[LEDE-DEV] [BUG] [lantiq] xrx200 network driver sleeping with spinlock held

[John Crispin]

On 03/07/17 18:52, Andrea Merello wrote:
> Due to some OT reasons I'm compiling LEDE kernel (4.9.31) with several
> debug checks enabled, and I'm using it on a Lantiq xrx200 board
> (fritzbox 3370).
>
> I've hit a bug (among another one) in lantiq_xrx200.c network driver:
> in the xrx200_close() function we call napi_disable(), that could
> sleep, with priv->hw->chan[i].lock held, causing the kernel to
> complain [1].
>
> After a quick look at the code I couldn't convince myself about why we
> need to protect that specific code part with the lock. IMHO there
> seems no reason to protect the refcount variables, because AFAIK
> ndo_close() and ndo_open() callbacks are already called with a
> semaphore held. Neither I could figure out why napi_disable() have to
> be called with that lock held. I don't know about ltq_dma_close(), and
> whether your intention was to avoid races wrt housekeeping tasklet,
> but my speculation is that eventually the lock could be reduced to
> just that function [0].
>
> However, because I'm not familiar with this driver code, I really just
> wanted to point out the problem here, and hear from you :)
>
> Andrea
Hi Andrea,

patch looks correct can you please resend it in the correct format. the 
patch submission should contain a patch that adds the actual patch under 
target/linux/lantiq/patches...

additionally please make sure to add your Signed-off-by line to the patch

     John

> [0]
> --- a/drivers/net/ethernet/lantiq_xrx200.c
> +++ b/drivers/net/ethernet/lantiq_xrx200.c
> @@ -898,14 +898,15 @@ static int xrx200_close(struct net_device *dev)
>          for (i = 0; i < XRX200_MAX_DMA; i++) {
>                  if (!priv->hw->chan[i].dma.irq)
>                          continue;
> -               spin_lock_bh(&priv->hw->chan[i].lock);
> +
>                  priv->hw->chan[i].refcount--;
>                  if (!priv->hw->chan[i].refcount) {
>                          if (XRX200_DMA_IS_RX(i))
>                                  napi_disable(&priv->hw->chan[i].napi);
> +                       spin_lock_bh(&priv->hw->chan[i].lock);
>                          ltq_dma_close(&priv->hw->chan[XRX200_DMA_RX].dma);
> +                       spin_unlock_bh(&priv->hw->chan[i].lock);
>                  }
> -               spin_unlock_bh(&priv->hw->chan[i].lock);
>          }
>
>          return 0;
>
> [1]
> [    7.327061] BUG: sleeping function called from invalid context at
> net/core/dev.c:5144
> [    7.333555] in_atomic(): 1, irqs_disabled(): 0, pid: 534, name: ip
> [    7.339698] 2 locks held by ip/534:
> [    7.343111]  #0:  (rtnl_mutex){......}, at: [<8049a780>]
> devinet_ioctl+0x180/0x724
> [    7.350744]  #1:  (&(&ch->lock)->rlock){......}, at: [<803b303c>]
> xrx200_close+0xc4/0x150
> [    7.358942] CPU: 1 PID: 534 Comm: ip Not tainted 4.9.31 #0
> [    7.364351] Stack : 00000000 00000000 80e6c56a 0000002e 80573bb4
> 00000000 00000000 807a0000
> [    7.372697]         87d3716c 80795887 806f38bc 00000001 00000216
> 809041fc 00008914 7ff828fc
> [    7.381053]         7ff828bc 8007da38 00008914 7ff828fc 7ff828bc
> 8007da38 806faf04 8749dc6c
> [    7.389409]         00000001 800be57c 806f97e4 8749dc7c 00008914
> 80790000 7ff828bc 8749dc00
> [    7.397765]         00000000 00000000 00000000 00000000 00000000
> 00000000 00000000 00000000
> [    7.406121]         ...
> [    7.408560] Call Trace:
> [    7.411012] [<80010b38>] show_stack+0x50/0x84
> [    7.415397] [<802c0374>] dump_stack+0xd4/0x110
> [    7.419825] [<800569b0>] ___might_sleep+0xfc/0x11c
> [    7.424613] [<8041cf98>] napi_disable+0x3c/0x194
> [    7.429223] [<803b3078>] xrx200_close+0x100/0x150
> [    7.433917] [<80419f9c>] __dev_close_many+0xf4/0x128
> [    7.438885] [<8041a148>] __dev_close+0x30/0x50
> [    7.443315] [<80423c40>] __dev_change_flags+0xb8/0x174
> [    7.448456] [<80423d24>] dev_change_flags+0x28/0x70
> [    7.453339] [<8049a838>] devinet_ioctl+0x238/0x724
> [    7.458128] [<80400694>] sock_ioctl+0x2cc/0x32c
> [    7.462649] [<8011e840>] vfs_ioctl+0x20/0x40
> [    7.466902] [<8011f1f4>] do_vfs_ioctl+0x7e8/0x904
> [    7.471618] [<8011f360>] SyS_ioctl+0x50/0xa0
> [    7.475876] [<8001ad38>] syscall_common+0x34/0x58
>
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