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

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>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 8 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 1bafdf6e171c..fc4633378dc0 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -168,12 +168,12 @@ sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
         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",
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index ccb7d722c558..4de5c6b89918 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -222,13 +222,17 @@ const unsigned char * sysfs_get_name(struct sysfs_dirent *sd)
 
 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);
 }