This is a note to let you know that I've just added the patch titled

Revert "parisc: Re-enable interrupts early"

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: revert-parisc-re-enable-interrupts-early.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 9352aeada4d8d8753fc0e414fbfe8fdfcb68a12c Mon Sep 17 00:00:00 2001

From: John David Anglin dave.anglin@bell.net Date: Mon, 13 Nov 2017 19:35:33 -0500 Subject: Revert "parisc: Re-enable interrupts early"

From: John David Anglin dave.anglin@bell.net

commit 9352aeada4d8d8753fc0e414fbfe8fdfcb68a12c upstream.

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 Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/parisc/kernel/entry.S | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)

--- 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

Patches currently in stable-queue which might be from dave.anglin@bell.net are

queue-4.14/revert-parisc-re-enable-interrupts-early.patch