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Message-Id: <8b1201dc7554a2ab3ca555a2b6e2747761603d19.1649310812.git.duoming@zju.edu.cn>
Date: Thu, 7 Apr 2022 14:33:18 +0800
From: Duoming Zhou <duoming@....edu.cn>
To: linux-kernel@...r.kernel.org
Cc: chris@...kel.net, jcmvbkbc@...il.com, mustafa.ismail@...el.com,
shiraz.saleem@...el.com, jgg@...pe.ca, wg@...ndegger.com,
mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
pabeni@...hat.com, jes@...ined-monkey.org,
gregkh@...uxfoundation.org, jirislaby@...nel.org,
alexander.deucher@....com, linux-xtensa@...ux-xtensa.org,
linux-rdma@...r.kernel.org, linux-can@...r.kernel.org,
netdev@...r.kernel.org, linux-hippi@...site.dk,
linux-staging@...ts.linux.dev, linux-serial@...r.kernel.org,
linux-usb@...r.kernel.org, Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH 02/11] drivers: usb: host: Fix deadlock in oxu_bus_suspend()
There is a deadlock in oxu_bus_suspend(), which is shown below:
(Thread 1) | (Thread 2)
| timer_action()
oxu_bus_suspend() | mod_timer()
spin_lock_irq() //(1) | (wait a time)
... | oxu_watchdog()
del_timer_sync() | spin_lock_irq() //(2)
(wait timer to stop) | ...
We hold oxu->lock in position (1) of thread 1, and use
del_timer_sync() to wait timer to stop, but timer handler
also need oxu->lock in position (2) of thread 2. As a result,
oxu_bus_suspend() will block forever.
This patch extracts del_timer_sync() from the protection of
spin_lock_irq(), which could let timer handler to obtain
the needed lock.
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
drivers/usb/host/oxu210hp-hcd.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/usb/host/oxu210hp-hcd.c b/drivers/usb/host/oxu210hp-hcd.c
index b741670525e..ee403df3309 100644
--- a/drivers/usb/host/oxu210hp-hcd.c
+++ b/drivers/usb/host/oxu210hp-hcd.c
@@ -3909,8 +3909,10 @@ static int oxu_bus_suspend(struct usb_hcd *hcd)
}
}
+ spin_unlock_irq(&oxu->lock);
/* turn off now-idle HC */
del_timer_sync(&oxu->watchdog);
+ spin_lock_irq(&oxu->lock);
ehci_halt(oxu);
hcd->state = HC_STATE_SUSPENDED;
--
2.17.1
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