From 949854d02455080d20cd3e1db28a3a18daf7599d Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:37 +1100 Subject: fs: Use rename lock and RCU for multi-step operations The remaining usages for dcache_lock is to allow atomic, multi-step read-side operations over the directory tree by excluding modifications to the tree. Also, to walk in the leaf->root direction in the tree where we don't have a natural d_lock ordering. This could be accomplished by taking every d_lock, but this would mean a huge number of locks and actually gets very tricky. Solve this instead by using the rename seqlock for multi-step read-side operations, retry in case of a rename so we don't walk up the wrong parent. Concurrent dentry insertions are not serialised against. Concurrent deletes are tricky when walking up the directory: our parent might have been deleted when dropping locks so also need to check and retry for that. We can also use the rename lock in cases where livelock is a worry (and it is introduced in subsequent patch). Signed-off-by: Nick Piggin --- drivers/staging/pohmelfs/path_entry.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) (limited to 'drivers/staging/pohmelfs') diff --git a/drivers/staging/pohmelfs/path_entry.c b/drivers/staging/pohmelfs/path_entry.c index 8ec83d2dffb7..bbe42f42ca8f 100644 --- a/drivers/staging/pohmelfs/path_entry.c +++ b/drivers/staging/pohmelfs/path_entry.c @@ -83,10 +83,11 @@ out: int pohmelfs_path_length(struct pohmelfs_inode *pi) { struct dentry *d, *root, *first; - int len = 1; /* Root slash */ + int len; + unsigned seq; - first = d = d_find_alias(&pi->vfs_inode); - if (!d) { + first = d_find_alias(&pi->vfs_inode); + if (!first) { dprintk("%s: ino: %llu, mode: %o.\n", __func__, pi->ino, pi->vfs_inode.i_mode); return -ENOENT; } @@ -95,6 +96,11 @@ int pohmelfs_path_length(struct pohmelfs_inode *pi) root = dget(current->fs->root.dentry); spin_unlock(¤t->fs->lock); +rename_retry: + len = 1; /* Root slash */ + d = first; + seq = read_seqbegin(&rename_lock); + rcu_read_lock(); spin_lock(&dcache_lock); if (!IS_ROOT(d) && d_unhashed(d)) @@ -105,6 +111,9 @@ int pohmelfs_path_length(struct pohmelfs_inode *pi) d = d->d_parent; } spin_unlock(&dcache_lock); + rcu_read_unlock(); + if (read_seqretry(&rename_lock, seq)) + goto rename_retry; dput(root); dput(first); -- cgit v1.2.3-55-g7522