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Commit6cc8e74308("loop: scale loop device by introducing per device lock") re-opened a race window for NULL pointer dereference at loop_validate_file() where commit310ca162d7("block/loop: Use global lock for ioctl() operation.") has closed. Although we need to guarantee that other loop devices will not change during traversal, we can't take remote "struct loop_device"->lo_mutex inside loop_validate_file() in order to avoid AB-BA deadlock. Therefore, introduce a global lock dedicated for loop_validate_file() which is conditionally taken before local "struct loop_device"->lo_mutex is taken. Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Fixes:6cc8e74308("loop: scale loop device by introducing per device lock") Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.