On 14.05.2024 15:34:01, Vitor Soares wrote:
> > > +void mcp251xfd_tx_obj_write_sync(struct work_struct *ws)
> > > +{
> > > + struct mcp251xfd_priv *priv = container_of(ws, struct
> > > mcp251xfd_priv,
> > > + tx_work);
> > > + struct mcp251xfd_tx_obj *tx_obj = priv->tx_work_obj;
> > > + struct mcp251xfd_tx_ring *tx_ring = priv->tx;
> > > + int err;
> > > +
> > > + err = spi_sync(priv->spi, &tx_obj->msg);
> > > + if (err)
> > > + mcp251xfd_tx_failure_drop(priv, tx_ring, err);
> > > +
> > > + priv->tx_work_obj = NULL;
> >
> > Race condition:
> > - after spi_sync() the CAN frame is send
> > - after the TX complete IRQ the TX queue is restarted
> > - the xmit handler might get BUSY
> > - fill the tx_work_obj again
You can avoid the race condition by moving "priv->tx_work_obj = NULL;"
in front of the "spi_sync();". Right?
> > > +}
> > > +
> > > static int mcp251xfd_tx_obj_write(const struct mcp251xfd_priv *priv,
> > > struct mcp251xfd_tx_obj *tx_obj)
> > > {
> > > @@ -175,7 +210,7 @@ netdev_tx_t mcp251xfd_start_xmit(struct sk_buff *skb,
> > > if (can_dev_dropped_skb(ndev, skb))
> > > return NETDEV_TX_OK;
> > >
> > > - if (mcp251xfd_tx_busy(priv, tx_ring))
> > > + if (mcp251xfd_tx_busy(priv, tx_ring) || priv->tx_work_obj)
> >
> > This should not happen, but better save than sorry.
>
> As there is the race condition you mentioned above, on this condition:
> priv->tx_work_obj = tx_obj --> xmit will return NETDEV_TX_BUSY
>
> or
>
> priv->tx_work_obj = NULL --> It goes through the rest of the code or
> the workqueue may sleep after setting tx_work_obj to NULL. Should I
> use work_busy() here instead or do you have another suggestion?
Yes, introduce mcp251xfd_work_busy().
I'm not sure what happens if the xmit is called between the
"priv->tx_work_obj = NULL" and the end of the work. Will queue_work()
return false, as the queue is still running?
> Everything else is clear to me and I'm addressing it for the v6.
Marc
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