[PATCH] Critical ARC Fix for 3.12

[PATCH] Critical ARC Fix for 3.12

[Vineet Gupta]

Hi Linus,

Sorry for this extemely late patch for 3.12 but it causes a SMP build of ARC
to panic in boot.

Greg, the patch as it is doesn't apply to 3.10 (but does to 3.11). So can you
please queue it up for 3.11 and I'll send a fixup for 3.10.

Thx,
-Vineet


Vineet Gupta (1):
  ARC: Incorrect mm reference used in vmalloc fault handler

 arch/arc/mm/fault.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

-- 
1.8.1.2

[PATCH] ARC: Incorrect mm reference used in vmalloc fault handler

[Vineet Gupta]

A vmalloc fault needs to sync up PGD/PTE entry from init_mm to current task's
"active_mm". ARC vmalloc fault handler however was using mm.

A vmalloc fault for non user task context (actually pre-userland, from
init thread's open for /dev/console) caused the handler to deref NULL mm
(for mm->pgd)

The reasons it worked so far is amazing:

1. By default (!SMP), vmalloc fault handler uses a cached value of PGD.
   In SMP that MMU register is repurposed hence need for mm pointer deref.

2. In pre-3.12 SMP kernel, the problem triggering vmalloc didn't exist in
   pre-userland code path - it was introduced with commit 20bafb3d23d108bc
   "n_tty: Move buffers into n_tty_data"

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: Noam Camus <noamc@ezchip.com>
Cc: stable@vger.kernel.org    #3.10 and 3.11
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
---
 arch/arc/mm/fault.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 81554ded1260..9c69552350c4 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -17,7 +17,7 @@
 #include <asm/pgalloc.h>
 #include <asm/mmu.h>
 
-static int handle_vmalloc_fault(struct mm_struct *mm, unsigned long address)
+static int handle_vmalloc_fault(unsigned long address)
 {
 	/*
 	 * Synchronize this task's top level page-table
@@ -27,7 +27,7 @@ static int handle_vmalloc_fault(struct mm_struct *mm, unsigned long address)
 	pud_t *pud, *pud_k;
 	pmd_t *pmd, *pmd_k;
 
-	pgd = pgd_offset_fast(mm, address);
+	pgd = pgd_offset_fast(current->active_mm, address);
 	pgd_k = pgd_offset_k(address);
 
 	if (!pgd_present(*pgd_k))
@@ -72,7 +72,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	 * nothing more.
 	 */
 	if (address >= VMALLOC_START && address <= VMALLOC_END) {
-		ret = handle_vmalloc_fault(mm, address);
+		ret = handle_vmalloc_fault(address);
 		if (unlikely(ret))
 			goto bad_area_nosemaphore;
 		else
-- 
1.8.1.2

Re: [PATCH] Critical ARC Fix for 3.12

[Geert Uytterhoeven]

Added CC stable, so Greg will see it.
Added commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622, so Greg knows
what to cherry-pick.

On Sat, Nov 2, 2013 at 1:17 PM, Vineet Gupta <Vineet.Gupta1@synopsys.com> wrote:
> Hi Linus,
>
> Sorry for this extemely late patch for 3.12 but it causes a SMP build of ARC
> to panic in boot.
>
> Greg, the patch as it is doesn't apply to 3.10 (but does to 3.11). So can you
> please queue it up for 3.11 and I'll send a fixup for 3.10.
>
> Thx,
> -Vineet
>
>
> Vineet Gupta (1):
>   ARC: Incorrect mm reference used in vmalloc fault handler
>
>  arch/arc/mm/fault.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] Critical ARC Fix for 3.12

[Vineet Gupta]

On 11/03/2013 03:59 PM, Geert Uytterhoeven wrote:
> Added CC stable, so Greg will see it.
> Added commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622, so Greg knows
> what to cherry-pick.

Thanks Geert. While cover-letter was not, the patch itself was CC'ed to stable -
this cover letter, with PATCH prefix has caused enough confusion already :-(

Greg, I have verified that patch builds fine with 3.10 and 3.11. Please take it.

-Vineet

Re: [PATCH] Critical ARC Fix for 3.12

[Greg KH]

On Sun, Nov 03, 2013 at 11:29:54AM +0100, Geert Uytterhoeven wrote:
> Added CC stable, so Greg will see it.
> Added commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622, so Greg knows
> what to cherry-pick.

It was already tagged with a cc: stable marking, so all is good.

thanks,

greg k-h