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commit797964253dupstream. In commit20ea1e7d13("file: always lock position for FMODE_ATOMIC_POS") we ended up always taking the file pos lock, because pidfd_getfd() could get a reference to the file even when it didn't have an elevated file count due to threading of other sharing cases. But Mateusz Guzik reports that the extra locking is actually measurable, so let's re-introduce the optimization, and only force the locking for directory traversal. Directories need the lock for correctness reasons, while regular files only need it for "POSIX semantics". Since pidfd_getfd() is about debuggers etc special things that are _way_ outside of POSIX, we can relax the rules for that case. Reported-by: Mateusz Guzik <mjguzik@gmail.com> Cc: Christian Brauner <brauner@kernel.org> Link: https://lore.kernel.org/linux-fsdevel/20230803095311.ijpvhx3fyrbkasul@f/ Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 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.