proc: simpler iterations for /proc/*/cmdline

"rv" variable is used both as a counter of bytes transferred and an error
value holder but it can be reduced solely to error values if original
start of userspace buffer is stashed and used at the very end.

Link: http://lkml.kernel.org/r/20180221193009.GA28678@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

1 files changed, 17 insertions, 19 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6aa3fa538eaa..dc0829814253 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -238,8 +238,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 	unsigned long arg_start, arg_end, env_start, env_end;
 	unsigned long len1, len2, len;
 	unsigned long p;
+	char __user *buf0 = buf;
 	char c;
-	ssize_t rv;
+	int rv;
 
 	BUG_ON(*pos < 0);
 
@@ -269,25 +270,20 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 	len2 = env_end - env_start;
 
 	/* Empty ARGV. */
-	if (len1 == 0) {
-		rv = 0;
-		goto out_free_page;
-	}
+	if (len1 == 0)
+		goto end;
+
 	/*
 	 * Inherently racy -- command line shares address space
 	 * with code and data.
 	 */
-	if (access_remote_vm(mm, arg_end - 1, &c, 1, 0) != 1) {
-		rv = 0;
-		goto out_free_page;
-	}
-
-	rv = 0;
+	if (access_remote_vm(mm, arg_end - 1, &c, 1, 0) != 1)
+		goto end;
 
 	if (c == '\0') {
 		/* Command line (set of strings) occupies whole ARGV. */
 		if (len1 <= *pos)
-			goto out_free_page;
+			goto end;
 
 		p = arg_start + *pos;
 		len = len1 - *pos;
@@ -297,7 +293,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 			nr_read = min3(count, len, PAGE_SIZE);
 			nr_read = access_remote_vm(mm, p, page, nr_read, 0);
 			if (nr_read == 0)
-				goto out_free_page;
+				goto end;
 
 			if (copy_to_user(buf, page, nr_read)) {
 				rv = -EFAULT;
@@ -308,7 +304,6 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 			len	-= nr_read;
 			buf	+= nr_read;
 			count	-= nr_read;
-			rv	+= nr_read;
 		}
 	} else {
 		/*
@@ -339,7 +334,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 				nr_read = min3(count, len, PAGE_SIZE);
 				nr_read = access_remote_vm(mm, p, page, nr_read, 0);
 				if (nr_read == 0)
-					goto out_free_page;
+					goto end;
 
 				/*
 				 * Command line can be shorter than whole ARGV
@@ -356,10 +351,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 				len	-= nr_write;
 				buf	+= nr_write;
 				count	-= nr_write;
-				rv	+= nr_write;
 
 				if (nr_write < nr_read)
-					goto out_free_page;
+					goto end;
 			}
 
 			/* Only first chunk can be read partially. */
@@ -368,12 +362,16 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 		}
 	}
 
+end:
+	free_page((unsigned long)page);
+	mmput(mm);
+	*pos += buf - buf0;
+	return buf - buf0;
+
 out_free_page:
 	free_page((unsigned long)page);
 out_mmput:
 	mmput(mm);
-	if (rv > 0)
-		*pos += rv;
 	return rv;
 }