linux-kernel - Re: [PATCH] hvc: ensure hvc_init is only ever called once in hvc

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Date:	Tue, 14 Jan 2014 13:13:33 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] hvc: ensure hvc_init is only ever called once in
 hvc_console.c

On Tue, Jan 14, 2014 at 04:03:37PM -0500, Paul Gortmaker wrote:
> Commit 3e6c6f630a5282df8f3393a59f10eb9c56536d23 ("Delay creation of
> khcvd thread") moved the call of hvc_init from being a device_initcall
> into hvc_alloc, and used a non-null hvc_driver as indication of whether
> hvc_init had already been called.
> 
> The problem with this is that hvc_driver is only assigned a value
> at the bottom of hvc_init, and so there is a window where multiple
> hvc_alloc calls can be in progress at the same time and hence try
> and call hvc_init multiple times.  Previously the use of device_init
> guaranteed that hvc_init was only called once.
> 
> This manifests itself as sporadic instances of two hvc_init calls
> racing each other, and with the loser of the race getting -EBUSY
> from tty_register_driver() and hence that virtual console fails:
> 
>     Couldn't register hvc console driver
>     virtio-ports vport0p1: error -16 allocating hvc for port
> 
> Here we add an atomic_t to guarantee we'll never run hvc_init twice.
> 
> Cc: stable@...r.kernel.org  # v2.6.24+
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Fixes: 3e6c6f630a52 ("Delay creation of khcvd thread")
> Reported-by: Jim Somerville <Jim.Somerville@...driver.com>
> Tested-by: Jim Somerville <Jim.Somerville@...driver.com>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> ---
> 
> [Greg: I realize tty-next is closed; given that this is an ancient
>  bug, I don't see any real urgency here, so feel free to queue it
>  whenever/whereever is most convenient - assuming it is an OK fix.]

Looks ok, I'll queue it up after 3.14-rc1 is out, thanks.

greg k-h
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