From: Simon Derr <Simon.Derr@bull.net>
- fixes the race between threads by adding a semaphore in sysfs_buffer
- allocates the buffer upon call to pread(). We still call again
fill_read_buffer() if the file is "rewinded" to offset zero.
- fixes the comparison in flush_read_buffer().
Signed-off-by: Simon Derr <simon.derr@null.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/sysfs/file.c | 18 +++++++++++++++---
1 files changed, 15 insertions(+), 3 deletions(-)
diff -puN fs/sysfs/file.c~fix-race-in-sysfs_read_file-and-sysfs_write_file fs/sysfs/file.c
--- 25/fs/sysfs/file.c~fix-race-in-sysfs_read_file-and-sysfs_write_file 2004-09-02 15:56:36.397176120 -0700
+++ 25-akpm/fs/sysfs/file.c 2004-09-02 15:56:36.402175360 -0700
@@ -6,6 +6,7 @@
#include <linux/dnotify.h>
#include <linux/kobject.h>
#include <asm/uaccess.h>
+#include <asm/semaphore.h>
#include "sysfs.h"
@@ -53,6 +54,7 @@ struct sysfs_buffer {
loff_t pos;
char * page;
struct sysfs_ops * ops;
+ struct semaphore sem;
};
@@ -106,6 +108,9 @@ static int flush_read_buffer(struct sysf
{
int error;
+ if (*ppos > buffer->count)
+ return 0;
+
if (count > (buffer->count - *ppos))
count = buffer->count - *ppos;
@@ -140,13 +145,17 @@ sysfs_read_file(struct file *file, char
struct sysfs_buffer * buffer = file->private_data;
ssize_t retval = 0;
- if (!*ppos) {
+ down(&buffer->sem);
+ if ((!*ppos) || (!buffer->page)) {
if ((retval = fill_read_buffer(file->f_dentry,buffer)))
- return retval;
+ goto out;
}
pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
__FUNCTION__,count,*ppos,buffer->page);
- return flush_read_buffer(buffer,buf,count,ppos);
+ retval = flush_read_buffer(buffer,buf,count,ppos);
+out:
+ up(&buffer->sem);
+ return retval;
}
@@ -220,11 +229,13 @@ sysfs_write_file(struct file *file, cons
{
struct sysfs_buffer * buffer = file->private_data;
+ down(&buffer->sem);
count = fill_write_buffer(buffer,buf,count);
if (count > 0)
count = flush_write_buffer(file->f_dentry,buffer,count);
if (count > 0)
*ppos += count;
+ up(&buffer->sem);
return count;
}
@@ -287,6 +298,7 @@ static int check_perm(struct inode * ino
buffer = kmalloc(sizeof(struct sysfs_buffer),GFP_KERNEL);
if (buffer) {
memset(buffer,0,sizeof(struct sysfs_buffer));
+ init_MUTEX(&buffer->sem);
buffer->ops = ops;
file->private_data = buffer;
} else
_