9fa24404f5
powerpc/64 can boot on a non-zero SMP processor id. Initially, the boot CPU is said to be "assumed to be 0" until early_init_devtree() discovers the id from the device tree. That is not a good description because the assumption can be wrong and that has to be handled, the better description is that 0 is used as a placeholder, and things are fixed after the real id is discovered. smp_processor_id() is set to the boot cpuid, but task_cpu(current) is not, which causes the smp_processor_id() == task_cpu(current) invariant to be broken until init_idle() in sched_init(). This is quite fragile and could lead to subtle bugs in future. One bug is that validate_sp_size uses task_cpu() to get the process stack, so any stack trace from the booting CPU between early_init_devtree() and sched_init() will have problems. Early on paca_ptrs[0] will be poisoned, so that can cause machine checks dereferencing that memory in real mode. Later, validating the current stack pointer against the idle task of a different secondary will probably cause no stack trace to be printed. Fix this by setting thread_info->cpu right after smp_processor_id() is set to the boot cpuid. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> [mpe: Fix SMP=n build as reported by sfr] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221216115930.2667772-3-npiggin@gmail.com
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.