[PATCH v3] can: slcan: do not sleep with a spin lock held

[PATCH v3] can: slcan: do not sleep with a spin lock held

[Dario Binacchi]

We can't call close_candev() with a spin lock held, so release the lock
before calling it. After calling close_candev(), we can update the
fields of the private `struct can_priv' without having to acquire the
lock.

Fixes: c4e54b063f42f ("can: slcan: use CAN network device driver API")
Reported-by: kernel test robot <oliver.sang@intel.com>
Link: https://lore.kernel.org/linux-kernel/Ysrf1Yc5DaRGN1WE@xsang-OptiPlex-9020/
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

---

Changes in v3:
- Update the commit message.
- Reset sl->rcount and sl->xleft before releasing the spin lock.

Changes in v2:
- Release the lock just before calling the close_candev().

 drivers/net/can/slcan/slcan-core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
index 54d29a410ad5..d40ddc596596 100644
--- a/drivers/net/can/slcan/slcan-core.c
+++ b/drivers/net/can/slcan/slcan-core.c
@@ -689,15 +689,14 @@ static int slc_close(struct net_device *dev)
 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
 	}
 	netif_stop_queue(dev);
+	sl->rcount   = 0;
+	sl->xleft    = 0;
+	spin_unlock_bh(&sl->lock);
 	close_candev(dev);
 	sl->can.state = CAN_STATE_STOPPED;
 	if (sl->can.bittiming.bitrate == CAN_BITRATE_UNKNOWN)
 		sl->can.bittiming.bitrate = CAN_BITRATE_UNSET;
 
-	sl->rcount   = 0;
-	sl->xleft    = 0;
-	spin_unlock_bh(&sl->lock);
-
 	return 0;
 }
 
-- 
2.32.0

Re: [PATCH v3] can: slcan: do not sleep with a spin lock held

[Souptick Joarder]

On Fri, Jul 15, 2022 at 1:00 PM Dario Binacchi
<dario.binacchi@amarulasolutions.com> wrote:
>
> We can't call close_candev() with a spin lock held, so release the lock
> before calling it. After calling close_candev(), we can update the
> fields of the private `struct can_priv' without having to acquire the
> lock.

But here we are updating private 'struct can_priv' before close_candev() while
taking the lock.  If we go by change logs, then spin_unlock_bh() need to called
before close_candev() and we can update the private 'struct can_priv'
in existing place.

>
> Fixes: c4e54b063f42f ("can: slcan: use CAN network device driver API")
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Link: https://lore.kernel.org/linux-kernel/Ysrf1Yc5DaRGN1WE@xsang-OptiPlex-9020/
> Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
>
> ---
>
> Changes in v3:
> - Update the commit message.
> - Reset sl->rcount and sl->xleft before releasing the spin lock.
>
> Changes in v2:
> - Release the lock just before calling the close_candev().
>
>  drivers/net/can/slcan/slcan-core.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
> index 54d29a410ad5..d40ddc596596 100644
> --- a/drivers/net/can/slcan/slcan-core.c
> +++ b/drivers/net/can/slcan/slcan-core.c
> @@ -689,15 +689,14 @@ static int slc_close(struct net_device *dev)
>                 clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
>         }
>         netif_stop_queue(dev);
> +       sl->rcount   = 0;
> +       sl->xleft    = 0;
> +       spin_unlock_bh(&sl->lock);
>         close_candev(dev);
>         sl->can.state = CAN_STATE_STOPPED;
>         if (sl->can.bittiming.bitrate == CAN_BITRATE_UNKNOWN)
>                 sl->can.bittiming.bitrate = CAN_BITRATE_UNSET;
>
> -       sl->rcount   = 0;
> -       sl->xleft    = 0;
> -       spin_unlock_bh(&sl->lock);
> -
>         return 0;
>  }
>
> --
> 2.32.0
>
>

Re: [PATCH v3] can: slcan: do not sleep with a spin lock held

[Dario Binacchi]

Hello Souptick,

On Thu, Jul 21, 2022 at 3:58 AM Souptick Joarder <jrdr.linux@gmail.com> wrote:
>
> On Fri, Jul 15, 2022 at 1:00 PM Dario Binacchi
> <dario.binacchi@amarulasolutions.com> wrote:
> >
> > We can't call close_candev() with a spin lock held, so release the lock
> > before calling it. After calling close_candev(), we can update the
> > fields of the private `struct can_priv' without having to acquire the
> > lock.
>
> But here we are updating private 'struct can_priv' before close_candev() while
> taking the lock.  If we go by change logs, then spin_unlock_bh() need to called
> before close_candev() and we can update the private 'struct can_priv'
> in existing place.

sl-> rcount and sl-> xleft are not part of 'struct can_priv' and can
be reset after
calling netif_stop_queu() because it inhibits any serial reception/transmission.

Thanks and regards,
Dario

>
> >
> > Fixes: c4e54b063f42f ("can: slcan: use CAN network device driver API")
> > Reported-by: kernel test robot <oliver.sang@intel.com>
> > Link: https://lore.kernel.org/linux-kernel/Ysrf1Yc5DaRGN1WE@xsang-OptiPlex-9020/
> > Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> >
> > ---
> >
> > Changes in v3:
> > - Update the commit message.
> > - Reset sl->rcount and sl->xleft before releasing the spin lock.
> >
> > Changes in v2:
> > - Release the lock just before calling the close_candev().
> >
> >  drivers/net/can/slcan/slcan-core.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/can/slcan/slcan-core.c b/drivers/net/can/slcan/slcan-core.c
> > index 54d29a410ad5..d40ddc596596 100644
> > --- a/drivers/net/can/slcan/slcan-core.c
> > +++ b/drivers/net/can/slcan/slcan-core.c
> > @@ -689,15 +689,14 @@ static int slc_close(struct net_device *dev)
> >                 clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
> >         }
> >         netif_stop_queue(dev);
> > +       sl->rcount   = 0;
> > +       sl->xleft    = 0;
> > +       spin_unlock_bh(&sl->lock);
> >         close_candev(dev);
> >         sl->can.state = CAN_STATE_STOPPED;
> >         if (sl->can.bittiming.bitrate == CAN_BITRATE_UNKNOWN)
> >                 sl->can.bittiming.bitrate = CAN_BITRATE_UNSET;
> >
> > -       sl->rcount   = 0;
> > -       sl->xleft    = 0;
> > -       spin_unlock_bh(&sl->lock);
> > -
> >         return 0;
> >  }
> >
> > --
> > 2.32.0
> >
> >



-- 

Dario Binacchi

Embedded Linux Developer

dario.binacchi@amarulasolutions.com

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