[PATCH] sysfs: reinstate exclusion between method calls and attribute unregistration

Alan Stern
2007-03-15T19:51:30Z

This patch (as869) reinstates the mutual exclusion between sysfs
attribute method calls and attribute unregistration. The
previously-reported deadlocks have been fixed, and this exclusion is
by far the simplest way to avoid races during driver unbinding.

The check for orphaned read-buffers has been moved down slightly, so
that the remainder of a partially-read buffer will still be available
to userspace even after the attribute has been unregistered.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

---

Index: 2.6.21-rc3-git9/fs/sysfs/inode.c
===================================================================
--- 2.6.21-rc3-git9.orig/fs/sysfs/inode.c
+++ 2.6.21-rc3-git9/fs/sysfs/inode.c
@@ -222,13 +222,17 @@ const unsigned char * sysfs_get_name(str

static inline void orphan_all_buffers(struct inode *node)
{
- struct sysfs_buffer_collection *set = node->i_private;
+ struct sysfs_buffer_collection *set;
struct sysfs_buffer *buf;

mutex_lock_nested(&node->i_mutex, I_MUTEX_CHILD);
- if (node->i_private) {
- list_for_each_entry(buf, &set->associates, associates)
+ set = node->i_private;
+ if (set) {
+ list_for_each_entry(buf, &set->associates, associates) {
+ down(&buf->sem);
buf->orphaned = 1;
+ up(&buf->sem);
+ }
}
mutex_unlock(&node->i_mutex);
}
Index: 2.6.21-rc3-git9/fs/sysfs/file.c
===================================================================
--- 2.6.21-rc3-git9.orig/fs/sysfs/file.c
+++ 2.6.21-rc3-git9/fs/sysfs/file.c
@@ -168,12 +168,12 @@ sysfs_read_file(struct file *file, char
ssize_t retval = 0;

down(&buffer->sem);
- if (buffer->orphaned) {
- retval = -ENODEV;
- goto out;
- }
if (buffer->needs_read_fill) {
- if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
+ if (buffer->orphaned)
+ retval = -ENODEV;
+ else
+ retval = fill_read_buffer(file->f_path.dentry,buffer);
+ if (retval)
goto out;
}
pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",