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SubjectRe: [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()
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On 15.03.2018 01:22, Andrew Morton wrote:
> On Wed, 14 Mar 2018 15:09:09 -0700 Tejun Heo <tj@kernel.org> wrote:
>
>> Hello, Andrew.
>>
>> On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote:
>>> It would benefit from a comment explaining why we're doing this (it's
>>> for the oom-killer).
>>
>> Will add.
>>
>>> My memory is weak and our documentation is awful. What does
>>> mutex_lock_killable() actually do and how does it differ from
>>> mutex_lock_interruptible()? Userspace tasks can run pcpu_alloc() and I
>>
>> IIRC, killable listens only to SIGKILL.
>>
>>> wonder if there's any way in which a userspace-delivered signal can
>>> disrupt another userspace task's memory allocation attempt?
>>
>> Hmm... maybe. Just honoring SIGKILL *should* be fine but the alloc
>> failure paths might be broken, so there are some risks. Given that
>> the cases where userspace tasks end up allocation percpu memory is
>> pretty limited and/or priviledged (like mount, bpf), I don't think the
>> risks are high tho.
>
> hm. spose so. Maybe. Are there other ways? I assume the time is
> being spent in pcpu_create_chunk()? We could drop the mutex while
> running that stuff and take the appropriate did-we-race-with-someone
> testing after retaking it. Or similar.

The balance work spends its time in pcpu_populate_chunk(). There are
two stacks of this problem:

[ 106.313267] kworker/2:2 D13832 936 2 0x80000000
[ 106.313740] Workqueue: events pcpu_balance_workfn
[ 106.314109] Call Trace:
[ 106.314293] ? __schedule+0x267/0x750
[ 106.314570] schedule+0x2d/0x90
[ 106.314803] schedule_timeout+0x17f/0x390
[ 106.315106] ? __next_timer_interrupt+0xc0/0xc0
[ 106.315429] __alloc_pages_slowpath+0xb73/0xd90
[ 106.315792] __alloc_pages_nodemask+0x16a/0x210
[ 106.316148] pcpu_populate_chunk+0xce/0x300
[ 106.316479] pcpu_balance_workfn+0x3f3/0x580
[ 106.316853] ? _raw_spin_unlock_irq+0xe/0x30
[ 106.317227] ? finish_task_switch+0x8d/0x250
[ 106.317632] process_one_work+0x1b7/0x410
[ 106.317970] worker_thread+0x26/0x3d0
[ 106.318304] ? process_one_work+0x410/0x410
[ 106.318649] kthread+0x10e/0x130
[ 106.318916] ? __kthread_create_worker+0x120/0x120
[ 106.319360] ret_from_fork+0x35/0x40

[ 106.453375] a.out D13400 3670 1 0x00100004
[ 106.453880] Call Trace:
[ 106.454114] ? __schedule+0x267/0x750
[ 106.454427] schedule+0x2d/0x90
[ 106.454829] schedule_preempt_disabled+0xf/0x20
[ 106.455422] __mutex_lock.isra.2+0x181/0x4d0
[ 106.455988] ? pcpu_alloc+0x3c4/0x670
[ 106.456465] pcpu_alloc+0x3c4/0x670
[ 106.456973] ? preempt_count_add+0x63/0x90
[ 106.457401] ? __local_bh_enable_ip+0x2e/0x60
[ 106.457882] ipv6_add_dev+0x121/0x490
[ 106.458330] addrconf_notify+0x27b/0x9a0
[ 106.458823] ? inetdev_init+0xd7/0x150
[ 106.459270] ? inetdev_event+0x339/0x4b0
[ 106.459738] ? preempt_count_add+0x63/0x90
[ 106.460243] ? _raw_spin_lock_irq+0xf/0x30
[ 106.460747] ? notifier_call_chain+0x42/0x60
[ 106.461271] notifier_call_chain+0x42/0x60
[ 106.461819] register_netdevice+0x415/0x530
[ 106.462364] register_netdev+0x11/0x20
[ 106.462849] loopback_net_init+0x43/0x90
[ 106.463216] ops_init+0x3b/0x100
[ 106.463516] setup_net+0x7d/0x150
[ 106.463831] copy_net_ns+0x14b/0x180
[ 106.464134] create_new_namespaces+0x117/0x1b0
[ 106.464481] unshare_nsproxy_namespaces+0x5b/0x90
[ 106.464864] SyS_unshare+0x1b0/0x300

[ 106.536845] Kernel panic - not syncing: Out of memory and no killable processes...

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