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A hang on CPU0 onlining after a preceding offlining is observed. Trace shows that CPU0 is stuck in check_tsc_sync_target() waiting for source CPU to run check_tsc_sync_source() but this never happens. Source CPU, in its turn, is stuck on synchronize_sched() which is called from native_cpu_up() -> do_boot_cpu() -> unregister_nmi_handler(). So it's a classic ABBA deadlock, due to the use of synchronize_sched() in unregister_nmi_handler(). Fix the bug by moving unregister_nmi_handler() from do_boot_cpu() to native_cpu_up() after cpu onlining is done. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170803105818.9934-1-vkuznets@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.