ocfs2: fix rare stale inode errors when exporting via nfs

For nfs exporting, ocfs2_get_dentry() returns the dentry for fh.
ocfs2_get_dentry() may read from disk when the inode is not in memory,
without any cross cluster lock. this leads to the file system loading a
stale inode.

This patch fixes above problem.

Solution is that in case of inode is not in memory, we get the cluster
lock(PR) of alloc inode where the inode in question is allocated from (this
causes node on which deletion is done sync the alloc inode) before reading
out the inode itsself. then we check the bitmap in the group (the inode in
question allcated from) to see if the bit is clear. if it's clear then it's
stale. if the bit is set, we then check generation as the existing code
does.

We have to read out the inode in question from disk first to know its alloc
slot and allot bit. And if its not stale we read it out using ocfs2_iget().
The second read should then be from cache.

And also we have to add a per superblock nfs_sync_lock to cover the lock for
alloc inode and that for inode in question. this is because ocfs2_get_dentry()
and ocfs2_delete_inode() lock on them in reverse order. nfs_sync_lock is locked
in EX mode in ocfs2_get_dentry() and in PR mode in ocfs2_delete_inode(). so
that mutliple ocfs2_delete_inode() can run concurrently in normal case.

[mfasheh@suse.com: build warning fixes and comment cleanups]
Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Acked-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 159 insertions, 0 deletions

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 4c1399c..b4ca591 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -2185,3 +2185,162 @@ out:
 
