This is a note to let you know that I've just added the patch titled
ohci-hcd: Fix race condition caused by ohci_urb_enqueue() and
to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From b2685bdacdaab065c172b97b55ab46c6be77a037 Mon Sep 17 00:00:00 2001
From: Shigeru Yoshida shigeru.yoshida@windriver.com Date: Fri, 2 Feb 2018 13:51:39 +0800 Subject: ohci-hcd: Fix race condition caused by ohci_urb_enqueue() and io_watchdog_func()
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(-)
diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c index ee9676349333..84f88fa411cd 100644 --- a/drivers/usb/host/ohci-hcd.c +++ b/drivers/usb/host/ohci-hcd.c @@ -74,6 +74,7 @@ static const char hcd_name [] = "ohci_hcd";
#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" @@ -231,7 +232,7 @@ 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 *ohci) return 0;
timer_setup(&ohci->io_watchdog, io_watchdog_func, 0); + 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(struct timer_list *t) 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(struct timer_list *t) } } 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(struct timer_list *t) }
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 *hcd) 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); diff --git a/drivers/usb/host/ohci-hub.c b/drivers/usb/host/ohci-hub.c index fb7aaa3b9d06..634f3c7bf774 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->prev_frame_no = IO_WATCHDOG_OFF; + } return rc; }