Re: [PATCH] Possible race in sysfs_read_file() and sysfs_write_file()

[Simon Derr]

On Fri, 3 Sep 2004, Simon Derr wrote:

> Possible fix would be to add a 'dirty' flag to the sysfs_buffer when
> write() is called, so we force a call to fill_read_buffer() on the next
> read().

This additional patch does just that.
I'm just afraid the flag has not a very good name.

Signed-off-by: Simon Derr <simon.derr@xxxxxxxx>


Index: 269mm2kdb/fs/sysfs/file.c
===================================================================
--- 269mm2kdb.orig/fs/sysfs/file.c	2004-09-03 11:43:01.744675609 +0200
+++ 269mm2kdb/fs/sysfs/file.c	2004-09-03 11:56:06.993689427 +0200
@@ -55,6 +55,7 @@
 	char			* page;
 	struct sysfs_ops	* ops;
 	struct semaphore	sem;
+	int			needs_read_fill;
 };


@@ -82,6 +83,7 @@
 		return -ENOMEM;

 	count = ops->show(kobj,attr,buffer->page);
+	buffer->needs_read_fill = 0;
 	BUG_ON(count > (ssize_t)PAGE_SIZE);
 	if (count >= 0)
 		buffer->count = count;
@@ -146,7 +148,7 @@
 	ssize_t retval = 0;

 	down(&buffer->sem);
-	if ((!*ppos) || (!buffer->page)) {
+	if (buffer->needs_read_fill) {
 		if ((retval = fill_read_buffer(file->f_dentry,buffer)))
 			goto out;
 	}
@@ -182,6 +184,7 @@
 	if (count >= PAGE_SIZE)
 		count = PAGE_SIZE - 1;
 	error = copy_from_user(buffer->page,buf,count);
+	buffer->needs_read_fill = 1;
 	return error ? -EFAULT : count;
 }

@@ -299,6 +302,7 @@
 	if (buffer) {
 		memset(buffer,0,sizeof(struct sysfs_buffer));
 		init_MUTEX(&buffer->sem);
+		buffer->needs_read_fill = 1;
 		buffer->ops = ops;
 		file->private_data = buffer;
 	} else
-
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