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sched_ext dispatches tasks from the BPF scheduler from balance_scx() and thus every pick_task_scx() call must be preceded by balance_scx(). While this usually holds, due to a bug, there are cases where the fair class's balance() returns true indicating that it has tasks to run on the CPU and thus terminating balance() calls but fails to actually find the next task to run when pick_task() is called. In such cases, pick_task_scx() can be called without preceding balance_scx(). Detect this condition using SCX_RQ_BAL_PENDING flags. If detected, keep running the previous task if possible and avoid stalling from entering idle without balancing. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/Ztj_h5c2LYsdXYbA@slm.duckdns.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 reStructuredText 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.