ext4: fix races in ext4_sync_parent()
Fix problems if fsync() races against a rename of a parent directory
as pointed out by Al Viro in his own inimitable way:
>While we are at it, could somebody please explain what the hell is ext4
>doing in
>static int ext4_sync_parent(struct inode *inode)
>{
> struct writeback_control wbc;
> struct dentry *dentry = NULL;
> int ret = 0;
>
> while (inode && ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
> ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
> dentry = list_entry(inode->i_dentry.next,
> struct dentry, d_alias);
> if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode)
> break;
> inode = dentry->d_parent->d_inode;
> ret = sync_mapping_buffers(inode->i_mapping);
> ...
>Note that dentry obviously can't be NULL there. dentry->d_parent is never
>NULL. And dentry->d_parent would better not be negative, for crying out
>loud! What's worse, there's no guarantees that dentry->d_parent will
>remain our parent over that sync_mapping_buffers() *and* that inode won't
>just be freed under us (after rename() and memory pressure leading to
>eviction of what used to be our dentry->d_parent)......
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index ce66d2f..f9dbe33 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -129,15 +129,30 @@
{
struct writeback_control wbc;
struct dentry *dentry = NULL;
+ struct inode *next;
int ret = 0;
- while (inode && ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
+ if (!ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY))
+ return 0;
+ inode = igrab(inode);
+ while (ext4_test_inode_state(inode, EXT4_STATE_NEWENTRY)) {
ext4_clear_inode_state(inode, EXT4_STATE_NEWENTRY);
- dentry = list_entry(inode->i_dentry.next,
- struct dentry, d_alias);
- if (!dentry || !dentry->d_parent || !dentry->d_parent->d_inode)
+ dentry = NULL;
+ spin_lock(&inode->i_lock);
+ if (!list_empty(&inode->i_dentry)) {
+ dentry = list_first_entry(&inode->i_dentry,
+ struct dentry, d_alias);
+ dget(dentry);
+ }
+ spin_unlock(&inode->i_lock);
+ if (!dentry)
break;
- inode = dentry->d_parent->d_inode;
+ next = igrab(dentry->d_parent->d_inode);
+ dput(dentry);
+ if (!next)
+ break;
+ iput(inode);
+ inode = next;
ret = sync_mapping_buffers(inode->i_mapping);
if (ret)
break;
@@ -148,6 +163,7 @@
if (ret)
break;
}
+ iput(inode);
return ret;
}