98482377dc
The widget_mutex was introduced to serialize callers to
hda_widget_sysfs_{re}init. However, its protection of the sysfs widget array
is incomplete. For example, it is acquired around the call to
hda_widget_sysfs_reinit(), which actually creates the new array, but isn't
still acquired when codec->num_nodes and codec->start_nid is updated. So
the lock ensures one thread sets up the new array at a time, but doesn't
ensure which thread's value will end up in codec->num_nodes. If a larger
num_nodes wins but a smaller array was set up, the next call to
refresh_widgets() will touch free memory as it iterates over codec->num_nodes
that aren't there.
The widget_lock really protects both the tree as well as codec->num_nodes,
start_nid, and end_nid, so make sure it's held across that update. It should
also be held during snd_hdac_get_sub_nodes(), so that a very old read from that
function doesn't end up clobbering a later update.
Fixes: ed180abba7f1 ("ALSA: hda: Fix race between creating and refreshing sysfs entries")
Signed-off-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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.