 	return ret;
 }
+
+/*
+ * Read the inode specified by blkno to get suballoc_slot and
+ * suballoc_bit.
+ */
+static int ocfs2_get_suballoc_slot_bit(struct ocfs2_super *osb, u64 blkno,
+				       u16 *suballoc_slot, u16 *suballoc_bit)
+{
+	int status;
+	struct buffer_head *inode_bh = NULL;
+	struct ocfs2_dinode *inode_fe;
+
+	mlog_entry("blkno: %llu\n", blkno);
+
+	/* dirty read disk */
+	status = ocfs2_read_blocks_sync(osb, blkno, 1, &inode_bh);
+	if (status < 0) {
+		mlog(ML_ERROR, "read block %llu failed %d\n", blkno, status);
+		goto bail;
+	}
+
+	inode_fe = (struct ocfs2_dinode *) inode_bh->b_data;
+	if (!OCFS2_IS_VALID_DINODE(inode_fe)) {
+		mlog(ML_ERROR, "invalid inode %llu requested\n", blkno);
+		status = -EINVAL;
+		goto bail;
+	}
+
+	if (le16_to_cpu(inode_fe->i_suballoc_slot) != OCFS2_INVALID_SLOT &&
+	    (u32)le16_to_cpu(inode_fe->i_suballoc_slot) > osb->max_slots - 1) {
+		mlog(ML_ERROR, "inode %llu has invalid suballoc slot %u\n",
+		     blkno, (u32)le16_to_cpu(inode_fe->i_suballoc_slot));
+		status = -EINVAL;
+		goto bail;
+	}
+
+	if (suballoc_slot)
+		*suballoc_slot = le16_to_cpu(inode_fe->i_suballoc_slot);
+	if (suballoc_bit)
+		*suballoc_bit = le16_to_cpu(inode_fe->i_suballoc_bit);
+
+bail:
+	brelse(inode_bh);
+
+	mlog_exit(status);
+	return status;
+}
+
+/*
+ * test whether bit is SET in allocator bitmap or not.  on success, 0
+ * is returned and *res is 1 for SET; 0 otherwise.  when fails, errno
+ * is returned and *res is meaningless.  Call this after you have
+ * cluster locked against suballoc, or you may get a result based on
+ * non-up2date contents
+ */
+static int ocfs2_test_suballoc_bit(struct ocfs2_super *osb,
+				   struct inode *suballoc,
+				   struct buffer_head *alloc_bh, u64 blkno,
+				   u16 bit, int *res)
+{
+	struct ocfs2_dinode *alloc_fe;
+	struct ocfs2_group_desc *group;
+	struct buffer_head *group_bh = NULL;
+	u64 bg_blkno;
+	int status;
+
+	mlog_entry("blkno: %llu bit: %u\n", blkno, (unsigned int)bit);
+
+	alloc_fe = (struct ocfs2_dinode *)alloc_bh->b_data;
+	if ((bit + 1) > ocfs2_bits_per_group(&alloc_fe->id2.i_chain)) {
+		mlog(ML_ERROR, "suballoc bit %u out of range of %u\n",
+		     (unsigned int)bit,
+		     ocfs2_bits_per_group(&alloc_fe->id2.i_chain));
+		status = -EINVAL;
+		goto bail;
+	}
+
+	bg_blkno = ocfs2_which_suballoc_group(blkno, bit);
+	status = ocfs2_read_group_descriptor(suballoc, alloc_fe, bg_blkno,
+					     &group_bh);
+	if (status < 0) {
+		mlog(ML_ERROR, "read group %llu failed %d\n", bg_blkno, status);
+		goto bail;
+	}
+
+	group = (struct ocfs2_group_desc *) group_bh->b_data;
+	*res = ocfs2_test_bit(bit, (unsigned long *)group->bg_bitmap);
+
+bail:
+	brelse(group_bh);
+
+	mlog_exit(status);
+	return status;
+}
+
+/*
+ * Test if the bit representing this inode (blkno) is set in the
+ * suballocator.
+ *
+ * On success, 0 is returned and *res is 1 for SET; 0 otherwise.
+ *
+ * In the event of failure, a negative value is returned and *res is
+ * meaningless.
+ *
+ * Callers must make sure to hold nfs_sync_lock to prevent
+ * ocfs2_delete_inode() on another node from accessing the same
+ * suballocator concurrently.
+ */
+int ocfs2_test_inode_bit(struct ocfs2_super *osb, u64 blkno, int *res)
+{
+	int status;
+	u16 suballoc_bit = 0, suballoc_slot = 0;
+	struct inode *inode_alloc_inode;
+	struct buffer_head *alloc_bh = NULL;
+
+	mlog_entry("blkno: %llu", blkno);
+
+	status = ocfs2_get_suballoc_slot_bit(osb, blkno, &suballoc_slot,
+					     &suballoc_bit);
+	if (status < 0) {
+		mlog(ML_ERROR, "get alloc slot and bit failed %d\n", status);
+		goto bail;
+	}
+
+	inode_alloc_inode =
+		ocfs2_get_system_file_inode(osb, INODE_ALLOC_SYSTEM_INODE,
+					    suballoc_slot);
+	if (!inode_alloc_inode) {
+		/* the error code could be inaccurate, but we are not able to
+		 * get the correct one. */
+		status = -EINVAL;
+		mlog(ML_ERROR, "unable to get alloc inode in slot %u\n",
+		     (u32)suballoc_slot);
+		goto bail;
+	}
+
+	mutex_lock(&inode_alloc_inode->i_mutex);
+	status = ocfs2_inode_lock(inode_alloc_inode, &alloc_bh, 0);
+	if (status < 0) {
+		mutex_unlock(&inode_alloc_inode->i_mutex);
+		mlog(ML_ERROR, "lock on alloc inode on slot %u failed %d\n",
+		     (u32)suballoc_slot, status);
+		goto bail;
+	}
+
+	status = ocfs2_test_suballoc_bit(osb, inode_alloc_inode, alloc_bh,
+					 blkno, suballoc_bit, res);
+	if (status < 0)
+		mlog(ML_ERROR, "test suballoc bit failed %d\n", status);
+
+	ocfs2_inode_unlock(inode_alloc_inode, 0);
+	mutex_unlock(&inode_alloc_inode->i_mutex);
+
+	iput(inode_alloc_inode);
+	brelse(alloc_bh);
+bail:
+	mlog_exit(status);
+	return status;
+}