07-27T07:14:20Z

Hi Ted,

it looks like your patch "random: make /dev/urandom scalable for silly
userspace programs" within linux-next seems to be a bit broken:

It causes this allocation failure and subsequent crash on s390 with fake
NUMA enabled:

[ 0.533195] SLUB: Unable to allocate memory on node 1, gfp=0x24008c0(GFP_KERNEL|__GFP_NOFAIL)
[ 0.533198] cache: kmalloc-192, object size: 192, buffer size: 528, defaul order: 3, min order: 0
[ 0.533202] node 0: slabs: 2, objs: 124, free: 17
[ 0.533208] Unable to handle kernel pointer dereference in virtual kernel address space
[ 0.533211] Failing address: 0000000000000000 TEID: 0000000000000483
...
[ 0.533276] Krnl PSW : 0704e00180000000 00000000001a853e (lockdep_init_map+0x1e/0x220)
[ 0.533281] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000a23400 00000000370c8008 0000000000000060 0000000000bedc90
[ 0.533285] 0000000002070800 0000000000000000 0000000000000001 0000000000000000
[ 0.533287] 000000003743d3f8 000000003743d408 0000000002070800 0000000000bedc90
[ 0.533289] 0000000000000048 00000000009c2030 00000000370cfd00 00000000370cfcc0
[ 0.533295] Krnl Code: 00000000001a852e: a7840001 brc 8,1a8530
00000000001a8532: e3f0ffc0ff71 lay %r15,-64(%r15)
#00000000001a8538: e3e0f0980024 stg %r14,152(%r15)
>00000000001a853e: e54820080000 mvghi 8(%r2),0
00000000001a8544: e54820100000 mvghi 16(%r2),0
00000000001a854a: 58100370 l %r1,880
00000000001a854e: 50102020 st %r1,32(%r2)
00000000001a8552: b90400c2 lgr %r12,%r2
[ 0.533313] Call Trace:
[ 0.533315] ([<0000000000000001>] 0x1)
[ 0.533318] ([<00000000001b4220>] __raw_spin_lock_init+0x50/0x80)
[ 0.533320] ([<0000000000759e7a>] rand_initialize+0xc2/0xf0)
[ 0.533322] ([<00000000001002cc>] do_one_initcall+0xb4/0x140)
[ 0.533325] ([<0000000000ef2cc0>] kernel_init_freeable+0x140/0x2d8)
[ 0.533328] ([<00000000009b07ea>] kernel_init+0x2a/0x150)
[ 0.533330] ([<00000000009bd782>] kernel_thread_starter+0x6/0xc)
[ 0.533332] ([<00000000009bd77c>] kernel_thread_starter+0x0/0xc)

To me it looks rand_initialize is broken with CONFIG_NUMA:

static int rand_initialize(void)
{
#ifdef CONFIG_NUMA
int i;
int num_nodes = num_possible_nodes();
struct crng_state *crng;
struct crng_state **pool;
#endif

init_std_data(&input_pool);
init_std_data(&blocking_pool);
crng_initialize(&primary_crng);

#ifdef CONFIG_NUMA
pool = kmalloc(num_nodes * sizeof(void *),
GFP_KERNEL|__GFP_NOFAIL|__GFP_ZERO);
for (i=0; i < num_nodes; i++) {
crng = kmalloc_node(sizeof(struct crng_state),
GFP_KERNEL | __GFP_NOFAIL, i);
spin_lock_init(&crng->lock);
crng_initialize(crng);
pool[i] = crng;

}
mb();
crng_node_pool = pool;
#endif
return 0;
}
early_initcall(rand_initialize);

First the for loop should use for_each_node() to skip not possible nodes,
no?

However that wouldn't be enough, since in this case it crashed because node
1 is in the possible map, but it isn't online and doesn't have any memory,
which explains why the allocation fails and the subsequent crash when
calling spin_lock_init().

I think the proper fix would be to simply use for_each_online_node(); at
least that fixes the crash on s390.