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ARM: uaccess: fix undefined instruction on ARMv7M/noMMU
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The use of get_domain() in copy_thread() results in an oops on
ARMv7M/noMMU systems.  The thread cpu_domain value is only used when
CONFIG_CPU_USE_DOMAINS is enabled, so there's no need to save the
value in copy_thread() except when this is enabled, and this option
will never be enabled on these platforms.

Unhandled exception: IPSR = 00000006 LR = fffffff1
CPU: 0 PID: 0 Comm: swapper Not tainted 4.2.0-next-20150909-00001-gb8ec5ad #41
Hardware name: NXP LPC18xx/43xx (Device Tree)
task: 2823fbe0 ti: 2823c000 task.ti: 2823c000
PC is at copy_thread+0x18/0x92
LR is at copy_thread+0x19/0x92
pc : [<2800a46e>]    lr : [<2800a46f>]    psr: 4100000b
sp : 2823df00  ip : 00000000  fp : 287c81c0
r10: 00000000  r9 : 00800300  r8 : 287c8000
r7 : 287c8000  r6 : 2818908d  r5 : 00000000  r4 : 287ca000
r3 : 00000000  r2 : 00000000  r1 : fffffff0  r0 : 287ca048
xPSR: 4100000b

Reported-by: Ariel D'Alessandro <ariel@vanguardiasur.com.ar>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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Russell King committed Sep 9, 2015
1 parent 296254f commit af4cb25
Showing 1 changed file with 2 additions and 0 deletions.
2 changes: 2 additions & 0 deletions arch/arm/kernel/process.c
Original file line number Diff line number Diff line change
Expand Up @@ -233,13 +233,15 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,

memset(&thread->cpu_context, 0, sizeof(struct cpu_context_save));

#ifdef CONFIG_CPU_USE_DOMAINS
/*
* Copy the initial value of the domain access control register
* from the current thread: thread->addr_limit will have been
* copied from the current thread via setup_thread_stack() in
* kernel/fork.c
*/
thread->cpu_domain = get_domain();
#endif

if (likely(!(p->flags & PF_KTHREAD))) {
*childregs = *current_pt_regs();
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