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

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Date:	Sun, 15 Jun 2014 10:40:30 +0800
From:	<Wei.Yang@...driver.com>
To:	<stern@...land.harvard.edu>, <mina86@...a86.com>
CC:	<wei.yang@...driver.com>, <balbi@...com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] 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.

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 the existing code fails to take into
account the possibility that common->new_fsg can change while
do_set_interface() is running, so the value of common->new_fsg
that gets tested after do_set_interface returns needs to be
the same as the value used by do_set_interface.

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

Changes in v3 ----> v4

move "new_fsg = common->new_fsg" out of comm->lock protection, and refine the commit log.

Thanks
Wei

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index b963939..a7e24c8 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_fsg;
 	unsigned int		exception_req_tag;
 
 	/*
@@ -2460,8 +2461,9 @@ 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)
+		new_fsg = common->new_fsg;
+		do_set_interface(common, new_fsg);
+		if (new_fsg)
 			usb_composite_setup_continue(common->cdev);
 		break;
 
-- 
1.7.9.5

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