[linux-yocto] [PATCH] Revert mm/vmstat.c: fix vmstat_update() preemption BUG

[He Zhe]

On 2018年07月24日 03:21, Bruce Ashfield wrote:
> Which version/branches is this for ?
>

This is for linux-yocto rt branches. linux-yocto-4.12 does not need this
fix, since the commit, see below, causing the issue have not been included.

git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git

commit 08e9dbd5184e4e059adf1cc77b5dc08eca314a77
Author:     Steven J. Hill <steven.hill at cavium.com>
AuthorDate: Wed Mar 28 16:01:09 2018 -0700
Commit:     Greg Kroah-Hartman <gregkh at linuxfoundation.org>
CommitDate: Wed May 30 07:52:21 2018 +0200

    mm/vmstat.c: fix vmstat_update() preemption BUG


Thanks,
Zhe

> Given the author, I'm assuming it is for the -rt branches and also
> for 4.12 .. but I'd like a confirmation of that.
>
> Bruce
>
> On 2018-07-20 4:13 AM, zhe.he at windriver.com wrote:
>> From: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
>>
>> commit 97731753d44d5efcb95b994dc952c0e8195b3e96 upstream
>>
>> This patch reverts commit c7f26ccfb2c3 ("mm/vmstat.c: fix
>> vmstat_update() preemption BUG").
>> Steven saw a "using smp_processor_id() in preemptible" message and
>> added a preempt_disable() section around it to keep it quiet. This is
>> not the right thing to do it does not fix the real problem.
>>
>> vmstat_update() is invoked by a kworker on a specific CPU. This worker
>> it bound to this CPU. The name of the worker was "kworker/1:1" so it
>> should have been a worker which was bound to CPU1. A worker which can
>> run on any CPU would have a `u' before the first digit.
>>
>> smp_processor_id() can be used in a preempt-enabled region as long as
>> the task is bound to a single CPU which is the case here. If it could
>> run on an arbitrary CPU then this is the problem we have an should seek
>> to resolve.
>> Not only this smp_processor_id() must not be migrated to another CPU but
>> also refresh_cpu_vm_stats() which might access wrong per-CPU variables.
>> Not to mention that other code relies on the fact that such a worker
>> runs on one specific CPU only.
>>
>> Therefore I revert that commit and we should look instead what broke the
>> affinity mask of the kworker.
>>
>> Cc: Steven J. Hill <steven.hill at cavium.com>
>> Cc: Tejun Heo <htejun at gmail.com>
>> Cc: Andrew Morton <akpm at linux-foundation.org>
>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
>> Signed-off-by: Steven Rostedt (VMware) <rostedt at goodmis.org>
>>
>> Backport this to fix following serious crash for preempt-rt kernel
>>
>> BUG: scheduling while atomic: kworker/3:1/91/0x00000002
>> Preemption disabled at:
>> [<ffffffff8437c37d>] vmstat_update+0x2d/0xb0
>> CPU: 3 PID: 91 Comm: kworker/3:1 Not tainted 4.14.48-rt29-yocto-preempt-rt #1
>> Hardware name: Intel Corporation Broadwell Client platform/Basking Ridge, BIOS BDW-E2R1.86C.0118.R01.1503110618 03/11/2015
>> Workqueue: mm_percpu_wq vmstat_update
>> Call Trace:
>>   dump_stack+0x4f/0x6b
>>   ? vmstat_update+0x2d/0xb0
>>   __schedule_bug.cold.24+0x7d/0x9a
>>   __schedule+0x45a/0x6c0
>>   ? task_blocks_on_rt_mutex+0x173/0x300
>>   schedule+0x3d/0xd0
>>   rt_spin_lock_slowlock_locked+0x118/0x2a0
>>   rt_spin_lock_slowlock+0x48/0x60
>>   rt_spin_lock+0x3f/0x50
>>   queue_delayed_work_on+0x63/0x100
>>   vmstat_update+0x6e/0xb0
>>   process_one_work+0x1c3/0x430
>>   worker_thread+0x32/0x440
>>   kthread+0x127/0x140
>>   ? process_one_work+0x430/0x430
>>   ? kthread_create_on_node+0x40/0x40
>>   ret_from_fork+0x35/0x40
>>
>> Signed-off-by: He Zhe <zhe.he at windriver.com>
>> ---
>>   mm/vmstat.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index 84fd6eb..0d17b8f 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -1782,11 +1782,9 @@ static void vmstat_update(struct work_struct *w)
>>            * to occur in the future. Keep on running the
>>            * update worker thread.
>>            */
>> -        preempt_disable();
>>           queue_delayed_work_on(smp_processor_id(), mm_percpu_wq,
>>                   this_cpu_ptr(&vmstat_work),
>>                   round_jiffies_relative(sysctl_stat_interval));
>> -        preempt_enable();
>>       }
>>   }
>>  
>
>