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Date:   Sun, 29 Jan 2017 13:44:46 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     syzkaller <syzkaller@...glegroups.com>
Subject: mm: deadlock between get_online_cpus/pcpu_alloc

Hello,

I've got the following deadlock report while running syzkaller fuzzer
on f37208bc3c9c2f811460ef264909dfbc7f605a60:

[ INFO: possible circular locking dependency detected ]
4.10.0-rc5-next-20170125 #1 Not tainted
-------------------------------------------------------
syz-executor3/14255 is trying to acquire lock:
 (cpu_hotplug.dep_map){++++++}, at: [<ffffffff814271c7>]
get_online_cpus+0x37/0x90 kernel/cpu.c:239

but task is already holding lock:
 (pcpu_alloc_mutex){+.+.+.}, at: [<ffffffff81937fee>]
pcpu_alloc+0xbfe/0x1290 mm/percpu.c:897

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (pcpu_alloc_mutex){+.+.+.}:

[<ffffffff8157a169>] validate_chain kernel/locking/lockdep.c:2265 [inline]
[<ffffffff8157a169>] __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
[<ffffffff8157c2f1>] lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
[<ffffffff8447fb62>] __mutex_lock_common kernel/locking/mutex.c:757 [inline]
[<ffffffff8447fb62>] __mutex_lock+0x382/0x25c0 kernel/locking/mutex.c:894
[<ffffffff84481db6>] mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:909
[<ffffffff81937fee>] pcpu_alloc+0xbfe/0x1290 mm/percpu.c:897
[<ffffffff819386d4>] __alloc_percpu+0x24/0x30 mm/percpu.c:1076
[<ffffffff81684963>] smpcfd_prepare_cpu+0x73/0xd0 kernel/smp.c:47
[<ffffffff81428296>] cpuhp_invoke_callback+0x256/0x1480 kernel/cpu.c:136
[<ffffffff81429a11>] cpuhp_up_callbacks+0x81/0x2a0 kernel/cpu.c:425
[<ffffffff8142bd53>] _cpu_up+0x1e3/0x2a0 kernel/cpu.c:940
[<ffffffff8142be83>] do_cpu_up+0x73/0xa0 kernel/cpu.c:970
[<ffffffff8142bec8>] cpu_up+0x18/0x20 kernel/cpu.c:978
[<ffffffff8570eec9>] smp_init+0x148/0x160 kernel/smp.c:565
[<ffffffff856a2fef>] kernel_init_freeable+0x43e/0x695 init/main.c:1026
[<ffffffff8446ccf3>] kernel_init+0x13/0x180 init/main.c:955
[<ffffffff8448f0b1>] ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430

-> #1 (cpu_hotplug.lock){+.+.+.}:

[<ffffffff8157a169>] validate_chain kernel/locking/lockdep.c:2265 [inline]
[<ffffffff8157a169>] __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
[<ffffffff8157c2f1>] lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
[<ffffffff8447fb62>] __mutex_lock_common kernel/locking/mutex.c:757 [inline]
[<ffffffff8447fb62>] __mutex_lock+0x382/0x25c0 kernel/locking/mutex.c:894
[<ffffffff84481db6>] mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:909
[<ffffffff8142b9d6>] cpu_hotplug_begin+0x206/0x2e0 kernel/cpu.c:297
[<ffffffff8142bc3a>] _cpu_up+0xca/0x2a0 kernel/cpu.c:894
[<ffffffff8142be83>] do_cpu_up+0x73/0xa0 kernel/cpu.c:970
[<ffffffff8142bec8>] cpu_up+0x18/0x20 kernel/cpu.c:978
[<ffffffff8570eec9>] smp_init+0x148/0x160 kernel/smp.c:565
[<ffffffff856a2fef>] kernel_init_freeable+0x43e/0x695 init/main.c:1026
[<ffffffff8446ccf3>] kernel_init+0x13/0x180 init/main.c:955
[<ffffffff8448f0b1>] ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430

-> #0 (cpu_hotplug.dep_map){++++++}:

