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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> |
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| kernel | ||
| lib | ||
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| net | ||
| samples | ||
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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.