From: Alan Stern <stern@rowland.harvard.edu>
Date: Thu, 15 Mar 2007 19:51:28 +0000 (-0400)
Subject: [PATCH] sysfs: reinstate exclusion between method calls and attribute unregistration
X-Git-Tag: v2.6.21-rc4~2
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=e7b0d26a86943370c04d6833c6edba2a72a6e240;p=linux-2.6-omap-h63xx.git

[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>
---

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 1bafdf6e171..fc4633378dc 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 ccb7d722c55..4de5c6b8991 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);
 }