BUG: unable to handle kernel NULL pointer dereference in shrink_slab

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 3ee15ba60e6b Add linux-next specific files for 20180712
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14365370400000
kernel config: https://syzkaller.appspot.com/x/.config?x=fe1c3df2c7c0c81
dashboard link: https://syzkaller.appspot.com/bug?extid=84c762f1af3fde51a761
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [ak...@linux-foundation.org arya...@virtuozzo.com
jba...@fb.com ktk...@virtuozzo.com linux-...@vger.kernel.org
linu...@kvack.org mho...@suse.com penguin...@I-love.SAKURA.ne.jp
s...@canb.auug.org.au shak...@google.com vdavyd...@gmail.com
wi...@infradead.org ying....@intel.com]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+84c762...@syzkaller.appspotmail.com

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 1b041a067 P4D 1b041a067 PUD 1caf57067 PMD 0
Oops: 0010 [#1] SMP KASAN
CPU: 1 PID: 26512 Comm: syz-executor7 Not tainted 4.18.0-rc4-next-20180712+
#5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff8801a957e9a0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffc90001e34000
RDX: 1ffff10039868e56 RSI: ffff8801a957ec20 RDI: ffff8801cc3472b0
RBP: ffff8801a957eb90 R08: ffff8801c99aa440 R09: ffffed003981c8c0
R10: ffffed003981c8c0 R11: ffff8801cc0e4607 R12: ffff8801a957ec20
R13: ffff8801cc3472b0 R14: ffff8801cc3472d8 R15: 0000000000000080
FS: 00007f12a8407700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000001b297f000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
shrink_slab_memcg mm/vmscan.c:598 [inline]
shrink_slab+0x861/0xa60 mm/vmscan.c:671
shrink_node+0x429/0x16a0 mm/vmscan.c:2735
shrink_zones mm/vmscan.c:2964 [inline]
do_try_to_free_pages+0x3e7/0x1290 mm/vmscan.c:3026
try_to_free_mem_cgroup_pages+0x49d/0xc90 mm/vmscan.c:3324
memory_high_write+0x283/0x310 mm/memcontrol.c:5611
cgroup_file_write+0x31f/0x840 kernel/cgroup/cgroup.c:3502
kernfs_fop_write+0x2ba/0x480 fs/kernfs/file.c:316
__vfs_write+0x117/0x9d0 fs/read_write.c:485
__kernel_write+0x10c/0x370 fs/read_write.c:506
write_pipe_buf+0x181/0x240 fs/splice.c:798
splice_from_pipe_feed fs/splice.c:503 [inline]
__splice_from_pipe+0x38e/0x7c0 fs/splice.c:627
splice_from_pipe+0x1ea/0x340 fs/splice.c:662
default_file_splice_write+0x3c/0x90 fs/splice.c:810
do_splice_from fs/splice.c:852 [inline]
direct_splice_actor+0x128/0x190 fs/splice.c:1019
splice_direct_to_actor+0x318/0x8f0 fs/splice.c:974
do_splice_direct+0x2d4/0x420 fs/splice.c:1062
do_sendfile+0x62a/0xe20 fs/read_write.c:1440
__do_sys_sendfile64 fs/read_write.c:1495 [inline]
__se_sys_sendfile64 fs/read_write.c:1487 [inline]
__x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1487
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455e29
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f12a8406c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f12a84076d4 RCX: 0000000000455e29
RDX: 0000000020000040 RSI: 0000000000000016 RDI: 0000000000000016
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c1113 R14: 00000000004d1540 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
(ftrace buffer empty)
CR2: 0000000000000000
---[ end trace 163e0fbe410a32c7 ]---
RIP: 0010: (null)
Code: Bad RIP value.
RSP: 0018:ffff8801a957e9a0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffc90001e34000
RDX: 1ffff10039868e56 RSI: ffff8801a957ec20 RDI: ffff8801cc3472b0
RBP: ffff8801a957eb90 R08: ffff8801c99aa440 R09: ffffed003981c8c0
R10: ffffed003981c8c0 R11: ffff8801cc0e4607 R12: ffff8801a957ec20
R13: ffff8801cc3472b0 R14: ffff8801cc3472d8 R15: 0000000000000080
FS: 00007f12a8407700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000001b297f000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[Dmitry Vyukov]

This stopped happening 4+ months ago, let's prevent potential new
future crashes from merging into this

#syz invalid

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