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Subject: Re: [PATCH v2] async: Let kfree() out of the critical area of the
 lock
To:     Thomas Gleixner <tglx@linutronix.de>
CC:     Bart Van Assche <bvanassche@acm.org>, <dsterba@suse.cz>,
        <bhelgaas@google.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        <sakari.ailus@linux.intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        David Sterba <dsterba@suse.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "hushiyuan@huawei.com" <hushiyuan@huawei.com>,
        "linfeilong@huawei.com" <linfeilong@huawei.com>
References: <ae3b790d-9883-0ec0-425d-5ac9b32c2d0f@huawei.com>
 <9bfecf17-3c1b-414e-b271-4fd2d884faa3@huawei.com>
 <alpine.DEB.2.21.1911151931420.28787@nanos.tec.linutronix.de>
From:   Yunfeng Ye <yeyunfeng@huawei.com>
Message-ID: <d44b91fb-95d9-fadb-535f-898cca512bf4@huawei.com>
Date:   Tue, 19 Nov 2019 11:01:15 +0800
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On 2019/11/16 2:32, Thomas Gleixner wrote:
> 
> 
> On Fri, 11 Oct 2019, Yunfeng Ye wrote:
> 
>> The async_lock is big global lock, and kfree() is not always cheap, it
>> will increase lock contention. it's better let kfree() outside the lock
>> to keep the critical area as short as possible.
>>
>> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
>> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
>> ---
>> v1 -> v2:
>>  - update the description
>>  - add "Reviewed-by"
>>
>>  kernel/async.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/async.c b/kernel/async.c
>> index 4f9c1d6..1de270d 100644
>> --- a/kernel/async.c
>> +++ b/kernel/async.c
>> @@ -135,12 +135,12 @@ static void async_run_entry_fn(struct work_struct *work)
>>  	list_del_init(&entry->domain_list);
>>  	list_del_init(&entry->global_list);
>>
>> -	/* 3) free the entry */
>> -	kfree(entry);
>>  	atomic_dec(&entry_count);
>> -
>>  	spin_unlock_irqrestore(&async_lock, flags);
>>
>> +	/* 3) free the entry */
>> +	kfree(entry);
>> +
>>  	/* 4) wake up any waiters */
>>  	wake_up(&async_done);
> 
> The wakeup should happen before the kfree() for the very same reasons.
> 
ok, I will modify as your suggest, thanks.

> Thanks,
> 
> 	tglx
> 
> .
>