On 07/22/2013 05:22 PM, Lai Jiangshan wrote:
> On 07/19/2013 04:57 PM, Srivatsa S. Bhat wrote:
>> On 07/19/2013 07:17 AM, Lai Jiangshan wrote:
>>> On 07/19/2013 04:23 AM, Srivatsa S. Bhat wrote:
>>>>
>>>> ---
>>>>
>>>> kernel/workqueue.c | 6 ++++++
>>>> 1 file changed, 6 insertions(+)
>>>>
>>>>
>>>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>>>> index f02c4a4..07d9a67 100644
>>>> --- a/kernel/workqueue.c
>>>> +++ b/kernel/workqueue.c
>>>> @@ -4754,7 +4754,13 @@ long work_on_cpu(int cpu, long (*fn)(void *), void
>>>> *arg)
>>>> {
>>>> struct work_for_cpu wfc = { .fn = fn, .arg = arg };
>>>>
>>>> +#ifdef CONFIG_LOCKDEP
>>>> + static struct lock_class_key __key;
>>>
>>> Sorry, this "static" should be removed.
>>>
>>
>> That didn't help either :-( Because it makes lockdep unhappy,
>> since the key isn't persistent.
>>
>> This is the patch I used:
>>
>> ---
>>
>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>> index f02c4a4..7967e3b 100644
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -4754,7 +4754,13 @@ long work_on_cpu(int cpu, long (*fn)(void *), void
>> *arg)
>> {
>> struct work_for_cpu wfc = { .fn = fn, .arg = arg };
>>
>> +#ifdef CONFIG_LOCKDEP
>> + struct lock_class_key __key;
>> + INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
>> + lockdep_init_map(&wfc.work.lockdep_map, "&wfc.work", &__key, 0);
>> +#else
>> INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
>> +#endif
>> schedule_work_on(cpu, &wfc.work);
>> flush_work(&wfc.work);
>> return wfc.ret;
>>
>>
>> And here are the new warnings:
>>
>>
>> Block layer SCSI generic (bsg) driver version 0.4 loaded (major 252)
>> io scheduler noop registered
>> io scheduler deadline registered
>> io scheduler cfq registered (default)
>> BUG: key ffff881039557b98 not in .data!
>> ------------[ cut here ]------------
>> WARNING: CPU: 8 PID: 1 at kernel/lockdep.c:2987
>> lockdep_init_map+0x168/0x170()
>
> Sorry again.
>
> From 0096b9dac2282ec03d59a3f665b92977381a18ad Mon Sep 17 00:00:00 2001
> From: Lai Jiangshan <la...@cn.fujitsu.com>
> Date: Mon, 22 Jul 2013 19:08:51 +0800
> Subject: [PATCH] [PATCH] workqueue: allow the function of work_on_cpu() can
> call work_on_cpu()
>
> If the @fn call work_on_cpu() again, the lockdep will complain:
>
>> [ INFO: possible recursive locking detected ]
>> 3.11.0-rc1-lockdep-fix-a #6 Not tainted
>> ---------------------------------------------
>> kworker/0:1/142 is trying to acquire lock:
>> ((&wfc.work)){+.+.+.}, at: [<ffffffff81077100>] flush_work+0x0/0xb0
>>
>> but task is already holding lock:
>> ((&wfc.work)){+.+.+.}, at: [<ffffffff81075dd9>] process_one_work+0x169/0x610
>>
>> other info that might help us debug this:
>> Possible unsafe locking scenario:
>>
>> CPU0
>> ----
>> lock((&wfc.work));
>> lock((&wfc.work));
>>
>> *** DEADLOCK ***
>
> It is false-positive lockdep report. In this sutiation,
> the two "wfc"s of the two work_on_cpu() are different,
> they are both on stack. flush_work() can't be deadlock.
>
> To fix this, we need to avoid the lockdep checking in this case,
> But we don't want to change the flush_work(), so we use
> completion instead of flush_work() in the work_on_cpu().
>
> Reported-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
> Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
> ---
That worked, thanks a lot!
Tested-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
Regards,
Srivatsa S. Bhat
> kernel/workqueue.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index f02c4a4..b021a45 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4731,6 +4731,7 @@ struct work_for_cpu {
> long (*fn)(void *);
> void *arg;
> long ret;
> + struct completion done;
> };
>
> static void work_for_cpu_fn(struct work_struct *work)
> @@ -4738,6 +4739,7 @@ static void work_for_cpu_fn(struct work_struct *work)
> struct work_for_cpu *wfc = container_of(work, struct work_for_cpu,
> work);
>
> wfc->ret = wfc->fn(wfc->arg);
> + complete(&wfc->done);
> }
>
> /**
> @@ -4755,8 +4757,9 @@ long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
> struct work_for_cpu wfc = { .fn = fn, .arg = arg };
>
> INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
> + init_completion(&wfc.done);
> schedule_work_on(cpu, &wfc.work);
> - flush_work(&wfc.work);
> + wait_for_completion(&wfc.done);
> return wfc.ret;
> }
> EXPORT_SYMBOL_GPL(work_on_cpu);
>
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