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Regular sleeping locks like mutexes, rtmutexes and rw_semaphores are always entering and leaving a blocking section with task state == TASK_RUNNING. On a non-RT kernel spinlocks and rwlocks never affect the task state, but on RT kernels these locks are converted to rtmutex based 'sleeping' locks. So in case of contention the task goes to block, which requires to carefully preserve the task state, and restore it after acquiring the lock taking regular wakeups for the task into account, which happened while the task was blocked. This state preserving is achieved by having a separate task state for blocking on a RT spin/rwlock and a saved_state field in task_struct along with careful handling of these wakeup scenarios in try_to_wake_up(). To avoid conditionals in the rtmutex code, store the wake state which has to be used for waking a lock waiter in rt_mutex_waiter which allows to handle the regular and RT spin/rwlocks by handing it to wake_up_state(). 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/20210815211303.079800739@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.