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[ Upstream commit64ea6e44f8] Writing the current state back in hotplug/target calls cpu_down() which will set cpu dying even when it isn't and then nothing will ever clear it. A stress test that reads values and writes them back for all cpu device files in sysfs will trigger the BUG() in select_fallback_rq once all cpus are marked as dying. kernel/cpu.c::target_store() ... if (st->state < target) ret = cpu_up(dev->id, target); else ret = cpu_down(dev->id, target); cpu_down() -> cpu_set_state() bool bringup = st->state < target; ... if (cpu_dying(cpu) != !bringup) set_cpu_dying(cpu, !bringup); Fix this by letting state==target fall through in the target_store() conditional. Also make sure st->target == target in that case. Fixes:757c989b99("cpu/hotplug: Make target state writeable") Signed-off-by: Phil Auld <pauld@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Link: https://lore.kernel.org/r/20221117162329.3164999-2-pauld@redhat.com Signed-off-by: Sasha Levin <sashal@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 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.