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@xxxxxxxxxxxxxxx # v2.6.24+
> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Fixes: 3e6c6f630a52 ("Delay creation of khcvd thread")
> Reported-by: Jim Somerville <Jim.Somerville@xxxxxxxxxxxxx>
> Tested-by: Jim Somerville <Jim.Somerville@xxxxxxxxxxxxx>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> ---
>
> [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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