Re: [PATCH] tty reference count fix

[Jesper Juhl <jesper.juhl@gmail.com>]

On 2/13/06, Paul Fulghum <paulkf@microgate.com> wrote:
> Fix hole where tty structure can be released when reference
> count is non zero. Existing code can sleep without tty_sem
> protection between deciding to release the tty structure
> (setting local variables tty_closing and otty_closing)
> and setting TTY_CLOSING to prevent further opens.
> An open can occur during this interval causing release_dev()
> to free the tty structure while it is still referenced.
>
> This should fix bugzilla.kernel.org
> [Bug 6041] New: Unable to handle kernel paging request
>
> In Bug 6041, tty_open() oopes on accessing the tty structure
> it has successfully claimed. Bug was on SMP machine
> with the same tty being opened and closed by
> multiple processes, and DEBUG_PAGEALLOC enabled.
>
> Signed-off-by: Paul Fulghum <paulkf@microgate.com>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> Cc: Jesper Juhl <jesper.juhl@gmail.com>
>

I just applied the patch to 2.6.16-rc3 and booted the patched kernel.
Unfortunately I can't tell you if it fixes the bug since I never
successfully reproduced it, it just happened once out of the blue.
What I can tell you though is that the patched kernel seems to behave
just fine and doesn't seem to introduce any regressions on my system -
but my testing has been quite limited so far.

Not the best feedback, I know, but it's the best I can give you at the moment.


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Jesper Juhl <jesper.juhl@gmail.com>
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