From: Simon Derr Add a `needs_read_fill' field in sysfs_buffer so that reading after a write in a sysfs file returns valid data. (instead of the data that have been written, that may be invalid or at the wrong offset) Signed-off-by: Simon Derr Signed-off-by: Andrew Morton --- 25-akpm/fs/sysfs/file.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletion(-) diff -puN fs/sysfs/file.c~possible-race-in-sysfs_read_file-and-sysfs_write_file-update fs/sysfs/file.c --- 25/fs/sysfs/file.c~possible-race-in-sysfs_read_file-and-sysfs_write_file-update 2004-10-18 21:43:23.579081336 -0700 +++ 25-akpm/fs/sysfs/file.c 2004-10-18 21:43:23.583080728 -0700 @@ -55,6 +55,7 @@ struct sysfs_buffer { char * page; struct sysfs_ops * ops; struct semaphore sem; + int needs_read_fill; }; @@ -82,6 +83,7 @@ static int fill_read_buffer(struct dentr 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 @@ sysfs_read_file(struct file *file, char 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 @@ fill_write_buffer(struct sysfs_buffer * 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 @@ static int check_perm(struct inode * ino 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 _