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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.1911151931420.28787@nanos.tec.linutronix.de>
Date:   Fri, 15 Nov 2019 19:32:26 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Yunfeng Ye <yeyunfeng@...wei.com>
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>
Subject: Re: [PATCH v2] async: Let kfree() out of the critical area of the
 lock



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.

Thanks,

	tglx