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2d1e38f566
Converting the cpu hotplug locking to a percpu rwsem unearthed hidden lock ordering problems. There is a wide range of locks involved in this: kprobe_mutex, jump_label_mutex, ftrace_lock, text_mutex, event_mutex, module_mutex, func_hash->regex_lock and a gazillion of lock order permutations with nested get_online_cpus() calls. Some of those permutations are potential deadlocks even with the current nesting hotplug locking scheme, but they can't be discovered by lockdep. The conversion of the hotplug locking to a percpu rwsem requires to prevent nested locking, so it's required to take the hotplug rwsem early in the call chain and establish a proper lock order. After quite some analysis and going down the wrong road severa times the following lock order has been chosen: kprobe_mutex -> cpus_rwsem -> jump_label_mutex -> text_mutex For kprobes which hook on an ftrace function trace point, it's required to drop cpus_rwsem before calling into the ftrace code to avoid a deadlock on the func_hash->regex_lock. [ Steven: Ftrace interaction fixes ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Ingo Molnar <mingo@kernel.org> Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Siewior <bigeasy@linutronix.de> Link: http://lkml.kernel.org/r/20170524081549.104864779@linutronix.de |
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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.