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generic_permission() turned out to be costlier than expected. The reason is that acl_permission_check() performs owner checks that involve costly pointer dereferences. There's already code that skips expensive group checks if the group and other permission bits are the same wrt to the mask that is checked. This logic can be extended to also shortcut permission checking in acl_permission_check(). If the inode doesn't have POSIX ACLs than ownership doesn't matter. If there are no missing UGO permissions the permission check can be shortcut. Acked-by: Al Viro <viro@zeniv.linux.org.uk> Link: https://lore.kernel.org/all/CAHk-=wgXEoAOFRkDg+grxs+p1U+QjWXLixRGmYEfd=vG+OBuFw@mail.gmail.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Christian Brauner <brauner@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.