[PATCH 1/6] ARM: ensure interrupts are enabled in __do_user_fault()

[Russell King (Oracle)]

__do_user_fault() may be called from fault handling paths where the
interrupts are enabled or disabled. E.g. do_page_fault() calls this
with interrupts enabled, whereas do_sect_fault()->do_bad_area()
will call this with interrupts disabled. Since this is a userspace
fault, we know that interrupts were enabled in the parent context,
so call local_irq_enable() here to give a consistent interrupt state.

This is necessary for force_sig_info() when PREEMPT_RT is enabled.

Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
---
 arch/arm/mm/fault.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index ed4330cc3f4e..6c27ebd49093 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -190,7 +190,8 @@ __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
 
 /*
  * Something tried to access memory that isn't in our memory map..
- * User mode accesses just cause a SIGSEGV
+ * User mode accesses just cause a SIGSEGV. Ensure interrupts are enabled
+ * for preempt RT.
  */
 static void
 __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
@@ -198,6 +199,8 @@ __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
 {
 	struct task_struct *tsk = current;
 
+	local_irq_enable();
+
 #ifdef CONFIG_DEBUG_USER
 	if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
 	    ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
@@ -268,6 +271,7 @@ do_kernel_address_page_fault(struct mm_struct *mm, unsigned long addr,
 		 * should not be faulting in kernel space, which includes the
 		 * vector/khelper page. Handle the branch predictor hardening
 		 * while interrupts are still disabled, then send a SIGSEGV.
+		 * Note that __do_user_fault() will enable interrupts.
 		 */
 		harden_branch_predictor();
 		__do_user_fault(addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
-- 
2.47.3