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3253cb49cb
softirqs are preemptible on PREEMPT_RT. There is synchronisation between individual sections which disable bottom halves. This in turn means that a forced threaded interrupt cannot preempt another forced threaded interrupt. Instead it will PI-boost the other handler and wait for its completion. This is required because code within a softirq section is assumed to be non-preemptible and may expect exclusive access to per-CPU resources such as variables or pinned timers. Code with such expectation has been identified and updated to use local_lock_nested_bh() for locking of the per-CPU resource. This means the softirq lock can be removed. Disable the softirq synchronization, but add a new config switch CONFIG_PREEMPT_RT_NEEDS_BH_LOCK which allows to re-enable the synchronized behavior in case that there are issues, which haven't been detected yet. The softirq_ctrl.cnt accounting remains to let the NOHZ code know if softirqs are currently handled. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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.