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Yanfei reported that it is possible to loose HANDOFF when we race with mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At that point anybody can steal it, losing HANDOFF in the process. If this happens often enough, we can in fact starve the top waiter. Solve this by folding the 'set HANDOFF' operation into the trylock operation, such that either we acquire the lock, or it gets HANDOFF set. This avoids having HANDOFF set on an unlocked mutex. Reported-by: Yanfei Xu <yanfei.xu@windriver.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Waiman Long <longman@redhat.com> Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com> Link: https://lore.kernel.org/r/20210630154114.958507900@infradead.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.