ARC: Incorrect mm reference used in vmalloc fault handler

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index d63f3de..0c14d8a 100644 (file)
--- 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(struct pt_regs *regs, unsigned long address)
         * 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