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commit 944d5fe50f3f03daacfea16300e656a1691c4a23 upstream. On some systems, sys_membarrier can be very expensive, causing overall slowdowns for everything. So put a lock on the path in order to serialize the accesses to prevent the ability for this to be called at too high of a frequency and saturate the machine. Reviewed-and-tested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Borislav Petkov <bp@alien8.de> Fixes:22e4ebb975("membarrier: Provide expedited private command") Fixes:c5f58bd58f("membarrier: Provide GLOBAL_EXPEDITED command") Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [ converted to explicit mutex_*() calls - cleanup.h is not in this stable branch - gregkh ] Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.