linux-kernel - Re: [PATCH 1/2] i2c: imx: use guard to take spinlock

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: <54d062af-40ff-47b7-baec-c7e883defea3@pengutronix.de>
Date: Tue, 22 Apr 2025 17:53:11 +0200
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Troy Mitchell <troymitchell988@...il.com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: imx@...ts.linux.dev, Andi Shyti <andi.shyti@...nel.org>,
 Fabio Estevam <festevam@...il.com>, Sascha Hauer <s.hauer@...gutronix.de>,
 linux-kernel@...r.kernel.org, Oleksij Rempel <o.rempel@...gutronix.de>,
 linux-i2c@...r.kernel.org, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Yongchao Jia <jyc0019@...il.com>, Shawn Guo <shawnguo@...nel.org>,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] i2c: imx: use guard to take spinlock

Hello Troy,

On 4/22/25 17:26, Troy Mitchell wrote:
> On 2025/4/22 23:12, Jonathan Cameron wrote:
>> On Mon, 21 Apr 2025 13:36:38 +0800

[snip]

>> In this path the patch changes the lock release to occur after
>> i2c_imx_master_isr(i2c_imx, status);
>>
>> That may well be safe; I have no idea!  You should talk about that
>> in the patch description if it is.
> You're correct that this change slightly alters the lock release timing.
> 
> However, both i2c_imx_slave_handle() and i2c_imx_master_isr() can safely be
> entered with the lock held — there's no requirement for the lock to be released
> before calling them.

Why would we want to hold a spinlock out of all things longer than
absolutely necessary?

> Using guard(spinlock_irqsave) simplifies the control flow by ensuring consistent
> and automatic unlock, which improves readability without affecting correctness.
> 
> I'll update the commit message to clarify this.

Sorry, I don't think that this simplification is worth potentially
increasing the time we spend with preemption disabled,
i2c_imx_master_isr() even has a loop inside.

Guards that don't increase critical section size however are fine by me.

Thanks,
Ahmad

> 
>>
>>> +
>>>  		return i2c_imx_master_isr(i2c_imx, status);
>>>  	}
>>> -	spin_unlock_irqrestore(&i2c_imx->slave_lock, flags);
>>>  
>>>  	return IRQ_NONE;
>>>  }
> 

-- 
Pengutronix e.K.                  |                             |
Steuerwalder Str. 21              | http://www.pengutronix.de/  |
31137 Hildesheim, Germany         | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686  | Fax:   +49-5121-206917-5555 |