xfs: inodes are new until the dentry cache is set up

Al Viro noticed a generic set of issues to do with filehandle lookup
racing with dentry cache setup. They involve a filehandle lookup
occurring while an inode is being created and the filehandle lookup
racing with the dentry creation for the real file. This can lead to
multiple dentries for the one path being instantiated. There are a
host of other issues around this same set of paths.

The underlying cause is that file handle lookup only waits on inode
cache instantiation rather than full dentry cache instantiation. XFS
is mostly immune to the problems discovered due to it's own internal
inode cache, but there are a couple of corner cases where races can
happen.

We currently clear the XFS_INEW flag when the inode is fully set up
after insertion into the cache. Newly allocated inodes are inserted
locked and so aren't usable until the allocation transaction
commits. This, however, occurs before the dentry and security
information is fully initialised and hence the inode is unlocked and
available for lookups to find too early.

To solve the problem, only clear the XFS_INEW flag for newly created
inodes once the dentry is fully instantiated. This means lookups
will retry until the XFS_INEW flag is removed from the inode and
hence avoids the race conditions in questions.

THis also means that xfs_create(), xfs_create_tmpfile() and
xfs_symlink() need to finish the setup of the inode in their error
paths if we had allocated the inode but failed later in the creation
process. xfs_symlink(), in particular, needed a lot of help to make
it's error handling match that of xfs_create().

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 9771b7ef62ed516bf12a7b3db58247ec12b78071..76a9f27832827db72fc58465389a619648a90b56 100644 (file)
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -439,11 +439,11 @@ again:
        *ipp = ip;
 
        /*
-        * If we have a real type for an on-disk inode, we can set ops(&unlock)
+        * If we have a real type for an on-disk inode, we can setup the inode
         * now.  If it's a new inode being created, xfs_ialloc will handle it.
         */
        if (xfs_iflags_test(ip, XFS_INEW) && ip->i_d.di_mode != 0)
-               xfs_setup_inode(ip);
+               xfs_setup_existing_inode(ip);
        return 0;
 
 out_error_or_again:

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index daafa1f6d2607722b338c8b5da458a979558d9b3..d0414f3059672bca2ab5c1386b136ca9ba525f1d 100644 (file)
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -818,7 +818,7 @@ xfs_ialloc(
        xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
        xfs_trans_log_inode(tp, ip, flags);
 
-       /* now that we have an i_mode we can setup inode ops and unlock */
+       /* now that we have an i_mode we can setup the inode structure */
        xfs_setup_inode(ip);
 
        *ipp = ip;
@@ -1235,12 +1235,14 @@ xfs_create(
        xfs_trans_cancel(tp, cancel_flags);
  out_release_inode:
        /*
-        * Wait until after the current transaction is aborted to
-        * release the inode.  This prevents recursive transactions
-        * and deadlocks from xfs_inactive.
+        * Wait until after the current transaction is aborted to finish the
+        * setup of the inode and release the inode.  This prevents recursive
+        * transactions and deadlocks from xfs_inactive.
         */
-       if (ip)
+       if (ip) {
+               xfs_finish_inode_setup(ip);
                IRELE(ip);
+       }
 
        xfs_qm_dqrele(udqp);
        xfs_qm_dqrele(gdqp);
@@ -1345,12 +1347,14 @@ xfs_create_tmpfile(
        xfs_trans_cancel(tp, cancel_flags);
  out_release_inode:
        /*
-        * Wait until after the current transaction is aborted to
-        * release the inode.  This prevents recursive transactions
-        * and deadlocks from xfs_inactive.
+        * Wait until after the current transaction is aborted to finish the
+        * setup of the inode and release the inode.  This prevents recursive
+        * transactions and deadlocks from xfs_inactive.
         */
-       if (ip)
+       if (ip) {
+               xfs_finish_inode_setup(ip);
                IRELE(ip);
+       }
 
        xfs_qm_dqrele(udqp);
        xfs_qm_dqrele(gdqp);

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 86cd6b39bed7be1dc4bd72be82e9a40b9c8b9825..8e82b41d2050c2a2266eb38310453cb9d3f535ba 100644 (file)
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -390,6 +390,28 @@ int                xfs_zero_eof(struct xfs_inode *, xfs_off_t, xfs_fsize_t);
 int            xfs_iozero(struct xfs_inode *, loff_t, size_t);
 
 
+/* from xfs_iops.c */
+/*
+ * When setting up a newly allocated inode, we need to call
+ * xfs_finish_inode_setup() once the inode is fully instantiated at
+ * the VFS level to prevent the rest of the world seeing the inode
+ * before we've completed instantiation. Otherwise we can do it
+ * the moment the inode lookup is complete.
+ */
+extern void xfs_setup_inode(struct xfs_inode *ip);
+static inline void xfs_finish_inode_setup(struct xfs_inode *ip)
+{
+       xfs_iflags_clear(ip, XFS_INEW);
+       barrier();
+       unlock_new_inode(VFS_I(ip));
+}
+
+static inline void xfs_setup_existing_inode(struct xfs_inode *ip)
+{
+       xfs_setup_inode(ip);
+       xfs_finish_inode_setup(ip);
+}
+
 #define IHOLD(ip) \
 do { \
        ASSERT(atomic_read(&VFS_I(ip)->i_count) > 0) ; \

