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The main purpose of the test is to demonstrate the lock problem for the free of bpf_timer under PREEMPT_RT. When freeing a bpf_timer which is running on other CPU in bpf_timer_cancel_and_free(), hrtimer_cancel() will try to acquire a spin-lock (namely softirq_expiry_lock), however the freeing procedure has already held a raw-spin-lock. The test first creates two threads: one to start timers and the other to free timers. The start-timers thread will start the timer and then wake up the free-timers thread to free these timers when the starts complete. After freeing, the free-timer thread will wake up the start-timer thread to complete the current iteration. A loop of 10 iterations is used. Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20250117101816.2101857-6-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@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 reStructuredText 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.