mainlining shenanigans
0f663729bb
Bugzilla #213839 reports a 7-port hub that doesn't work properly when devices are plugged into some of the ports; the kernel goes into an unending disconnect/reinitialize loop as shown in the bug report. This "7-port hub" comprises two four-port hubs with one plugged into the other; the failures occur when a device is plugged into one of the downstream hub's ports. (These hubs have other problems too. For example, they bill themselves as USB-2.0 compliant but they only run at full speed.) It turns out that the failures are caused by bugs in both the kernel and the hub. The hub's bug is that it reports a different bmAttributes value in its configuration descriptor following a remote wakeup (0xe0 before, 0xc0 after -- the wakeup-support bit has changed). The kernel's bug is inside the hub driver's resume handler. When hub_activate() sees that one of the hub's downstream ports got a wakeup request from a child device, it notes this fact by setting the corresponding bit in the hub->change_bits variable. But this variable is meant for connection changes, not wakeup events; setting it causes the driver to believe the downstream port has been disconnected and then connected again (in addition to having received a wakeup request). Because of this, the hub driver then tries to check whether the device currently plugged into the downstream port is the same as the device that had been attached there before. Normally this check succeeds and wakeup handling continues with no harm done (which is why the bug remained undetected until now). But with these dodgy hubs, the check fails because the config descriptor has changed. This causes the hub driver to reinitialize the child device, leading to the disconnect/reinitialize loop described in the bug report. The proper way to note reception of a downstream wakeup request is to set a bit in the hub->event_bits variable instead of hub->change_bits. That way the hub driver will realize that something has happened to the port but will not think the port and child device have been disconnected. This patch makes that change. Cc: <stable@vger.kernel.org> Tested-by: Jonathan McDowell <noodles@earth.li> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Link: https://lore.kernel.org/r/YdCw7nSfWYPKWQoD@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| README | ||
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.