MIPS: Call find_vma with the mmap_sem held

Performing vma lookups without taking the mm->mmap_sem is asking
for trouble. While doing the search, the vma in question can be
modified or even removed before returning to the caller. Take the
lock (exclusively) in order to avoid races while iterating through
the vmacache and/or rbtree.

Updates two functions:
  - process_fpemu_return()
  - cteon_flush_cache_sigtramp()

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Tested-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Cc: akpm@linux-foundation.org
Cc: zeus@gnu.org
Cc: aswin@hp.com
Cc: davidlohr@hp.com
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Patchwork: http://patchwork.linux-mips.org/patch/6811/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 4 insertions, 0 deletions

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index 8119ac2fdfc9..d57fc10df773 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -712,10 +712,12 @@ int process_fpemu_return(int sig, void __user *fault_addr)
                 si.si_addr = fault_addr;
                 si.si_signo = sig;
                 if (sig == SIGSEGV) {
+                        down_read(&current->mm->mmap_sem);
                         if (find_vma(current->mm, (unsigned long)fault_addr))
                                 si.si_code = SEGV_ACCERR;
                         else
                                 si.si_code = SEGV_MAPERR;
+                        up_read(&current->mm->mmap_sem);
                 } else {
                         si.si_code = BUS_ADRERR;
                 }
diff --git a/arch/mips/mm/c-octeon.c b/arch/mips/mm/c-octeon.c
index f41a5c5b0865..05b1d7cf9514 100644
--- a/arch/mips/mm/c-octeon.c
+++ b/arch/mips/mm/c-octeon.c
@@ -137,8 +137,10 @@ static void octeon_flush_cache_sigtramp(unsigned long addr)
 {
         struct vm_area_struct *vma;
 
+        down_read(&current->mm->mmap_sem);
         vma = find_vma(current->mm, addr);
         octeon_flush_icache_all_cores(vma);
+        up_read(&current->mm->mmap_sem);
 }