3.11-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx>
commit 9c41f4eeb9d51f3ece20428d35a3ea32cf3b5622 upstream.
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@xxxxxxxxxxxx>
Cc: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
Cc: Noam Camus <noamc@xxxxxxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arc/mm/fault.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- 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 m
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))
@@ -73,7 +73,7 @@ void do_page_fault(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
--
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