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Message-ID: <4fa62e4f-9768-4434-8f7b-24aa3b2a3490@xs4all.nl>
Date: Wed, 21 Feb 2024 15:38:47 +0100
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Subject: Re: [PATCH] media/cec/core: fix task hung in cec_claim_log_addrs
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To: Edward Adam Davis <eadavis@qq.com>,
 syzbot+116b65a23bc791ae49a6@syzkaller.appspotmail.com
Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
 mchehab@kernel.org, syzkaller-bugs@googlegroups.com
References: <0000000000006d96200611de3986@google.com>
 <tencent_941B48254CBA00BB4933069E391B6E4B5408@qq.com>
From: Hans Verkuil <hverkuil-cisco@xs4all.nl>
In-Reply-To: <tencent_941B48254CBA00BB4933069E391B6E4B5408@qq.com>
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On 21/02/2024 15:20, Edward Adam Davis wrote:
> After unlocking adap->lock in cec_claim_log_addrs(), cec_claim_log_addrs() may
> re-enter, causing this issue to occur.

But if it is called again, then it should hit this at the start of the function:

        if (WARN_ON(adap->is_configuring || adap->is_configured))
                return;

I'm still not sure what causes the KASAN hung task since I cannot seem to reproduce
it, and because it is hard for me to find enough time to dig into this.

Regards,

	Hans

> 
> In the thread function cec_config_thread_func() adap->lock is also used, so there
> is no need to unlock adap->lock in cec_claim_log_addrs(), and then use adap->lock
> in cec_config_thread_func() to protect.
> 
> Reported-and-tested-by: syzbot+116b65a23bc791ae49a6@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/media/cec/core/cec-adap.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/media/cec/core/cec-adap.c b/drivers/media/cec/core/cec-adap.c
> index 5741adf09a2e..21b3ff504524 100644
> --- a/drivers/media/cec/core/cec-adap.c
> +++ b/drivers/media/cec/core/cec-adap.c
> @@ -1436,7 +1436,6 @@ static int cec_config_thread_func(void *arg)
>  	int err;
>  	int i, j;
>  
> -	mutex_lock(&adap->lock);
>  	dprintk(1, "physical address: %x.%x.%x.%x, claim %d logical addresses\n",
>  		cec_phys_addr_exp(adap->phys_addr), las->num_log_addrs);
>  	las->log_addr_mask = 0;
> @@ -1565,7 +1564,6 @@ static int cec_config_thread_func(void *arg)
>  	}
>  	adap->kthread_config = NULL;
>  	complete(&adap->config_completion);
> -	mutex_unlock(&adap->lock);
>  	call_void_op(adap, configured);
>  	return 0;
>  
> @@ -1577,7 +1575,6 @@ static int cec_config_thread_func(void *arg)
>  	adap->must_reconfigure = false;
>  	adap->kthread_config = NULL;
>  	complete(&adap->config_completion);
> -	mutex_unlock(&adap->lock);
>  	return 0;
>  }
>  
> @@ -1602,9 +1599,7 @@ static void cec_claim_log_addrs(struct cec_adapter *adap, bool block)
>  		adap->kthread_config = NULL;
>  		adap->is_configuring = false;
>  	} else if (block) {
> -		mutex_unlock(&adap->lock);
>  		wait_for_completion(&adap->config_completion);
> -		mutex_lock(&adap->lock);
>  	}
>  }
>