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

From: Bjorn Helgaas <[email-masked]>
Date: Wed, 18 Mar 2020 16:25:13 -0500

On Wed, Mar 18, 2020 at 09:43:03PM +0100, Thomas Gleixner wrote:
> From: Logan Gunthorpe <[email-masked]>
> 
> 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 <[email-masked]>
> Signed-off-by: Logan Gunthorpe <[email-masked]>
> Signed-off-by: Thomas Gleixner <[email-masked]>
> Link: https://lkml.kernel.org/r/[email-masked]

Acked-by: Bjorn Helgaas <[email-masked]>

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
> 
>