linux-kernel - [PATCH] arch/cris: use get_user_pages

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Date:   Sun, 21 Jan 2018 14:59:29 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     starvik@...s.com, jesper.nilsson@...s.com,
        akpm@...ux-foundation.org
Cc:     viro@...iv.linux.org.uk, linux-cris-kernel@...s.com,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] arch/cris: use get_user_pages_fast()

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 <dbueso@...e.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