linux-kernel - Re: [PATCH] use mutex instead of semaphore in RocketPort driver

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Date:	Tue, 24 Apr 2007 17:53:41 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Matthias Kaehlcke <matthias.kaehlcke@...il.com>,
	Oliver Neukum <oneukum@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] use mutex instead of semaphore in RocketPort driver

Matthias Kaehlcke wrote:
> El Tue, Apr 24, 2007 at 07:53:04PM +0200 Oliver Neukum ha dit:
> 
>> Am Dienstag, 24. April 2007 19:49 schrieb Matthias Kaehlcke:
>>> @@ -1706,7 +1706,7 @@ static int rp_write(struct tty_struct *tty,
>>>         if (count <= 0 || rocket_paranoia_check(info, "rp_write"))
>>>                 return 0;
>>>  
>>> -       down_interruptible(&info->write_sem);
>>> +       mutex_lock_interruptible(&info->write_mtx);
>> This is a bug. It is also present in the current code, but nevertheless
>> it is a bug. If you use an interruptible lock, you must be ready to deal
>> with interrupts, which are ignored by this code.
> 
> i fear i don't have the experience/knowledge to fix this bug, thanks
> for your remark. 
> 
> i'm a bit confused now about the interruptible locks, i thought using
> them means that the process will be waked up when receiving a
> signal. what role are playing interrupts when using interruptible locks?

You are correct, interrupts aren't involved. However if the wait is 
interrupted by a signal, mutex_lock_interruptible will return a nonzero 
return code which needs to be checked for (and likely -ERESTARTSYS or 
-EINTR returned), otherwise the code will blindly continue as though it 
has locked the mutex even though it has not.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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