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It will frequently be the case that rcu_torture_boost() will get a ->start_gp_poll() cookie that needs almost all of the current grace period plus an additional grace period to elapse before ->poll_gp_state() will return true. It is quite possible that the current grace period will have (say) two seconds of stall by a CPU failing to pass through a quiescent state, followed by 300 milliseconds of delay due to a preempted reader. The next grace period might suffer only one second of stall by a CPU, followed by another 300 milliseconds of delay due to a preempted reader. This is an example of RCU priority boosting doing its job, but the full elapsed time of 3.6 seconds exceeds the 3.5-second limit. In addition, there is no CPU stall in force at the 3.5-second mark, so this would nevertheless currently be counted as an RCU priority boosting failure. This commit therefore avoids this sort of false positive by resetting the gp_state_time timestamp any time that the current grace period is being blocked by a CPU. This results in extremely frequent calls to the ->check_boost_failed() function, so this commit provides a lockless fastpath that is selected by supplying a NULL CPU-number pointer. Signed-off-by: Paul E. McKenney <paulmck@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.