ac0a36461f
has been pointing out constant problems. The changes have been going into the stack tracer, but it has been discovered that the problem isn't with the stack tracer itself, but it is with calling save_stack_trace() from within the internals of RCU. The stack tracer is the one that can trigger the issue the easiest, but examining the problem further, it could also happen from a WARN() in the wrong place, or even if an NMI happened in this area and it did an rcu_read_lock(). The critical area is where RCU is not watching. Which can happen while going to and from idle, or bringing up or taking down a CPU. The final fix was to put the protection in kernel_text_address() as it is the one that requires RCU to be watching while doing the stack trace. To make this work properly, Paul had to allow rcu_irq_enter() happen after rcu_nmi_enter(). This should have been done anyway, since an NMI can page fault (reading vmalloc area), and a page fault triggers rcu_irq_enter(). One patch is just a consolidation of code so that the fix only needed to be done in one location. -----BEGIN PGP SIGNATURE----- iQFIBAABCAAyFiEEQEw9Eu0DdyUUkuUUybkF8mrZjcsFAlnGyXoUHHJvc3RlZHRA Z29vZG1pcy5vcmcACgkQybkF8mrZjctKtwf8CeKGqOdlqkZEafIpWaIASXmAVMO/ WE+hQK+rCydWFvzADgb/rOmsR0ou8WGEXcuUPxVxmvMyqhKhZ6AU1hE/7Y8P0pMq F4bev+j3lAJC65ezFAh+ZQcIjaRIH4MFVPsUTaibSPSN7xziMNIpbf9VOVfpUm8A jf9p6YAmyhFVi6DstCc29SWnywEVwC2ZWRVKRPXKry8/dPxjfVcLclGX680Eqi9I EnYaOdC/mGbtvHPOUSs/P0cfxExHmyEErQHeOV8FPymj6KJ6+KoYIiELNlTHUBj/ eeKzrHc/b3j+lz0RPlA8WxYmpmEm4SE5cV3vRebdBNUBrABSN1RxeOozyQ== =1KkS -----END PGP SIGNATURE----- Merge tag 'trace-v4.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing fixes from Steven Rostedt: "Stack tracing and RCU has been having issues with each other and lockdep has been pointing out constant problems. The changes have been going into the stack tracer, but it has been discovered that the problem isn't with the stack tracer itself, but it is with calling save_stack_trace() from within the internals of RCU. The stack tracer is the one that can trigger the issue the easiest, but examining the problem further, it could also happen from a WARN() in the wrong place, or even if an NMI happened in this area and it did an rcu_read_lock(). The critical area is where RCU is not watching. Which can happen while going to and from idle, or bringing up or taking down a CPU. The final fix was to put the protection in kernel_text_address() as it is the one that requires RCU to be watching while doing the stack trace. To make this work properly, Paul had to allow rcu_irq_enter() happen after rcu_nmi_enter(). This should have been done anyway, since an NMI can page fault (reading vmalloc area), and a page fault triggers rcu_irq_enter(). One patch is just a consolidation of code so that the fix only needed to be done in one location" * tag 'trace-v4.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: tracing: Remove RCU work arounds from stack tracer extable: Enable RCU if it is not watching in kernel_text_address() extable: Consolidate *kernel_text_address() functions rcu: Allow for page faults in NMI handlers |
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README
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.