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Subject[PATCH 4.14 31/54] ohci-hcd: Fix race condition caused by ohci_urb_enqueue() and io_watchdog_func()
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shigeru Yoshida <shigeru.yoshida@windriver.com>

commit b2685bdacdaab065c172b97b55ab46c6be77a037 upstream.

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 a special sentinel
value IO_WATCHDOG_OFF and set this value to ohci->prev_frame_no when
the watchdog is not pending or running. When ohci_urb_enqueue()
schedules the watchdog (step 4 and 12 above), it compares
ohci->prev_frame_no to IO_WATCHDOG_OFF so that ohci->prev_frame_no is
not overwritten while io_watchdog_func() is running.

Signed-off-by: Shigeru Yoshida <Shigeru.Yoshida@windriver.com>
Signed-off-by: Haiqing Bai <Haiqing.Bai@windriver.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/host/ohci-hcd.c | 10 +++++++---
drivers/usb/host/ohci-hub.c | 4 +++-
2 files changed, 10 insertions(+), 4 deletions(-)

--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -73,6 +73,7 @@ static const char hcd_name [] = "ohci_hc

#define STATECHANGE_DELAY msecs_to_jiffies(300)
#define IO_WATCHDOG_DELAY msecs_to_jiffies(275)
+#define IO_WATCHDOG_OFF 0xffffff00

#include "ohci.h"
#include "pci-quirks.h"
@@ -230,7 +231,7 @@ static int ohci_urb_enqueue (
}

/* Start up the I/O watchdog timer, if it's not running */
- if (!timer_pending(&ohci->io_watchdog) &&
+ if (ohci->prev_frame_no == IO_WATCHDOG_OFF &&
list_empty(&ohci->eds_in_use) &&
!(ohci->flags & OHCI_QUIRK_QEMU)) {
ohci->prev_frame_no = ohci_frame_no(ohci);
@@ -501,6 +502,7 @@ static int ohci_init (struct ohci_hcd *o

setup_timer(&ohci->io_watchdog, io_watchdog_func,
(unsigned long) ohci);
+ ohci->prev_frame_no = IO_WATCHDOG_OFF;

ohci->hcca = dma_alloc_coherent (hcd->self.controller,
sizeof(*ohci->hcca), &ohci->hcca_dma, GFP_KERNEL);
@@ -730,7 +732,7 @@ static void io_watchdog_func(unsigned lo
u32 head;
struct ed *ed;
struct td *td, *td_start, *td_next;
- unsigned frame_no;
+ unsigned frame_no, prev_frame_no = IO_WATCHDOG_OFF;
unsigned long flags;

spin_lock_irqsave(&ohci->lock, flags);
@@ -835,7 +837,7 @@ static void io_watchdog_func(unsigned lo
}
}
if (!list_empty(&ohci->eds_in_use)) {
- ohci->prev_frame_no = frame_no;
+ prev_frame_no = frame_no;
ohci->prev_wdh_cnt = ohci->wdh_cnt;
ohci->prev_donehead = ohci_readl(ohci,
&ohci->regs->donehead);
@@ -845,6 +847,7 @@ static void io_watchdog_func(unsigned lo
}

done:
+ ohci->prev_frame_no = prev_frame_no;
spin_unlock_irqrestore(&ohci->lock, flags);
}

@@ -973,6 +976,7 @@ static void ohci_stop (struct usb_hcd *h
if (quirk_nec(ohci))
flush_work(&ohci->nec_work);
del_timer_sync(&ohci->io_watchdog);
+ ohci->prev_frame_no = IO_WATCHDOG_OFF;

ohci_writel (ohci, OHCI_INTR_MIE, &ohci->regs->intrdisable);
ohci_usb_reset(ohci);
--- a/drivers/usb/host/ohci-hub.c
+++ b/drivers/usb/host/ohci-hub.c
@@ -310,8 +310,10 @@ static int ohci_bus_suspend (struct usb_
rc = ohci_rh_suspend (ohci, 0);
spin_unlock_irq (&ohci->lock);

- if (rc == 0)
+ if (rc == 0) {
del_timer_sync(&ohci->io_watchdog);
+ ohci->prev_frame_no = IO_WATCHDOG_OFF;
+ }
return rc;
}


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