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authorDavid Howells <dhowells@redhat.com>2020-04-10 15:23:27 +0100
committerDavid Howells <dhowells@redhat.com>2020-04-13 15:09:01 +0100
commit2105c2820d366b76f38e6ad61c75771881ecc532 (patch)
tree844875c0e41ad206541baa3b44bc77ba89d78ba2 /fs/afs/dir_silly.c
parent3efe55b09a92a59ed8214db801683cf13c9742c4 (diff)
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afs: Fix race between post-modification dir edit and readdir/d_revalidate
AFS directories are retained locally as a structured file, with lookup being effected by a local search of the file contents. When a modification (such as mkdir) happens, the dir file content is modified locally rather than redownloading the directory. The directory contents are accessed in a number of ways, with a number of different locks schemes: (1) Download of contents - dvnode->validate_lock/write in afs_read_dir(). (2) Lookup and readdir - dvnode->validate_lock/read in afs_dir_iterate(), downgrading from (1) if necessary. (3) d_revalidate of child dentry - dvnode->validate_lock/read in afs_do_lookup_one() downgrading from (1) if necessary. (4) Edit of dir after modification - page locks on individual dir pages. Unfortunately, because (4) uses different locking scheme to (1) - (3), nothing protects against the page being scanned whilst the edit is underway. Even download is not safe as it doesn't lock the pages - relying instead on the validate_lock to serialise as a whole (the theory being that directory contents are treated as a block and always downloaded as a block). Fix this by write-locking dvnode->validate_lock around the edits. Care must be taken in the rename case as there may be two different dirs - but they need not be locked at the same time. In any case, once the lock is taken, the directory version must be rechecked, and the edit skipped if a later version has been downloaded by revalidation (there can't have been any local changes because the VFS holds the inode lock, but there can have been remote changes). Fixes: 63a4681ff39c ("afs: Locally edit directory data for mkdir/create/unlink/...") Signed-off-by: David Howells <dhowells@redhat.com>
Diffstat (limited to 'fs/afs/dir_silly.c')
-rw-r--r--fs/afs/dir_silly.c22
1 files changed, 15 insertions, 7 deletions
diff --git a/fs/afs/dir_silly.c b/fs/afs/dir_silly.c
index 361088a5edb9..d94e2b7cddff 100644
--- a/fs/afs/dir_silly.c
+++ b/fs/afs/dir_silly.c
@@ -21,6 +21,7 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode
{
struct afs_fs_cursor fc;
struct afs_status_cb *scb;
+ afs_dataversion_t dir_data_version;
int ret = -ERESTARTSYS;
_enter("%pd,%pd", old, new);
@@ -31,7 +32,7 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode
trace_afs_silly_rename(vnode, false);
if (afs_begin_vnode_operation(&fc, dvnode, key, true)) {
- afs_dataversion_t dir_data_version = dvnode->status.data_version + 1;
+ dir_data_version = dvnode->status.data_version + 1;
while (afs_select_fileserver(&fc)) {
fc.cb_break = afs_calc_vnode_cb_break(dvnode);
@@ -54,12 +55,15 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode
dvnode->silly_key = key_get(key);
}
- if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
+ down_write(&dvnode->validate_lock);
+ if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags) &&
+ dvnode->status.data_version == dir_data_version) {
afs_edit_dir_remove(dvnode, &old->d_name,
afs_edit_dir_for_silly_0);
- if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
afs_edit_dir_add(dvnode, &new->d_name,
&vnode->fid, afs_edit_dir_for_silly_1);
+ }
+ up_write(&dvnode->validate_lock);
}
kfree(scb);
@@ -181,10 +185,14 @@ static int afs_do_silly_unlink(struct afs_vnode *dvnode, struct afs_vnode *vnode
clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags);
}
}
- if (ret == 0 &&
- test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
- afs_edit_dir_remove(dvnode, &dentry->d_name,
- afs_edit_dir_for_unlink);
+ if (ret == 0) {
+ down_write(&dvnode->validate_lock);
+ if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags) &&
+ dvnode->status.data_version == dir_data_version)
+ afs_edit_dir_remove(dvnode, &dentry->d_name,
+ afs_edit_dir_for_unlink);
+ up_write(&dvnode->validate_lock);
+ }
}
kfree(scb);