f6f4ec00b5
When requeuing to a PI futex, then the requeue code tries to trylock the PI futex on behalf of the topmost waiter on the inner 'waitqueue' futex. If that succeeds, then PI state has to be allocated in order to requeue further waiters to the PI futex. The comment and the code are confusing, as the PI state allocation uses lookup_pi_state(), which either attaches to an existing waiter or to the owner. As the PI futex was just acquired, there cannot be a waiter on the PI futex because the hash bucket lock is held. Clarify the comment and use attach_to_pi_owner() directly. As the task on which behalf the PI futex has been acquired is guaranteed to be alive and not exiting, this call must succeed. Add a WARN_ON() in case that fails. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210815211305.305142462@linutronix.de
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.