linux-kernel - Re: [2.4 patch] Port of adutux driver from 2.6 kernel to 2.4.

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Date:	Sun, 4 Nov 2007 15:05:52 +0100
From:	Willy Tarreau <w@....eu>
To:	vitalivanov@...il.com
Cc:	Pete Zaitcev <zaitcev@...hat.com>,
	linux-usb-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [2.4 patch] Port of adutux driver from 2.6 kernel to 2.4.

On Mon, Oct 22, 2007 at 08:45:39PM -0700, Pete Zaitcev wrote:
> On Fri, 19 Oct 2007 20:40:35 +0300, Vitaliy Ivanov <vitalivanov@...il.com> wrote:
> 
> Hi, Vitaly, I added you on cc: for the 2.6 cleanup. Please double-check
> what I'm doing there and use it for your 2.4 version. I hope my intentions
> get clearer with an example. Now, about the specific question:
> 
> > Static lock minor_table_mutex is used for minor table structure.
> > And dev->sem for dev manipulations and that's why for open_count.
> > If you will simply browse /drivers/usb dir for 2.4 you will see that
> > such approach is widely used there.
> > What's not right?
> 
> The fundamental reason why you cannot lock a free-able structure with
> an in-structure lock is this. Imagine thread A locks in order to process
> a disconnect. Thread B wants to open and waits for the lock. Notice that
> the struct is not open, so thread A frees it. At this point, thread B
> is using a freed memory.
> 
> The solution is to lock the instance struct dev with dev->mtx, except
> for the open count, which is locked by a static lock (I'm ignoring
> interrupts here, which cannot use mutexes).
> 
> I'm sorry to say, you're quite right: a number of drivers in 2.4 got
> it wrong, and some (like adutux) carried it through 2.6.23.

Vitaly,

I'm planning on issuing a new 2.4.36 prerelease soon. Have you made any
progress on your code after Pete's recommendations ?

Thanks,
Willy

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