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

[Bruce Ashfield]

On 2018-07-23 10:07 PM, He Zhe wrote:
> 
> 
> 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.

Rather than me guessing. Which versions are you looking at ? I've got
active -stable updates for many of the linux-yocto trees, so any number
could be impacted.

Bruce

> 
> 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();
>>>        }
>>>    }
>>>   
>>
>>
>