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scx_ops_init_task() and the follow-up scx_ops_enable_task() in the fork path were gated by scx_enabled() test and thus __scx_ops_enabled had to be turned on before the first scx_ops_init_task() loop in scx_ops_enable(). However, if an external entity causes sched_class switch before the loop is complete, tasks which are not initialized could be switched to SCX. The following can be reproduced by running a program which keeps toggling a process between SCHED_OTHER and SCHED_EXT using sched_setscheduler(2). sched_ext: Invalid task state transition 0 -> 3 for fish[1623] WARNING: CPU: 1 PID: 1650 at kernel/sched/ext.c:3392 scx_ops_enable_task+0x1a1/0x200 ... Sched_ext: simple (enabling) RIP: 0010:scx_ops_enable_task+0x1a1/0x200 ... switching_to_scx+0x13/0xa0 __sched_setscheduler+0x850/0xa50 do_sched_setscheduler+0x104/0x1c0 __x64_sys_sched_setscheduler+0x18/0x30 do_syscall_64+0x7b/0x140 entry_SYSCALL_64_after_hwframe+0x76/0x7e Fix it by gating scx_ops_init_task() separately using scx_ops_init_task_enabled. __scx_ops_enabled is now set after all tasks are finished with scx_ops_init_task(). Signed-off-by: Tejun Heo <tj@kernel.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.