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index d919ad7b16bf9acbe01c6531a9254b372426911a..d7782ae1af3c1b966ac6303ccfab64d36ceeed96 100644 (file)
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -187,6 +187,8 @@ xfs_generic_create(
        else
                d_instantiate(dentry, inode);
 
+       xfs_finish_inode_setup(ip);
+
  out_free_acl:
        if (default_acl)
                posix_acl_release(default_acl);
@@ -195,6 +197,7 @@ xfs_generic_create(
        return error;
 
  out_cleanup_inode:
+       xfs_finish_inode_setup(ip);
        if (!tmpfile)
                xfs_cleanup_inode(dir, inode, dentry);
        iput(inode);
@@ -367,9 +370,11 @@ xfs_vn_symlink(
                goto out_cleanup_inode;
 
        d_instantiate(dentry, inode);
+       xfs_finish_inode_setup(cip);
        return 0;
 
  out_cleanup_inode:
+       xfs_finish_inode_setup(cip);
        xfs_cleanup_inode(dir, inode, dentry);
        iput(inode);
  out:
@@ -1236,16 +1241,12 @@ xfs_diflags_to_iflags(
 }
 
 /*
- * Initialize the Linux inode, set up the operation vectors and
- * unlock the inode.
- *
- * When reading existing inodes from disk this is called directly
- * from xfs_iget, when creating a new inode it is called from
- * xfs_ialloc after setting up the inode.
+ * Initialize the Linux inode and set up the operation vectors.
  *
- * We are always called with an uninitialised linux inode here.
- * We need to initialise the necessary fields and take a reference
- * on it.
+ * When reading existing inodes from disk this is called directly from xfs_iget,
+ * when creating a new inode it is called from xfs_ialloc after setting up the
+ * inode. These callers have different criteria for clearing XFS_INEW, so leave
+ * it up to the caller to deal with unlocking the inode appropriately.
  */
 void
 xfs_setup_inode(
@@ -1332,9 +1333,4 @@ xfs_setup_inode(
                inode_has_no_xattr(inode);
                cache_no_acl(inode);
        }
-
-       xfs_iflags_clear(ip, XFS_INEW);
-       barrier();
-
-       unlock_new_inode(inode);
 }

diff --git a/fs/xfs/xfs_iops.h b/fs/xfs/xfs_iops.h
index ea7a98e9cb7048820bfa69c5bc294ccbe4102709..a0f84abb0d09d34e0893e6c61b6e01c287a9946a 100644 (file)
--- a/fs/xfs/xfs_iops.h
+++ b/fs/xfs/xfs_iops.h
@@ -25,8 +25,6 @@ extern const struct file_operations xfs_dir_file_operations;
 
 extern ssize_t xfs_vn_listxattr(struct dentry *, char *data, size_t size);
 
-extern void xfs_setup_inode(struct xfs_inode *);
-
 /*
  * Internal setattr interfaces.
  */

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 53cc2aaf8d2bdfedc12247ae5055feaa95ae31a6..c6b22e1e77ed1e647a35baf365568970593da0ad 100644 (file)
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -719,6 +719,7 @@ xfs_qm_qino_alloc(
        xfs_trans_t     *tp;
        int             error;
        int             committed;
+       bool            need_alloc = true;
 
        *ip = NULL;
        /*
@@ -747,6 +748,7 @@ xfs_qm_qino_alloc(
                                return error;
                        mp->m_sb.sb_gquotino = NULLFSINO;
                        mp->m_sb.sb_pquotino = NULLFSINO;
+                       need_alloc = false;
                }
        }
 
@@ -758,7 +760,7 @@ xfs_qm_qino_alloc(
                return error;
        }
 
-       if (!*ip) {
+       if (need_alloc) {
                error = xfs_dir_ialloc(&tp, NULL, S_IFREG, 1, 0, 0, 1, ip,
                                                                &committed);
                if (error) {
@@ -794,11 +796,14 @@ xfs_qm_qino_alloc(
        spin_unlock(&mp->m_sb_lock);
        xfs_log_sb(tp);
 
-       if ((error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES))) {
+       error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
+       if (error) {
+               ASSERT(XFS_FORCED_SHUTDOWN(mp));
                xfs_alert(mp, "%s failed (error %d)!", __func__, error);
-               return error;
        }
-       return 0;
+       if (need_alloc)
+               xfs_finish_inode_setup(*ip);
+       return error;
 }
 
