Re: [patch V2 01/15] PCI/switchtec: Fix init_completion race condition with poll_wait()

Bjorn Helgaas
2020-03-18T21:25:19Z

On Wed, Mar 18, 2020 at 09:43:03PM +0100, Thomas Gleixner wrote:
> From: Logan Gunthorpe <logang@deltatee.com>
>
> The call to init_completion() in mrpc_queue_cmd() can theoretically
> race with the call to poll_wait() in switchtec_dev_poll().
>
> poll() write()
> switchtec_dev_poll() switchtec_dev_write()
> poll_wait(&s->comp.wait); mrpc_queue_cmd()
> init_completion(&s->comp)
> init_waitqueue_head(&s->comp.wait)
>
> To my knowledge, no one has hit this bug.
>
> Fix this by using reinit_completion() instead of init_completion() in
> mrpc_queue_cmd().
>
> Fixes: 080b47def5e5 ("MicroSemi Switchtec management interface driver")
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Link: https://lkml.kernel.org/r/20200313183608.2646-1-logang@deltatee.com

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

Not because I understand and have reviewed this, but because I trust
you to do the right thing and it belongs with the rest of the series.

> ---
> drivers/pci/switch/switchtec.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
> index a823b4b8ef8a..81dc7ac01381 100644
> --- a/drivers/pci/switch/switchtec.c
> +++ b/drivers/pci/switch/switchtec.c
> @@ -175,7 +175,7 @@ static int mrpc_queue_cmd(struct switchtec_user *stuser)
> kref_get(&stuser->kref);
> stuser->read_len = sizeof(stuser->data);
> stuser_set_state(stuser, MRPC_QUEUED);
> - init_completion(&stuser->comp);
> + reinit_completion(&stuser->comp);
> list_add_tail(&stuser->list, &stdev->mrpc_queue);
>
> mrpc_cmd_submit(stdev);
> --
> 2.20.1
>
>