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>