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The below backtrace can be observed on -rt kernel with CONFIG_DEBUG_MODULE_RONX (4.9 kernel CONFIG_DEBUG_RODATA) option enabled: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:993 in_atomic(): 1, irqs_disabled(): 128, pid: 14, name: migration/0 1 lock held by migration/0/14: #0: (tasklist_lock){+.+...}, at: [<c01183e8>] update_sections_early+0x24/0xdc irq event stamp: 38 hardirqs last enabled at (37): [<c08f6f7c>] _raw_spin_unlock_irq+0x24/0x68 hardirqs last disabled at (38): [<c01fdfe8>] multi_cpu_stop+0xd8/0x138 softirqs last enabled at (0): [<c01303ec>] copy_process.part.5+0x238/0x1b64 softirqs last disabled at (0): [< (null)>] (null) Preemption disabled at: [<c01fe244>] cpu_stopper_thread+0x80/0x10c CPU: 0 PID: 14 Comm: migration/0 Not tainted 4.9.21-rt16-02220-g49e319c #15 Hardware name: Generic DRA74X (Flattened Device Tree) [<c0112014>] (unwind_backtrace) from [<c010d370>] (show_stack+0x10/0x14) [<c010d370>] (show_stack) from [<c049beb8>] (dump_stack+0xa8/0xd4) [<c049beb8>] (dump_stack) from [<c01631a0>] (___might_sleep+0x1bc/0x2ac) [<c01631a0>] (___might_sleep) from [<c08f7244>] (__rt_spin_lock+0x1c/0x30) [<c08f7244>] (__rt_spin_lock) from [<c08f77a4>] (rt_read_lock+0x54/0x68) [<c08f77a4>] (rt_read_lock) from [<c01183e8>] (update_sections_early+0x24/0xdc) [<c01183e8>] (update_sections_early) from [<c01184b0>] (__fix_kernmem_perms+0x10/0x1c) [<c01184b0>] (__fix_kernmem_perms) from [<c01fe010>] (multi_cpu_stop+0x100/0x138) [<c01fe010>] (multi_cpu_stop) from [<c01fe24c>] (cpu_stopper_thread+0x88/0x10c) [<c01fe24c>] (cpu_stopper_thread) from [<c015edc4>] (smpboot_thread_fn+0x174/0x31c) [<c015edc4>] (smpboot_thread_fn) from [<c015a988>] (kthread+0xf0/0x108) [<c015a988>] (kthread) from [<c0108818>] (ret_from_fork+0x14/0x3c) Freeing unused kernel memory: 1024K (c0d00000 - c0e00000) The stop_machine() is called with cpus = NULL from fix_kernmem_perms() and mark_rodata_ro() which means only one CPU will execute update_sections_early() while all other CPUs will spin and wait. Hence, it's safe to remove tasklist locking from update_sections_early(). As part of this change also mark functions which are local to this module as static. Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com> Acked-by: Laura Abbott <labbott@redhat.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
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.