linux-kernel - Re: [PATCH v2] async: Let kfree() out of the critical area of the lock

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Date:   Tue, 19 Nov 2019 11:01:15 +0800
From:   Yunfeng Ye <yeyunfeng@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Bart Van Assche <bvanassche@....org>, <dsterba@...e.cz>,
        <bhelgaas@...gle.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        <sakari.ailus@...ux.intel.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        David Sterba <dsterba@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hushiyuan@...wei.com" <hushiyuan@...wei.com>,
        "linfeilong@...wei.com" <linfeilong@...wei.com>
Subject: Re: [PATCH v2] async: Let kfree() out of the critical area of the
 lock



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@...wei.com>
>> Reviewed-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
>> Reviewed-by: Bart Van Assche <bvanassche@....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
> 
> .
>