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When a single thread is sending out data over the gadget serial port,
gs_start_tx() will be called both from the sender context and from the
write completion. Since the port lock is released before the packet is
queued, the order in which the URBs are submitted is not guaranteed.
E.g.
sending thread completion (interrupt)
gs_write()
LOCK
gs_write_complete()
LOCK (wait)
gs_start_tx()
req1 = list_entry(pool->next)
UNLOCK
LOCK (acquired)
gs_start_tx()
req2 = list_entry(pool->next)
UNLOCK
usb_ep_queue(req2)
usb_ep_queue(req1)
I.e., req2 is submitted before req1 but it contains the data that
comes after req1.
To reproduce, use SMP with sending thread and completion pinned to
different CPUs, or use PREEMPT_RT, and add the following delay just
before the call to usb_ep_queue():
if (port->write_started > 0 && !list_empty(pool))
udelay(1000);
To work around this problem, make sure that only one thread is running
through the gs_start_tx() loop with an extra flag write_busy. Since
gs_start_tx() is always called with the port lock held, no further
synchronisation is needed. The original caller will continue through
the loop when the request was successfully submitted.
Signed-off-by: Philip Oberstaller <Philip.Oberstaller@septentrio.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Felipe Balbi <balbi@ti.com>
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| .. | ||
| atm | ||
| c67x00 | ||
| chipidea | ||
| class | ||
| common | ||
| core | ||
| dwc2 | ||
| dwc3 | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| isp1760 | ||
| misc | ||
| mon | ||
| musb | ||
| phy | ||
| renesas_usbhs | ||
| serial | ||
| storage | ||
| 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.