linux-kernel - [PATCH] /dev/zero: Avoid repeated access

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Date:	Tue, 7 Jul 2009 10:59:19 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] /dev/zero: Avoid repeated access_ok() checks

In read_zero, we check for access_ok() once for the count bytes. It is
unnecessarily checked again in clear_user. Use __clear_user, which does not
check for access_ok().

Signed-off-by: Nikanth Karthikesan <knikanth@...e.de>

---
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index afa8813..3e05b48 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -690,7 +690,7 @@ static ssize_t read_zero(struct file * file, char __user * buf,
 
 		if (chunk > PAGE_SIZE)
 			chunk = PAGE_SIZE;	/* Just for latency reasons */
-		unwritten = clear_user(buf, chunk);
+		unwritten = __clear_user(buf, chunk);
 		written += chunk - unwritten;
 		if (unwritten)
 			break;

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