| Message ID | 8b1201dc7554a2ab3ca555a2b6e2747761603d19.1649310812.git.duoming@zju.edu.cn (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | Fix deadlocks caused by del_timer_sync() | expand |
On 07.04.22 08:33, Duoming Zhou wrote: > 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. Good catch. > Signed-off-by: Duoming Zhou <duoming@zju.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; > What is the lock protecting at that stage? Why not just drop it earlier. Regards Oliver
Hello, On Thu, 7 Apr 2022 10:01:43 +0200 Oliver Neukum wrote: > On 07.04.22 08:33, Duoming Zhou wrote: > > 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. > Good catch. > > Signed-off-by: Duoming Zhou <duoming@zju.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; > > > > What is the lock protecting at that stage? Why not just drop it earlier. I think there is a race condition between oxu_bus_suspend() and oxu_stop(), so I think we could not drop the oxu->lock earlier. (Thread 1) | (Thread 2) oxu_bus_suspend() | oxu_stop() | hcd->state = HC_STATE_SUSPENDED; | spin_lock_irq(&oxu->lock); ... | writel(mask, &oxu->regs->intr_enable); | ... | writel(0, &oxu->regs->intr_enable); readl(&oxu->regs->intr_enable); | The oxu->regs->intr_enable is set to 0 in oxu_stop(), and the readl() in oxu_bus_suspend() will read the wrong value. Thanks a lot for your time and advice. If you have questions, welcome to ask me. Best regards, Duoming Zhou
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;
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@zju.edu.cn> --- drivers/usb/host/oxu210hp-hcd.c | 2 ++ 1 file changed, 2 insertions(+)