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[ Upstream commitdedab69fd6] Set em485->active_timer = NULL isn't always enough to take out the stop timer. While there is a check that it acts in the right state (i.e. waiting for RTS-after-send to pass after sending some chars) but the following might happen: - CPU1: some chars send, shifter becomes empty, stop tx timer armed - CPU0: more chars send before RTS-after-send expired - CPU0: shifter empty irq, port lock taken - CPU1: tx timer triggers, waits for port lock - CPU0: em485->active_timer = &em485->stop_tx_timer, hrtimer_start(), releases lock() - CPU1: get lock, see em485->active_timer == &em485->stop_tx_timer, tear down RTS too early This fix bases on research done by Steffen Trumtrar. Fixes:b86f86e8e7("serial: 8250: fix potential deadlock in rs485-mode") Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Link: https://lore.kernel.org/r/20220215160236.344236-1-u.kleine-koenig@pengutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.