linux-kernel - [RESEND PATCH v2] usb: gadget: f_mass_storage: add missing memory barrier for thread_wakeup

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Date:	Thu, 23 May 2013 11:10:11 +0900 (JST)
From:	UCHINO Satoshi <satoshi.uchino@...hiba.co.jp>
To:	balbi@...com, linux-usb@...r.kernel.org
Cc:	mina86@...a86.com, stern@...land.harvard.edu,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RESEND PATCH v2] usb: gadget: f_mass_storage: add missing memory
 barrier for thread_wakeup_needed

Without this memory barrier, the file-storage thread may fail to
escape from the following while loop, because it may observe new
common->thread_wakeup_needed and old bh->state which are updated by
the callback functions.

	/* Wait for the CBW to arrive */
	while (bh->state != BUF_STATE_FULL) {
		rc = sleep_thread(common);
		if (rc)
			return rc;
	}

Cc: stable@...r.kernel.org
Signed-off-by: UCHINO Satoshi <satoshi.uchino@...hiba.co.jp>
Acked-by: Michal Nazarewicz <mina86@...a86.com>
---
Resending with revised to and cc list and Acked-by line.
Cf. http://marc.info/?l=linux-usb&m=136361467905630&w=2

 drivers/usb/gadget/f_mass_storage.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 97666e8..c35a9ec 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -413,6 +413,7 @@ static int fsg_set_halt(struct fsg_dev *fsg, struct usb_ep *ep)
 /* Caller must hold fsg->lock */
 static void wakeup_thread(struct fsg_common *common)
 {
+	smp_wmb();	/* ensure the write of bh->state is complete */
 	/* Tell the main thread that something has happened */
 	common->thread_wakeup_needed = 1;
 	if (common->thread_task)
@@ -632,6 +633,7 @@ static int sleep_thread(struct fsg_common *common)
 	}
 	__set_current_state(TASK_RUNNING);
 	common->thread_wakeup_needed = 0;
+	smp_rmb();	/* ensure the latest bh->state is visible */
 	return rc;
 }
 
-- 
1.7.4.1

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