linux-kernel - Re: [patch V2 01/15] PCI/switchtec: Fix init_completion race condition with poll

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Message-ID: <20200318212513.GA240916@google.com>
Date:   Wed, 18 Mar 2020 16:25:13 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Logan Gunthorpe <logang@...tatee.com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        linux-pci@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [patch V2 01/15] PCI/switchtec: Fix init_completion race
 condition with poll_wait()

On Wed, Mar 18, 2020 at 09:43:03PM +0100, Thomas Gleixner wrote:
> From: Logan Gunthorpe <logang@...tatee.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@...utronix.de>
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lkml.kernel.org/r/20200313183608.2646-1-logang@deltatee.com

Acked-by: Bjorn Helgaas <bhelgaas@...gle.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
> 
>