dc9217b69d
f_mass_storage has a memorry barrier issue with the sleep and wake functions that can cause a deadlock. This results in intermittent hangs during MSC file transfer. The host will reset the device after receiving no response to resume the transfer. This issue is seen when dwc3 is processing 2 transfer-in-progress events at the same time, invoking completion handlers for CSW and CBW. Also this issue occurs depending on the system timing and latency. To increase the chance to hit this issue, you can force dwc3 driver to wait and process those 2 events at once by adding a small delay (~100us) in dwc3_check_event_buf() whenever the request is for CSW and read the event count again. Avoid debugging with printk and ftrace as extra delays and memory barrier will mask this issue. Scenario which can lead to failure: ----------------------------------- 1) The main thread sleeps and waits for the next command in get_next_command(). 2) bulk_in_complete() wakes up main thread for CSW. 3) bulk_out_complete() tries to wake up the running main thread for CBW. 4) thread_wakeup_needed is not loaded with correct value in sleep_thread(). 5) Main thread goes to sleep again. The pattern is shown below. Note the 2 critical variables. * common->thread_wakeup_needed * bh->state CPU 0 (sleep_thread) CPU 1 (wakeup_thread) ============================== =============================== bh->state = BH_STATE_FULL; smp_wmb(); thread_wakeup_needed = 0; thread_wakeup_needed = 1; smp_rmb(); if (bh->state != BH_STATE_FULL) sleep again ... As pointed out by Alan Stern, this is an R-pattern issue. The issue can be seen when there are two wakeups in quick succession. The thread_wakeup_needed can be overwritten in sleep_thread, and the read of the bh->state maybe reordered before the write to thread_wakeup_needed. This patch applies full memory barrier smp_mb() in both sleep_thread() and wakeup_thread() to ensure the order which the thread_wakeup_needed and bh->state are written and loaded. However, a better solution in the future would be to use wait_queue method that takes care of managing memory barrier between waker and waiter. Cc: <stable@vger.kernel.org> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Thinh Nguyen <thinhn@synopsys.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> |
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| .. | ||
| atm | ||
| c67x00 | ||
| chipidea | ||
| class | ||
| common | ||
| core | ||
| dwc2 | ||
| dwc3 | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| isp1760 | ||
| misc | ||
| mon | ||
| mtu3 | ||
| musb | ||
| phy | ||
| renesas_usbhs | ||
| serial | ||
| storage | ||
| typec | ||
| usbip | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-skeleton.c | ||
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("hub_wq").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.