[PATCH] arch/cris: use get_user_pages_fast()

[Davidlohr Bueso]

Since we currently hold mmap_sem across both gup calls (and
nothing more), we can substitute it with two _fast()
alternatives and possibly avoid grabbing the lock.

This was found while adding mmap_sem wrappers, and was also
previously reported by Al: https://lkml.org/lkml/2017/11/17/777

Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
---
 arch/cris/arch-v32/drivers/cryptocop.c | 29 ++++++++++-------------------
 1 file changed, 10 insertions(+), 19 deletions(-)

diff --git a/arch/cris/arch-v32/drivers/cryptocop.c 
b/arch/cris/arch-v32/drivers/cryptocop.c
index d688fe117dca..76f8d3b1d39e 100644
--- a/arch/cris/arch-v32/drivers/cryptocop.c
+++ b/arch/cris/arch-v32/drivers/cryptocop.c
@@ -2717,37 +2717,28 @@ static int cryptocop_ioctl_process(struct inode *inode, 
struct file *filp, unsig
                }
        }
 
-       /* Acquire the mm page semaphore. */
-       down_read(&current->mm->mmap_sem);
-
-       err = get_user_pages((unsigned long int)(oper.indata + prev_ix),
-                            noinpages,
-                            0,  /* read access only for in data */
-                            inpages,
-                            NULL);
+       err = get_user_pages_fast((unsigned long int)(oper.indata + prev_ix),
+                                 noinpages,
+                                 0,  /* read access only for in data */
+                                 inpages);
 
        if (err < 0) {
-               up_read(&current->mm->mmap_sem);
                nooutpages = noinpages = 0;
-               DEBUG_API(printk("cryptocop_ioctl_process: get_user_pages 
indata\n"));
+               DEBUG_API(printk("cryptocop_ioctl_process: get_user_pages_fast 
indata\n"));
                goto error_cleanup;
        }
        noinpages = err;
        if (oper.do_cipher){
-               err = get_user_pages((unsigned long int)oper.cipher_outdata,
-                                    nooutpages,
-                                    FOLL_WRITE, /* write access for out data */
-                                    outpages,
-                                    NULL);
-               up_read(&current->mm->mmap_sem);
+               err = get_user_pages_fast((unsigned long 
int)oper.cipher_outdata,
+                                         nooutpages,
+                                         FOLL_WRITE, /* write access for out 
data */
+                                         outpages);
                if (err < 0) {
                        nooutpages = 0;
-                       DEBUG_API(printk("cryptocop_ioctl_process: 
get_user_pages outdata\n"));
+                       DEBUG_API(printk("cryptocop_ioctl_process: 
get_user_pages_fast outdata\n"));
                        goto error_cleanup;
                }
                nooutpages = err;
-       } else {
-               up_read(&current->mm->mmap_sem);
        }
 
        /* Add 6 to nooutpages to make room for possibly inserted buffers for 
storing digest and
-- 
2.13.6