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BPF programs require to run on one CPU to completion as they use per CPU storage, but according to Alexei they don't need reentrancy protection as obviously BPF programs running in thread context can always be 'preempted' by hard and soft interrupts and instrumentation and the same program can run concurrently on a different CPU. The currently used mechanism to ensure CPUness is to wrap the invocation into a preempt_disable/enable() pair. Disabling preemption is also disabling migration for a task. preempt_disable/enable() is used because there is no explicit way to reliably disable only migration. Provide a separate macro to invoke a BPF program which can be used in migrateable task context. It wraps BPF_PROG_RUN() in a migrate_disable/enable() pair which maps on non RT enabled kernels to preempt_disable/enable(). On RT enabled kernels this merely disables migration. Both methods ensure that the invoked BPF program runs on one CPU to completion. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200224145643.474592620@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 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.