ChangeSet 1.2446, 2004/11/01 13:04:46-08:00, akpm@osdl.org [PATCH] Possible race in sysfs_read_file() and sysfs_write_file() 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 Signed-off-by: Greg Kroah-Hartman fs/sysfs/file.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletion(-) diff -Nru a/fs/sysfs/file.c b/fs/sysfs/file.c --- a/fs/sysfs/file.c 2004-11-01 13:36:42 -08:00 +++ b/fs/sysfs/file.c 2004-11-01 13:36:42 -08:00 @@ -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