linux-kernel - Re: [PATCH V2] ax25: Fix potential deadlock on &ax25_list

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Message-ID: <20231007151021.GC831234@kernel.org>
Date:   Sat, 7 Oct 2023 17:10:21 +0200
From:   Simon Horman <horms@...nel.org>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     jreuter@...na.de, ralf@...ux-mips.org, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        linux-hams@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] ax25: Fix potential deadlock on &ax25_list_lock

On Thu, Oct 05, 2023 at 07:23:49AM +0000, Chengfeng Ye wrote:
> Timer interrupt ax25_ds_timeout() could introduce double locks on
> &ax25_list_lock.
> 
> ax25_ioctl()
> --> ax25_ctl_ioctl()
> --> ax25_dama_off()
> --> ax25_dev_dama_off()
> --> ax25_check_dama_slave()
> --> spin_lock(&ax25_list_lock)
> <timer interrupt>
>    --> ax25_ds_timeout()
>    --> spin_lock(&ax25_list_lock)
> 
> This flaw was found by an experimental static analysis tool I am
> developing for irq-related deadlock.
> 
> To prevent the potential deadlock, the patch use spin_lock_bh()
> on &ax25_list_lock inside ax25_check_dama_slave().
> 
> Fixes: c19c4b9c9acb ("[AX.25]: Optimize AX.25 socket list lock")
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>

Hi Chengfeng Ye,

Are there other functions that spin_lock(&ax25_list_lock)
that also need to use spin_lock_bh()?

...