Allocate inode tracing buffers before locking inode cluster

Trying to allocate memory while holding the inode cluster locked can cause deadlocks; a thread creating an inode will have the inode cluster locked and is stuck allocating memory, pdflush/kswapd are both trying to push out dirty pages and convert delayed allocations which need space in the log and xfsaild is trying to push on the tail of the log but is stuck trying to acquire the inode cluster lock.

I tried fixing this with KM_NOFS but turned a two-way deadlock into a three-way deadlock. This patch moves the allocation of the inode tracing buffers before we lock the inode cluster. We can also leak memory because we don't free these allocations if we return from this function early so use xfs_idestroy() to fully clean up the inode first.

Lachlan

@@ -818,19 +818,6 @@ xfs_iread(

	spin_lock_init(&ip->i_flags_lock);

	/*

- * Get pointer's to the on-disk inode and the buffer containing it.
- * If the inode number refers to a block outside the file system
- * then xfs_itobp() will return NULL. In this case we should
- * return NULL as well. Set i_blkno to 0 so that xfs_itobp() will
- * know that this is a new incore inode.
- */
- error = xfs_itobp(mp, tp, ip, &dip, &bp, bno, imap_flags, XFS_BUF_LOCK);
- if (error) {
- kmem_zone_free(xfs_inode_zone, ip);
- return error;
- }
-
- /*
* Initialize inode's trace buffers.
* Do this before xfs_iformat in case it adds entries. */
@@ -854,11 +841,24 @@ xfs_iread(
#endif

	/*

+ * Get pointer's to the on-disk inode and the buffer containing it.
+ * If the inode number refers to a block outside the file system
+ * then xfs_itobp() will return NULL. In this case we should
+ * return NULL as well. Set i_blkno to 0 so that xfs_itobp() will
+ * know that this is a new incore inode.
+ */
+ error = xfs_itobp(mp, tp, ip, &dip, &bp, bno, imap_flags, XFS_BUF_LOCK);
+ if (error) {
+ xfs_idestroy(ip);
+ return error;
+ }
+
+ /*

	 * If we got something that isn't an inode it means someone
	 * (nfs or dmi) has a stale handle.
	 */
	if (be16_to_cpu(dip->di_core.di_magic) != XFS_DINODE_MAGIC) {
-		kmem_zone_free(xfs_inode_zone, ip);
+		xfs_idestroy(ip);
		xfs_trans_brelse(tp, bp);
#ifdef DEBUG
		xfs_fs_cmn_err(CE_ALERT, mp, "xfs_iread: "
@@ -881,7 +881,7 @@ xfs_iread(
		xfs_dinode_from_disk(&ip->i_d, &dip->di_core);
		error = xfs_iformat(ip, dip);
		if (error)  {
-			kmem_zone_free(xfs_inode_zone, ip);
+			xfs_idestroy(ip);
			xfs_trans_brelse(tp, bp);
#ifdef DEBUG
			xfs_fs_cmn_err(CE_ALERT, mp, "xfs_iread: "

Seems sane, but I think it should be wrapped up in the xfs_inode_alloc() code added as part of the 'Make use of the init-once slab optimisation' patch I posted recently. This moves the initialisation of all things inode related into a separate function - xfs_inode_alloc() - instead of doing all these intialisations around the place....

Cheers,

Dave.

Dave Chinner
[email protected]

Okay, sounds like a good idea. I'll pull that patch in first.