linux-kernel - [PATCH v1] USB:gadget: Fix a warning while loading g_mass

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Date:	Tue, 3 Jun 2014 17:37:15 +0800
From:	<Wei.Yang@...driver.com>
To:	<balbi@...com>, <gregkh@...uxfoundation.org>
CC:	<wei.yang@...driver.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v1] USB:gadget: Fix a warning while loading g_mass_storage

From: Yang Wei <Wei.Yang@...driver.com>

While loading g_mass_storage module, the following warning is triggered.
In fact, it is more easy to reproduce it with RT kernel.

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 just likes the following scenario.

irq thread

composite_disconnect()
|
|->fsg_disable() fsg->common->new_fsg = NULL
                 and then wake fsg_main_thread
                 with seting common->state to
                 FSG_STATE_CONFIG_CHANGE.
                                                    fsg_main_thread
                                                    |
                                                    |->do_set_interface()
irq thread

set_config()
|
|->fsg_set_alt() fsg->common->new_fsg = new_fsg
                 and then also wake up fsg_main_thread
                 with setting common->state to
                 FSG_STATE_CONFIG_CHANGE.
                                                    |-> if(common->new_fsg)
		                                                 usb_composite_setup_continue()

In this case, fsg_main_thread would invoke usb_composite_setup_continue
twice, so the second call would trigger the above call trace, as we also
save common->new_fsg while changing the common->state.

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

		Hi All,

		This patch is based on git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-next branch,
		and is validated it with altera cyclone V board.

		Thanks
		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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