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Subject: Re: use mutex instead of semaphore in RocketPort driver
From: Arjan van de Ven <arjan@infradead.org>
To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc: matthias.kaehlcke@gmail.com
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References: <200705081903.l48J3lr1012622@hera.kernel.org>
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Organization: Intel International BV
Date: Tue, 22 May 2007 09:59:01 -0700
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>  
> -	down_interruptible(&info->write_sem);
> +	mutex_lock_interruptible(&info->write_mtx);
>  
>  #ifdef ROCKET_DEBUG_WRITE
>  	printk(KERN_INFO "rp_write %d chars...", count);
> @@ -1773,7 +1776,7 @@ end:
>  		wake_up_interruptible(&tty->poll_wait);
>  #endif
>  	}
> -	up(&info->write_sem);
> +	mutex_unlock(&info->write_mtx);
>  	return retval

this code is very very buggy.

mutex_lock_interruptible() may not get the mutex in case a signal
happens... and yet you unlox the mutex unconditionally!!!