[PATCH v2] USB:gadget: Fix a warning while loading g_mass_storage

[Wei.Yang]

From: Yang Wei <Wei.Yang@xxxxxxxxxxxxx>

While loading g_mass_storage module, the following warning is triggered.

WARNING: at drivers/usb/gadget/composite.c:
usb_composite_setup_continue: Unexpected call
Modules linked in: fat vfat minix nls_cp437 nls_iso8859_1 g_mass_storage
[<800179cc>] (unwind_backtrace+0x0/0x104) from [<80619608>] (dump_stack+0x20/0x24)
[<80619608>] (dump_stack+0x20/0x24) from [<80025100>] (warn_slowpath_common+0x64/0x74)
[<80025100>] (warn_slowpath_common+0x64/0x74) from [<800251cc>] (warn_slowpath_fmt+0x40/0x48)
[<800251cc>] (warn_slowpath_fmt+0x40/0x48) from [<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage])
[<7f047774>] (usb_composite_setup_continue+0xb4/0xbc [g_mass_storage]) from [<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage])
[<7f047ad4>] (handle_exception+0x358/0x3e4 [g_mass_storage]) from [<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage])
[<7f048080>] (fsg_main_thread+0x520/0x157c [g_mass_storage]) from [<8004bc90>] (kthread+0x98/0x9c)
[<8004bc90>] (kthread+0x98/0x9c) from [<8000faec>] (kernel_thread_exit+0x0/0x8) 

The root cause is that  Robert once introduced the following patch to fix
disconnect handling of s3c-hsotg.
[
commit d18f7116a5ddb8263fe62b05ad63e5ceb5875791
Author: Robert Baldyga <r.baldyga@xxxxxxxxxxx>
Date:   Thu Nov 21 13:49:18 2013 +0100

    usb: gadget: s3c-hsotg: fix disconnect handling

	    This patch moves s3c_hsotg_disconnect function call from USBSusp interrupt
		handler to SET_ADDRESS request handler.

		It's because disconnected state can't be detected directly, because this
		hardware doesn't support Disconnected interrupt for device mode. For both
		Suspend and Disconnect events there is one interrupt USBSusp, but calling
		s3c_hsotg_disconnect from this interrupt handler causes config reset in
		composite layer, which is not undesirable for Suspended state.

		For this reason s3c_hsotg_disconnect is called from SET_ADDRESS request
		handler, which occurs always after disconnection, so we do disconnect
		immediately before we are connected again. It's probably only way we
		can do handle disconnection correctly.

Signed-off-by: Robert Baldyga <r.baldyga@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
Signed-off-by: Felipe Balbi <balbi@xxxxxx> 
]

So it also means that s3c_hsotg_disconnect is called from SET_ADDRESS request handler,
ultimately reset_config would finally be called, it raises a FSG_STATE_CONFIG_CHANGE exception,
and set common->new_fsg to NULL, and then wakes up fsg_main_thread to handle this exception.
After handling SET_ADDRESS, subsequently the irq hanler of s3c-hsotg would also invokes composite_setup()
function to handle USB_REQ_SET_CONFIGURATION request, set_config would be invoked, it
not only raises a FSG_STATE_CONFIG_CHANGE and set common->new_fsg to new_fsg but also makes
cdev->delayed_status plus one. If the execution ordering just likes the following scenario, the warning
would be triggered.

irq handler
 |
 |-> s3c_hsotg_disconnect()
       |
       |-> common->new_fsg = NULL
       |-> common->state = FSG_STATE_CONFIG
       |-> wakes up fsg_main_thread.
 |->set USB device address.

fsg_main_thread
             |
             |-> handle_exception
                     |
                     |-> common->state = FSG_STATE_IDLE
                     |-> do_set_interface()
 irq happens -------------->

irq handler needs to handle USB_REQ_SET_CONFIGURATION request
 |
 |-> set_config()
        |
        |-> common->new_fsg = new_fsg;
        |-> common->state = FSG_STATE_CONFIG
        |-> cdev->delayed_status++
        |-> wakes up fsg_main_thread

fsg_main_thread
             |
			 |-> Now the common->state = FSG_STATE_CONFIG and common->new_fsg is not equal to NULL
             |-> if(common->new_fsg)
                       |-> usb_composite_setup_continue()
                                      |-> cdev->delayed_status--
             |-> fsg_main_thread still finds the common->state is equal to FSG_STATE_IDLE
             |-> so it invokes handle_exception again, subsequently the usb_composite_setup_continue
             |-> is executed again. It would fininally results in the warning.

So we also need to define a variable(struct fsg_dev *new) and then save common->new_fsg
to it with the common->lock protection.

Signed-off-by: Yang Wei <Wei.Yang@xxxxxxxxxxxxx>
---
 drivers/usb/gadget/f_mass_storage.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

                Changes in v2:

                 Only rephrase the commit log to make sense this issue.
		
		Wei

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index b963939..e3b1798 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -2342,6 +2342,7 @@ static void handle_exception(struct fsg_common *common)
 	struct fsg_buffhd	*bh;
 	enum fsg_state		old_state;
 	struct fsg_lun		*curlun;
+	struct fsg_dev   *new;
 	unsigned int		exception_req_tag;
 
 	/*
@@ -2421,6 +2422,7 @@ static void handle_exception(struct fsg_common *common)
 		}
 		common->state = FSG_STATE_IDLE;
 	}
+	new = common->new_fsg;
 	spin_unlock_irq(&common->lock);
 
 	/* Carry out any extra actions required for the exception */
@@ -2460,8 +2462,8 @@ static void handle_exception(struct fsg_common *common)
 		break;
 
 	case FSG_STATE_CONFIG_CHANGE:
-		do_set_interface(common, common->new_fsg);
-		if (common->new_fsg)
+		do_set_interface(common, new);
+		if (new)
 			usb_composite_setup_continue(common->cdev);
 		break;
 
-- 
1.7.9.5

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