linux-kernel - Re: BUG: sleeping function called from invalid context at kernel/stop

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Message-ID: <YAcNqqn3JRnZ1PmZ@hirez.programming.kicks-ass.net>
Date:   Tue, 19 Jan 2021 17:49:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: sleeping function called from invalid context at
 kernel/stop_machine.c:135

On Tue, Jan 19, 2021 at 11:45:02AM -0500, Waiman Long wrote:
> On 1/19/21 6:13 AM, Daniel Bristot de Oliveira wrote:
> > Hi Waiman,
> > 
> > Are you aware of this issue:
> > ----- %< -----
> > [   88.307857] BUG: sleeping function called from invalid context at kernel/stop_machine.c:135
> > [   88.308796] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 801, name: sh
> > [   88.309785] 6 locks held by sh/801:
> > [   88.310265]  #0: ffff9f008c575460 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x58/0xd0
> > [   88.310906]  #1: ffff9f008e9dd088 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write+0xa5/0x1c0
> > [   88.311672]  #2: ffff9f0092164a88 (kn->active#195){.+.+}-{0:0}, at: kernfs_fop_write+0xad/0x1c0
> > [   88.312456]  #3: ffffffffbac68310 (cpu_hotplug_lock){++++}-{0:0}, at: sched_partition_write+0x72/0x2f0
> > [   88.313280]  #4: ffffffffbae37090 (&cpuset_rwsem){++++}-{0:0}, at: sched_partition_write+0x7e/0x2f0
> > [   88.314095]  #5: ffffffffbad89140 (rcu_read_lock){....}-{1:3}, at: update_sibling_cpumasks+0x5/0x140
> > [   88.314806] Preemption disabled at:
> > [   88.314810] [<ffffffffb900454d>] preempt_schedule_thunk+0x16/0x18
> > [   88.315815] CPU: 1 PID: 801 Comm: sh Not tainted 5.10.0-rc5+ #10
> > [   88.316203] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
> > [   88.316714] Call Trace:
> > [   88.316875]  dump_stack+0x8b/0xb0
> > [   88.317087]  ___might_sleep.cold+0x102/0x116
> > [   88.317354]  stop_one_cpu+0x82/0xa0
> > [   88.317578]  ? set_cpus_allowed_ptr+0x10/0x10
> > [   88.317858]  __set_cpus_allowed_ptr+0x1e6/0x1f0
> > [   88.318144]  update_tasks_cpumask+0x25/0x50
> > [   88.318415]  update_cpumasks_hier+0x257/0x840
> > [   88.318687]  update_sibling_cpumasks+0x96/0x140
> > [   88.318968]  update_prstate+0x1a0/0x1f0
> > [   88.319210]  sched_partition_write+0x9f/0x2f0
> > [   88.319482]  kernfs_fop_write+0xdc/0x1c0
> > [   88.319730]  vfs_write+0xea/0x3b0
> > [   88.319943]  ksys_write+0x58/0xd0
> > [   88.320156]  do_syscall_64+0x33/0x40
> > [   88.320382]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > [   88.320692] RIP: 0033:0x7fbbd79be537
> > [   88.320915] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04
> > 		     25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3
> > 		     48 83 ec 28 48 89 54 24 18 48 89 74 24
> > [   88.322028] RSP: 002b:00007ffd44cc8398 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > [   88.322479] RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fbbd79be537
> > [   88.322910] RDX: 0000000000000005 RSI: 0000558ae69200a0 RDI: 0000000000000001
> > [   88.323342] RBP: 0000558ae69200a0 R08: 000000000000000a R09: 0000000000000004
> > [   88.323775] R10: 0000558ae6921ba0 R11: 0000000000000246 R12: 0000000000000005
> > [   88.325046] R13: 00007fbbd7a90500 R14: 0000000000000005 R15: 00007fbbd7a90700
> > ----- >% -----
> 
> I am not aware of that.
> 
> void ___might_sleep(const char *file, int line, int preempt_offset)
>   :
>         if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
>              !is_idle_task(current) && !current->non_block_count) ||
>             system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING
> ||
>             oops_in_progress)
>                 return;
> 
> I think the failing test was preempt_count_equals(preempt_offset).
> 
> static inline int preempt_count_equals(int preempt_offset)
> {
>         int nested = preempt_count() + rcu_preempt_depth();
> 
>         return (nested == preempt_offset);
> }
> 
> preempt_count() is 0 (in_atomic() == 0) and preempt_offset is 0, but
> rcu_preempt_depth() should be at least 1 as a rcu_read_lock was held. I
> don't think we should prevent sleeping if a rcu_read_lock is held. We need
> to look at the reason why rcu_preempt_depth() is included in this test.

You're not allowed to sleep with rcu_read_lock() held. With config
PREEMPT=y you're allowed to get preempted with rcu_read_lock() held, but
never to explicitly block.