Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
Mathias Nyman
authored
commit 72f68bf5 upstream. There's a small window where a USB 2 remote wake may be left unhandled due to a race between hub thread and xhci port event interrupt handler. When the resume event is detected in the xhci interrupt handler it kicks the hub timer, which should move the port from resume to U0 once resume has been signalled for long enough. To keep the hub "thread" running we set a bus_state->resuming_ports flag. This flag makes sure hub timer function kicks itself. checking this flag was not properly protected by the spinlock. Flag was copied to a local variable before lock was taken. The local variable was then checked later with spinlock held. If interrupt is handled right after copying the flag to the local variable we end up stopping the hub thread before it can handle the USB 2 resume. CPU0 CPU1 (hub thread) (xhci event handler) xhci_hub_status_data() status = bus_state->resuming_ports; <Interrupt> handle_port_status() spin_lock() bus_state->resuming_ports = 1 set_flag(HCD_FLAG_POLL_RH) spin_unlock() spin_lock() if (!status) clear_flag(HCD_FLAG_POLL_RH) spin_unlock() Fix this by taking the lock a bit earlier so that it covers the resuming_ports flag copy in the hub thread Cc: <stable@vger.kernel.org> Signed-off-by:Mathias Nyman <mathias.nyman@linux.intel.com> Link: https://lore.kernel.org/r/20210715150651.1996099-2-mathias.nyman@linux.intel.com Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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