[<ffffffff81573ebf>] check_prev_add kernel/locking/lockdep.c:1828 [inline]
[<ffffffff81573ebf>] check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
[<ffffffff8157a169>] validate_chain kernel/locking/lockdep.c:2265 [inline]
[<ffffffff8157a169>] __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
[<ffffffff8157c2f1>] lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
[<ffffffff814271f2>] get_online_cpus+0x62/0x90 kernel/cpu.c:241
[<ffffffff818991ec>] drain_all_pages.part.98+0x8c/0x8f0 mm/page_alloc.c:2371
[<ffffffff818adac6>] drain_all_pages mm/page_alloc.c:2364 [inline]
[<ffffffff818adac6>] __alloc_pages_direct_reclaim mm/page_alloc.c:3435 [inline]
[<ffffffff818adac6>] __alloc_pages_slowpath+0x966/0x23d0 mm/page_alloc.c:3773
[<ffffffff818afe25>] __alloc_pages_nodemask+0x8f5/0xc60 mm/page_alloc.c:3975
[<ffffffff819348a1>] __alloc_pages include/linux/gfp.h:426 [inline]
[<ffffffff819348a1>] __alloc_pages_node include/linux/gfp.h:439 [inline]
[<ffffffff819348a1>] alloc_pages_node include/linux/gfp.h:453 [inline]
[<ffffffff819348a1>] pcpu_alloc_pages mm/percpu-vm.c:93 [inline]
[<ffffffff819348a1>] pcpu_populate_chunk+0x1e1/0x900 mm/percpu-vm.c:282
[<ffffffff81938205>] pcpu_alloc+0xe15/0x1290 mm/percpu.c:999
[<ffffffff819386a7>] __alloc_percpu_gfp+0x27/0x30 mm/percpu.c:1063
[<ffffffff81811913>] bpf_array_alloc_percpu kernel/bpf/arraymap.c:33 [inline]
[<ffffffff81811913>] array_map_alloc+0x543/0x700 kernel/bpf/arraymap.c:94
[<ffffffff817f53cd>] find_and_alloc_map kernel/bpf/syscall.c:37 [inline]
[<ffffffff817f53cd>] map_create kernel/bpf/syscall.c:228 [inline]
[<ffffffff817f53cd>] SYSC_bpf kernel/bpf/syscall.c:1040 [inline]
[<ffffffff817f53cd>] SyS_bpf+0x108d/0x27c0 kernel/bpf/syscall.c:997
[<ffffffff8448ee41>] entry_SYSCALL_64_fastpath+0x1f/0xc2

other info that might help us debug this:

Chain exists of:
  cpu_hotplug.dep_map --> cpu_hotplug.lock --> pcpu_alloc_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(pcpu_alloc_mutex);
                               lock(cpu_hotplug.lock);
                               lock(pcpu_alloc_mutex);
  lock(cpu_hotplug.dep_map);

 *** DEADLOCK ***

1 lock held by syz-executor3/14255:
 #0:  (pcpu_alloc_mutex){+.+.+.}, at: [<ffffffff81937fee>]
pcpu_alloc+0xbfe/0x1290 mm/percpu.c:897

stack backtrace:
CPU: 1 PID: 14255 Comm: syz-executor3 Not tainted 4.10.0-rc5-next-20170125 #1
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1202
 check_prev_add kernel/locking/lockdep.c:1828 [inline]
 check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
 validate_chain kernel/locking/lockdep.c:2265 [inline]
 __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
 lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
 get_online_cpus+0x62/0x90 kernel/cpu.c:241
 drain_all_pages.part.98+0x8c/0x8f0 mm/page_alloc.c:2371
 drain_all_pages mm/page_alloc.c:2364 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:3435 [inline]
 __alloc_pages_slowpath+0x966/0x23d0 mm/page_alloc.c:3773
 __alloc_pages_nodemask+0x8f5/0xc60 mm/page_alloc.c:3975
 __alloc_pages include/linux/gfp.h:426 [inline]
 __alloc_pages_node include/linux/gfp.h:439 [inline]
 alloc_pages_node include/linux/gfp.h:453 [inline]
 pcpu_alloc_pages mm/percpu-vm.c:93 [inline]
 pcpu_populate_chunk+0x1e1/0x900 mm/percpu-vm.c:282
 pcpu_alloc+0xe15/0x1290 mm/percpu.c:999
 __alloc_percpu_gfp+0x27/0x30 mm/percpu.c:1063
 bpf_array_alloc_percpu kernel/bpf/arraymap.c:33 [inline]
 array_map_alloc+0x543/0x700 kernel/bpf/arraymap.c:94
 find_and_alloc_map kernel/bpf/syscall.c:37 [inline]
 map_create kernel/bpf/syscall.c:228 [inline]
 SYSC_bpf kernel/bpf/syscall.c:1040 [inline]
 SyS_bpf+0x108d/0x27c0 kernel/bpf/syscall.c:997
 entry_SYSCALL_64_fastpath+0x1f/0xc2

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