 

diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
index 25791df6f638c7a77421840e07b35204a5589f3f..3df411eadb867c83388bdec2995ca41a7a815d7e 100644 (file)
--- a/fs/xfs/xfs_symlink.c
+++ b/fs/xfs/xfs_symlink.c
@@ -177,7 +177,7 @@ xfs_symlink(
        int                     pathlen;
        struct xfs_bmap_free    free_list;
        xfs_fsblock_t           first_block;
-       bool                    unlock_dp_on_error = false;
+       bool                    unlock_dp_on_error = false;
        uint                    cancel_flags;
        int                     committed;
        xfs_fileoff_t           first_fsb;
@@ -221,7 +221,7 @@ xfs_symlink(
                        XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
                        &udqp, &gdqp, &pdqp);
        if (error)
-               goto std_return;
+               return error;
 
        tp = xfs_trans_alloc(mp, XFS_TRANS_SYMLINK);
        cancel_flags = XFS_TRANS_RELEASE_LOG_RES;
@@ -241,7 +241,7 @@ xfs_symlink(
        }
        if (error) {
                cancel_flags = 0;
-               goto error_return;
+               goto out_trans_cancel;
        }
 
        xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
@@ -252,7 +252,7 @@ xfs_symlink(
         */
        if (dp->i_d.di_flags & XFS_DIFLAG_NOSYMLINKS) {
                error = -EPERM;
-               goto error_return;
+               goto out_trans_cancel;
        }
 
        /*
@@ -261,7 +261,7 @@ xfs_symlink(
        error = xfs_trans_reserve_quota(tp, mp, udqp, gdqp,
                                                pdqp, resblks, 1, 0);
        if (error)
-               goto error_return;
+               goto out_trans_cancel;
 
        /*
         * Check for ability to enter directory entry, if no space reserved.
@@ -269,7 +269,7 @@ xfs_symlink(
        if (!resblks) {
                error = xfs_dir_canenter(tp, dp, link_name);
                if (error)
-                       goto error_return;
+                       goto out_trans_cancel;
        }
        /*
         * Initialize the bmap freelist prior to calling either
@@ -282,15 +282,14 @@ xfs_symlink(
         */
        error = xfs_dir_ialloc(&tp, dp, S_IFLNK | (mode & ~S_IFMT), 1, 0,
                               prid, resblks > 0, &ip, NULL);
-       if (error) {
-               if (error == -ENOSPC)
-                       goto error_return;
-               goto error1;
-       }
+       if (error)
+               goto out_trans_cancel;
 
        /*
-        * An error after we've joined dp to the transaction will result in the
-        * transaction cancel unlocking dp so don't do it explicitly in the
+        * Now we join the directory inode to the transaction.  We do not do it
+        * earlier because xfs_dir_ialloc might commit the previous transaction
+        * (and release all the locks).  An error from here on will result in
+        * the transaction cancel unlocking dp so don't do it explicitly in the
         * error path.
         */
        xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
@@ -330,7 +329,7 @@ xfs_symlink(
                                  XFS_BMAPI_METADATA, &first_block, resblks,
                                  mval, &nmaps, &free_list);
                if (error)
-                       goto error2;
+                       goto out_bmap_cancel;
 
                if (resblks)
                        resblks -= fs_blocks;
@@ -348,7 +347,7 @@ xfs_symlink(
                                               BTOBB(byte_cnt), 0);
                        if (!bp) {
                                error = -ENOMEM;
-                               goto error2;
+                               goto out_bmap_cancel;
                        }
                        bp->b_ops = &xfs_symlink_buf_ops;
 
@@ -378,7 +377,7 @@ xfs_symlink(
        error = xfs_dir_createname(tp, dp, link_name, ip->i_ino,
                                        &first_block, &free_list, resblks);
        if (error)
-               goto error2;
+               goto out_bmap_cancel;
        xfs_trans_ichgtime(tp, dp, XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
        xfs_trans_log_inode(tp, dp, XFS_ILOG_CORE);
 
@@ -392,10 +391,13 @@ xfs_symlink(
        }
 
        error = xfs_bmap_finish(&tp, &free_list, &committed);
-       if (error) {
-               goto error2;
-       }
+       if (error)
+               goto out_bmap_cancel;
+
        error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
+       if (error)
+               goto out_release_inode;
+
        xfs_qm_dqrele(udqp);
        xfs_qm_dqrele(gdqp);
        xfs_qm_dqrele(pdqp);
@@ -403,20 +405,28 @@ xfs_symlink(
        *ipp = ip;
        return 0;
 
- error2:
-       IRELE(ip);
- error1:
+out_bmap_cancel:
        xfs_bmap_cancel(&free_list);
        cancel_flags |= XFS_TRANS_ABORT;
- error_return:
+out_trans_cancel:
        xfs_trans_cancel(tp, cancel_flags);
+out_release_inode:
+       /*
+        * Wait until after the current transaction is aborted to finish the
+        * setup of the inode and release the inode.  This prevents recursive
+        * transactions and deadlocks from xfs_inactive.
+        */
+       if (ip) {
+               xfs_finish_inode_setup(ip);
+               IRELE(ip);
+       }
+
        xfs_qm_dqrele(udqp);
        xfs_qm_dqrele(gdqp);
        xfs_qm_dqrele(pdqp);
 
        if (unlock_dp_on_error)
                xfs_iunlock(dp, XFS_ILOCK_EXCL);
- std_return:
        return error;
 }