sh: Conditionally re-enable IRQs in fault path.

The current kernel behaviour is to reenable interrupts unconditionally
when taking a page fault. This patch changes this to only enable them
if interrupts were previously enabled.

It also fixes a problem seen with this fix in place: the kernel previously
flushed the vsyscall page when handling a signal, which is not only
unncessary, but caused a possible sleep with interrupts disabled.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/sh/mm/fault_32.c b/arch/sh/mm/fault_32.c
index d1fa27594c6e..0c776fdfbdda 100644
--- a/arch/sh/mm/fault_32.c
+++ b/arch/sh/mm/fault_32.c
@@ -37,16 +37,12 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
         int fault;
         siginfo_t info;
 
-        trace_hardirqs_on();
-        local_irq_enable();
-
 #ifdef CONFIG_SH_KGDB
         if (kgdb_nofault && kgdb_bus_err_hook)
                 kgdb_bus_err_hook();
 #endif
 
         tsk = current;
-        mm = tsk->mm;
         si_code = SEGV_MAPERR;
 
         if (unlikely(address >= TASK_SIZE)) {
@@ -88,6 +84,14 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
                 return;
         }
 
+        /* Only enable interrupts if they were on before the fault */
+        if ((regs->sr & SR_IMASK) != SR_IMASK) {
+                trace_hardirqs_on();
+                local_irq_enable();
+        }
+
+        mm = tsk->mm;
+
         /*
          * If we're in an interrupt or have no user
          * context, we must not take the fault..