Revert "parisc: Re-enable interrupts early"

This reverts commit 5c38602d83e584047906b41b162ababd4db4106d.

Interrupts can't be enabled early because the register saves are done on
the thread stack prior to switching to the IRQ stack.  This caused stack
overflows and the thread stack needed increasing to 32k.  Even then,
stack overflows still occasionally occurred.

Background:
Even with a 32 kB thread stack, I have seen instances where the thread
stack overflowed on the mx3210 buildd.  Detection of stack overflow only
occurs when we have an external interrupt.  When an external interrupt
occurs, we switch to the thread stack if we are not already on a kernel
stack.  Then, registers and specials are saved to the kernel stack.

The bug occurs in intr_return where interrupts are reenabled prior to
returning from the interrupt.  This was done incase we need to schedule
or deliver signals.  However, it introduces the possibility that
multiple external interrupts may occur on the thread stack and cause a
stack overflow.  These might not be detected and cause the kernel to
misbehave in random ways.

This patch changes the code back to only reenable interrupts when we are
going to schedule or deliver signals.  As a result, we generally return
from an interrupt before reenabling interrupts.  This minimizes the
growth of the thread stack.

Fixes: 5c38602d83e5 ("parisc: Re-enable interrupts early")
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Cc: <stable@vger.kernel.org> # v4.10+
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index a4fd296c958e8e14f13a913aca50510b11eb49b7..f3cecf5117cf8ab14724f0ea3535220c3224d569 100644 (file)
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -878,9 +878,6 @@ ENTRY_CFI(syscall_exit_rfi)
        STREG   %r19,PT_SR7(%r16)
 
 intr_return:
-       /* NOTE: Need to enable interrupts incase we schedule. */
-       ssm     PSW_SM_I, %r0
-
        /* check for reschedule */
        mfctl   %cr30,%r1
        LDREG   TI_FLAGS(%r1),%r19      /* sched.h: TIF_NEED_RESCHED */
@@ -907,6 +904,11 @@ intr_check_sig:
        LDREG   PT_IASQ1(%r16), %r20
        cmpib,COND(=),n 0,%r20,intr_restore /* backward */
 
+       /* NOTE: We need to enable interrupts if we have to deliver
+        * signals. We used to do this earlier but it caused kernel
+        * stack overflows. */
+       ssm     PSW_SM_I, %r0
+
        copy    %r0, %r25                       /* long in_syscall = 0 */
 #ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29                  /* Reference param save area */
@@ -958,6 +960,10 @@ intr_do_resched:
        cmpib,COND(=)   0, %r20, intr_do_preempt
        nop
 
+       /* NOTE: We need to enable interrupts if we schedule.  We used
+        * to do this earlier but it caused kernel stack overflows. */
+       ssm     PSW_SM_I, %r0
+
 #ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29          /* Reference param save area */
 #endif