Sebastian Andrzej Siewior
701e060705
After rt_mutex_wait_proxy_lock() task_struct::pi_blocked_on is cleared if current owns the lock. If the operation has been interrupted by a signal or timeout then pi_blocked_on can be set. This means spin_lock() *can* overwrite pi_blocked_on on PREEMPT_RT. This has been noticed by the recently added lockdep-asserts… The rt_mutex_cleanup_proxy_lock() operation will clear pi_blocked_on (and update pending waiters as expected) but it must happen under the hb lock to ensure the same state in rtmutex and userland. Given all the possibilities it is probably the simplest option to try-lock the hb lock. In case the lock is occupied a quick nap is needed. A busy loop can lock up the system if performed by a task with high priorioty preventing the owner from running. The rt_mutex_post_schedule() needs to be put before try-lock-loop because otherwie the schedule() in schedule_hrtimeout() will trip over the !sched_rt_mutex assert. Introduce futex_trylock_hblock() to try-lock the hb lock and sleep until the try-lock operation succeeds. Use it after rt_mutex_wait_proxy_lock() to acquire the lock. Suggested-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20230831095314.fTliy0Bh@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@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.