From 7b1a14bbb0e547aaa4d30cc376e6c8c12539ab0f Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Mon, 27 Apr 2009 10:49:53 -0400 Subject: Btrfs: fix acl caching Linus noticed the btrfs code to cache acls wasn't properly caching a NULL acl when the inode didn't have any acls. This meant the common case of no acls resulted in expensive btree searches every time the kernel checked permissions (which is quite often). This is a modified version of Linus' original patch: Properly set initial acl fields to BTRFS_ACL_NOT_CACHED in the inode. This forces an acl lookup when permission checks are done. Fix btrfs_get_acl to avoid lookups and locking when the inode acls fields are set to null. Fix btrfs_get_acl to use the right return value from __btrfs_getxattr when deciding to cache a NULL acl. It was storing a NULL acl when __btrfs_getxattr return -ENOENT, but __btrfs_getxattr was actually returning -ENODATA for this case. Signed-off-by: Chris Mason --- fs/btrfs/acl.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'fs/btrfs/acl.c') diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c index 7fdd184a528..cbba000dccb 100644 --- a/fs/btrfs/acl.c +++ b/fs/btrfs/acl.c @@ -60,15 +60,20 @@ static struct posix_acl *btrfs_get_acl(struct inode *inode, int type) return ERR_PTR(-EINVAL); } + /* Handle the cached NULL acl case without locking */ + acl = ACCESS_ONCE(*p_acl); + if (!acl) + return acl; + spin_lock(&inode->i_lock); - if (*p_acl != BTRFS_ACL_NOT_CACHED) - acl = posix_acl_dup(*p_acl); + acl = *p_acl; + if (acl != BTRFS_ACL_NOT_CACHED) + acl = posix_acl_dup(acl); spin_unlock(&inode->i_lock); - if (acl) + if (acl != BTRFS_ACL_NOT_CACHED) return acl; - size = __btrfs_getxattr(inode, name, "", 0); if (size > 0) { value = kzalloc(size, GFP_NOFS); @@ -80,9 +85,12 @@ static struct posix_acl *btrfs_get_acl(struct inode *inode, int type) btrfs_update_cached_acl(inode, p_acl, acl); } kfree(value); - } else if (size == -ENOENT) { + } else if (size == -ENOENT || size == -ENODATA || size == 0) { + /* FIXME, who returns -ENOENT? I think nobody */ acl = NULL; btrfs_update_cached_acl(inode, p_acl, acl); + } else { + acl = ERR_PTR(-EIO); } return acl; -- cgit v1.2.3-70-g09d2