linux-kernel - RE: [PATCH] drivers: char: tlclk.c: Avoid data race between init and interrupt handler

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Date:   Fri, 17 Apr 2020 15:51:08 +0000
From:   "Gross, Mark" <mark.gross@...el.com>
To:     "madhuparnabhowmik10@...il.com" <madhuparnabhowmik10@...il.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "andrianov@...ras.ru" <andrianov@...ras.ru>,
        "ldv-project@...uxtesting.org" <ldv-project@...uxtesting.org>
Subject: RE: [PATCH] drivers: char: tlclk.c: Avoid data race between init and
 interrupt handler

Looks reasonable to me.
+1
Ack
--mark

> -----Original Message-----
> From: madhuparnabhowmik10@...il.com <madhuparnabhowmik10@...il.com>
> Sent: Friday, April 17, 2020 8:35 AM
> To: Gross, Mark <mark.gross@...el.com>; arnd@...db.de;
> gregkh@...uxfoundation.org
> Cc: linux-kernel@...r.kernel.org; andrianov@...ras.ru; ldv-
> project@...uxtesting.org; Madhuparna Bhowmik
> <madhuparnabhowmik10@...il.com>
> Subject: [PATCH] drivers: char: tlclk.c: Avoid data race between init and interrupt
> handler
> 
> From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> 
> After registering character device the file operation callbacks can be called. The
> open callback registers interrupt handler.
> Therefore interrupt handler can execute in parallel with rest of the init function. To
> avoid such data race initialize telclk_interrupt variable and struct alarm_events
> before registering character device.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> ---
>  drivers/char/tlclk.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/char/tlclk.c b/drivers/char/tlclk.c index
> 6d81bb3bb503..896a3550fba9 100644
> --- a/drivers/char/tlclk.c
> +++ b/drivers/char/tlclk.c
> @@ -777,17 +777,21 @@ static int __init tlclk_init(void)  {
>  	int ret;
> 
> +	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
> +
> +	alarm_events = kzalloc( sizeof(struct tlclk_alarms), GFP_KERNEL);
> +	if (!alarm_events) {
> +		ret = -ENOMEM;
> +		goto out1;
> +	}
> +
>  	ret = register_chrdev(tlclk_major, "telco_clock", &tlclk_fops);
>  	if (ret < 0) {
>  		printk(KERN_ERR "tlclk: can't get major %d.\n", tlclk_major);
> +		kfree(alarm_events);
>  		return ret;
>  	}
>  	tlclk_major = ret;
> -	alarm_events = kzalloc( sizeof(struct tlclk_alarms), GFP_KERNEL);
> -	if (!alarm_events) {
> -		ret = -ENOMEM;
> -		goto out1;
> -	}
> 
>  	/* Read telecom clock IRQ number (Set by BIOS) */
>  	if (!request_region(TLCLK_BASE, 8, "telco_clock")) { @@ -796,7 +800,6
> @@ static int __init tlclk_init(void)
>  		ret = -EBUSY;
>  		goto out2;
>  	}
> -	telclk_interrupt = (inb(TLCLK_REG7) & 0x0f);
> 
>  	if (0x0F == telclk_interrupt ) { /* not MCPBL0010 ? */
>  		printk(KERN_ERR "telclk_interrupt = 0x%x non-mcpbl0010 hw.\n",
> @@ -837,8 +840,8 @@ static int __init tlclk_init(void)
>  	release_region(TLCLK_BASE, 8);
>  out2:
>  	kfree(alarm_events);
> -out1:
>  	unregister_chrdev(tlclk_major, "telco_clock");
> +out1:
>  	return ret;
>  }
> 
> --
> 2.17.1