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A pair of matching srcu_read_lock() and srcu_read_unlock() invocations must take place within the same context, for example, within the same task. Otherwise, lockdep complains, as is the right thing to do for most use cases. However, there are use cases involving asynchronous I/O where the SRCU reader needs to begin on one task and end on another. This commit therefore supplies the semaphore-like srcu_down_read() and srcu_up_read(), which act like srcu_read_lock() and srcu_read_unlock(), but permitting srcu_up_read() to be invoked in a different context than was the matching srcu_down_read(). Neither srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler. Reported-by: Jan Kara <jack@suse.cz> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Tested-by: Amir Goldstein <amir73il@gmail.com>
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.