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[ Upstream commit 4a56a478a5 ]
If fsg_disable() and fsg_set_alt() are called too closely to each
other (for example due to a quick reset/reconnect), what can happen
is that fsg_set_alt sets common->new_fsg from an interrupt while
handle_exception is trying to process the config change caused by
fsg_disable():
fsg_disable()
...
handle_exception()
sets state back to FSG_STATE_NORMAL
hasn't yet called do_set_interface()
or is inside it.
---> interrupt
fsg_set_alt
sets common->new_fsg
queues a new FSG_STATE_CONFIG_CHANGE
<---
Now, the first handle_exception can "see" the updated
new_fsg, treats it as if it was a fsg_set_alt() response,
call usb_composite_setup_continue() etc...
But then, the thread sees the second FSG_STATE_CONFIG_CHANGE,
and goes back down the same path, wipes and reattaches a now
active fsg, and .. calls usb_composite_setup_continue() which
at this point is wrong.
Not only we get a backtrace, but I suspect the second set_interface
wrecks some state causing the host to get upset in my case.
This fixes it by replacing "new_fsg" by a "state argument" (same
principle) which is set in the same lock section as the state
update, and retrieved similarly.
That way, there is never any discrepancy between the dequeued
state and the observed value of it. We keep the ability to have
the latest reconfig operation take precedence, but we guarantee
that once "dequeued" the argument (new_fsg) will not be clobbered
by any new event.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.