On Wed, 25 May 2016, Bin Liu wrote:
> [ 40.467381] =============================================
> [ 40.473013] [ INFO: possible recursive locking detected ]
> [ 40.478651] 4.6.0-08691-g7f3db9a #37 Not tainted
> [ 40.483466] ---------------------------------------------
> [ 40.489098] usb/733 is trying to acquire lock:
> [ 40.493734] (&(&dev->lock)->rlock){-.....}, at: [<bf129288>] ep0_complete+0x18/0xdc [gadgetfs]
> [ 40.502882]
> [ 40.502882] but task is already holding lock:
> [ 40.508967] (&(&dev->lock)->rlock){-.....}, at: [<bf12a420>] ep0_read+0x20/0x5e0 [gadgetfs]
> [ 40.517811]
> [ 40.517811] other info that might help us debug this:
> [ 40.524623] Possible unsafe locking scenario:
> [ 40.524623]
> [ 40.530798] CPU0
> [ 40.533346] ----
> [ 40.535894] lock(&(&dev->lock)->rlock);
> [ 40.540088] lock(&(&dev->lock)->rlock);
> [ 40.544284]
> [ 40.544284] *** DEADLOCK ***
> [ 40.544284]
> [ 40.550461] May be due to missing lock nesting notation
> [ 40.550461]
> [ 40.557544] 2 locks held by usb/733:
> [ 40.561271] #0: (&f->f_pos_lock){+.+.+.}, at: [<c02a6114>] __fdget_pos+0x40/0x48
> [ 40.569219] #1: (&(&dev->lock)->rlock){-.....}, at: [<bf12a420>] ep0_read+0x20/0x5e0 [gadgetfs]
> [ 40.578523]
> [ 40.578523] stack backtrace:
> [ 40.583075] CPU: 0 PID: 733 Comm: usb Not tainted 4.6.0-08691-g7f3db9a #37
> [ 40.590246] Hardware name: Generic AM33XX (Flattened Device Tree)
> [ 40.596625] [<c010ffbc>] (unwind_backtrace) from [<c010c1bc>] (show_stack+0x10/0x14)
> [ 40.604718] [<c010c1bc>] (show_stack) from [<c04207fc>] (dump_stack+0xb0/0xe4)
> [ 40.612267] [<c04207fc>] (dump_stack) from [<c01886ec>] (__lock_acquire+0xf68/0x1994)
> [ 40.620440] [<c01886ec>] (__lock_acquire) from [<c0189528>] (lock_acquire+0xd8/0x238)
> [ 40.628621] [<c0189528>] (lock_acquire) from [<c06ad6b4>] (_raw_spin_lock_irqsave+0x38/0x4c)
> [ 40.637440] [<c06ad6b4>] (_raw_spin_lock_irqsave) from [<bf129288>] (ep0_complete+0x18/0xdc [gadgetfs])
> [ 40.647339] [<bf129288>] (ep0_complete [gadgetfs]) from [<bf10a728>] (musb_g_giveback+0x118/0x1b0 [musb_hdrc])
> [ 40.657842] [<bf10a728>] (musb_g_giveback [musb_hdrc]) from [<bf108768>] (musb_g_ep0_queue+0x16c/0x188 [musb_hdrc])
> [ 40.668772] [<bf108768>] (musb_g_ep0_queue [musb_hdrc]) from [<bf12a944>] (ep0_read+0x544/0x5e0 [gadgetfs])
> [ 40.678963] [<bf12a944>] (ep0_read [gadgetfs]) from [<c0284470>] (__vfs_read+0x20/0x110)
> [ 40.687414] [<c0284470>] (__vfs_read) from [<c0285324>] (vfs_read+0x88/0x114)
> [ 40.694864] [<c0285324>] (vfs_read) from [<c0286150>] (SyS_read+0x44/0x9c)
> [ 40.702051] [<c0286150>] (SyS_read) from [<c0107820>] (ret_fast_syscall+0x0/0x1c)
>
> Cc: <stable@xxxxxxxxxxxxxxx> # v3.16+
> Signed-off-by: Bin Liu <b-liu@xxxxxx>
> ---
> drivers/usb/gadget/legacy/inode.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
> index e64479f..1251e1d 100644
> --- a/drivers/usb/gadget/legacy/inode.c
> +++ b/drivers/usb/gadget/legacy/inode.c
> @@ -938,8 +938,10 @@ ep0_read (struct file *fd, char __user *buf, size_t len, loff_t *ptr)
> struct usb_ep *ep = dev->gadget->ep0;
> struct usb_request *req = dev->req;
>
> + spin_unlock_irq (&dev->lock);
> if ((retval = setup_req (ep, req, 0)) == 0)
> retval = usb_ep_queue (ep, req, GFP_ATOMIC);
> + spin_lock_irq (&dev->lock);
Since you are enabling IRQs around this call to usb_ep_queue(), the
last argument should be changed to GFP_KERNEL.
> dev->state = STATE_DEV_CONNECTED;
>
> /* assume that was SET_CONFIGURATION */
You missed two other deadlock sources just like this one, in
gadgetfs_setup(): the two calls to usb_ep_queue() following the
"delegate:" statement label.
Alan Stern
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