Commit 9c41f4ee authored by Vineet Gupta's avatar Vineet Gupta Committed by Linus Torvalds
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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 20bafb3d

   "n_tty: Move buffers into n_tty_data"
Signed-off-by: default avatarVineet Gupta <>
Cc: Gilad Ben-Yossef <>
Cc: Noam Camus <>
Cc:    #3.10 and 3.11
Cc: Peter Hurley <>
Signed-off-by: default avatarLinus Torvalds <>
parent 9581b7d2
......@@ -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;
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