Running io_watchdog_func() while ohci_urb_enqueue() is running can
cause a race condition where ohci->prev_frame_no is corrupted and the
watchdog can mis-detect following error:
ohci-platform 664a0800.usb: frame counter not updating; disabled
ohci-platform 664a0800.usb: HC died; cleaning up
Specifically, following scenario causes a race condition:
1. ohci_urb_enqueue() calls spin_lock_irqsave(&ohci->lock, flags)
and enters the critical section
2. ohci_urb_enqueue() calls timer_pending(&ohci->io_watchdog) and it
returns false
3. ohci_urb_enqueue() sets ohci->prev_frame_no to a frame number
read by ohci_frame_no(ohci)
4. ohci_urb_enqueue() schedules io_watchdog_func() with mod_timer()
5. ohci_urb_enqueue() calls spin_unlock_irqrestore(&ohci->lock,
flags) and exits the critical section
6. Later, ohci_urb_enqueue() is called
7. ohci_urb_enqueue() calls spin_lock_irqsave(&ohci->lock, flags)
and enters the critical section
8. The timer scheduled on step 4 expires and io_watchdog_func() runs
9. io_watchdog_func() calls spin_lock_irqsave(&ohci->lock, flags)
and waits on it because ohci_urb_enqueue() is already in the
critical section on step 7
10. ohci_urb_enqueue() calls timer_pending(&ohci->io_watchdog) and it
returns false
11. ohci_urb_enqueue() sets ohci->prev_frame_no to new frame number
read by ohci_frame_no(ohci) because the frame number proceeded
between step 3 and 6
12. ohci_urb_enqueue() schedules io_watchdog_func() with mod_timer()
13. ohci_urb_enqueue() calls spin_unlock_irqrestore(&ohci->lock,
flags) and exits the critical section, then wake up
io_watchdog_func() which is waiting on step 9
14. io_watchdog_func() enters the critical section
15. io_watchdog_func() calls ohci_frame_no(ohci) and set frame_no
variable to the frame number
16. io_watchdog_func() compares frame_no and ohci->prev_frame_no
On step 16, because this calling of io_watchdog_func() is scheduled on
step 4, the frame number set in ohci->prev_frame_no is expected to the
number set on step 3. However, ohci->prev_frame_no is overwritten on
step 11. Because step 16 is executed soon after step 11, the frame
number might not proceed, so ohci->prev_frame_no must equals to
frame_no.
To address above scenario, this patch introduces timer_running flag to
ohci_hcd structure. Setting true to ohci->timer_running indicates
io_watchdog_func() is scheduled or is running. ohci_urb_enqueue()
checks the flag when it schedules the watchdog (step 4 and 12 above),
so ohci->prev_frame_no is not overwritten while io_watchdog_func() is
running.
Author: Yoshida, Shigeru <Shigeru.Yoshida@xxxxxxxxxxxxx>
Signed-off-by: Haiqing Bai <Haiqing.Bai@xxxxxxxxxxxxx>
---
drivers/usb/host/ohci-hcd.c | 7 +++++++
drivers/usb/host/ohci-hub.c | 4 +++-
drivers/usb/host/ohci.h | 1 +
3 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
index ee9676349333..2c7fa0c05854 100644
--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -233,10 +233,12 @@ static int ohci_urb_enqueue (
/* Start up the I/O watchdog timer, if it's not running */
if (!timer_pending(&ohci->io_watchdog) &&
list_empty(&ohci->eds_in_use) &&
+ !ohci->timer_running &&
!(ohci->flags & OHCI_QUIRK_QEMU)) {
ohci->prev_frame_no = ohci_frame_no(ohci);
mod_timer(&ohci->io_watchdog,
jiffies + IO_WATCHDOG_DELAY);
+ ohci->timer_running = 1;
}
list_add(&ed->in_use_list, &ohci->eds_in_use);
@@ -501,6 +503,7 @@ static int ohci_init (struct ohci_hcd *ohci)
return 0;
timer_setup(&ohci->io_watchdog, io_watchdog_func, 0);
+ ohci->timer_running = 0;
ohci->hcca = dma_alloc_coherent (hcd->self.controller,
sizeof(*ohci->hcca), &ohci->hcca_dma, GFP_KERNEL);
@@ -732,6 +735,7 @@ static void io_watchdog_func(struct timer_list *t)
struct td *td, *td_start, *td_next;
unsigned frame_no;
unsigned long flags;
+ int timer_running = 0;
spin_lock_irqsave(&ohci->lock, flags);
@@ -841,10 +845,12 @@ static void io_watchdog_func(struct timer_list *t)
&ohci->regs->donehead);
mod_timer(&ohci->io_watchdog,
jiffies + IO_WATCHDOG_DELAY);
+ timer_running = 1;
}
}
done:
+ ohci->timer_running = timer_running;
spin_unlock_irqrestore(&ohci->lock, flags);
}
@@ -973,6 +979,7 @@ static void ohci_stop (struct usb_hcd *hcd)
if (quirk_nec(ohci))
flush_work(&ohci->nec_work);
del_timer_sync(&ohci->io_watchdog);
+ ohci->timer_running = 0;
ohci_writel (ohci, OHCI_INTR_MIE, &ohci->regs->intrdisable);
ohci_usb_reset(ohci);
diff --git a/drivers/usb/host/ohci-hub.c b/drivers/usb/host/ohci-hub.c
index fb7aaa3b9d06..2aa21ee39cc2 100644
--- a/drivers/usb/host/ohci-hub.c
+++ b/drivers/usb/host/ohci-hub.c
@@ -311,8 +311,10 @@ static int ohci_bus_suspend (struct usb_hcd *hcd)
rc = ohci_rh_suspend (ohci, 0);
spin_unlock_irq (&ohci->lock);
- if (rc == 0)
+ if (rc == 0) {
del_timer_sync(&ohci->io_watchdog);
+ ohci->timer_running = 0;
+ }
return rc;
}
diff --git a/drivers/usb/host/ohci.h b/drivers/usb/host/ohci.h
index 508a803139dd..84f96558d667 100644
--- a/drivers/usb/host/ohci.h
+++ b/drivers/usb/host/ohci.h
@@ -427,6 +427,7 @@ struct ohci_hcd {
unsigned wdh_cnt, prev_wdh_cnt;
u32 prev_donehead;
struct timer_list io_watchdog;
+ int timer_running;
struct work_struct nec_work; /* Worker for NEC quirk */
--
2.11.0
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