linux-kernel - Re: [PATCH] usb: typec: displayport: Fix potential deadlock

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Message-ID: <aFqu7jvCwajL2OOE@kuha.fi.intel.com>
Date: Tue, 24 Jun 2025 16:58:06 +0300
From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To: Andrei Kuchynski <akuchynski@...omium.org>
Cc: Jos Wang <joswang@...ovo.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] usb: typec: displayport: Fix potential deadlock

On Tue, Jun 24, 2025 at 01:32:46PM +0000, Andrei Kuchynski wrote:
> The deadlock can occur due to a recursive lock acquisition of
> `cros_typec_altmode_data::mutex`.
> The call chain is as follows:
> 1. cros_typec_altmode_work() acquires the mutex
> 2. typec_altmode_vdm() -> dp_altmode_vdm() ->
> 3. typec_altmode_exit() -> cros_typec_altmode_exit()
> 4. cros_typec_altmode_exit() attempts to acquire the mutex again
> 
> To prevent this, defer the `typec_altmode_exit()` call by scheduling
> it rather than calling it directly from within the mutex-protected
> context.
> 
> Cc: stable@...r.kernel.org
> Fixes: b4b38ffb38c9 ("usb: typec: displayport: Receive DP Status Update NAK request exit dp altmode")
> Signed-off-by: Andrei Kuchynski <akuchynski@...omium.org>

Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  drivers/usb/typec/altmodes/displayport.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index b09b58d7311d..2abbe4de3216 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -394,8 +394,7 @@ static int dp_altmode_vdm(struct typec_altmode *alt,
>  	case CMDT_RSP_NAK:
>  		switch (cmd) {
>  		case DP_CMD_STATUS_UPDATE:
> -			if (typec_altmode_exit(alt))
> -				dev_err(&dp->alt->dev, "Exit Mode Failed!\n");
> +			dp->state = DP_STATE_EXIT;
>  			break;
>  		case DP_CMD_CONFIGURE:
>  			dp->data.conf = 0;

-- 
heikki