xfs: free the EFI entries from AIL on forced shutdown

The extent free intention (EFI) and extent free done (EFD) log items are in separate transactions. It is possible that the EFI can be pushed to the AIL before a forced shutdown where it gets stuck for following reasons:

No EFD. If freeing the extent fails in xfs_bmap_finish() or xfs_recover_process_efi(), then the corresponding extent free done (EFD) entry will not be created.

EFD IOP Abort processing. If xfs_trans_cancel() is called with an abort flag, or if the xfs_trans_commit() is called when the file system is in forced shutdown or if the log buffer write fails, then the EFD iop commands will not remove the EFI from the AIL.

Index: b/fs/xfs/xfs_extfree_item.c
===================================================================

fs/xfs/xfs_extfree_item.c +0 -1

@@ -420,8 +420,15 @@ STATIC void
 xfs_efd_item_unlock(
 	struct xfs_log_item	*lip)
 {
-	if (lip->li_flags & XFS_LI_ABORTED)

fs/xfs/xfs_extfree_item.c +1 -2

@@ -439,10 +446,15 @@ xfs_efd_item_committed(
 	struct xfs_efd_log_item	*efdp = EFD_ITEM(lip);
 
 	/*
-	 * If we got a log I/O error, it's always the case that the LR with the
-	 * EFI got unpinned and freed before the EFD got aborted.
+	 * If we got a log I/O error and the EFI is also in this buffer, it

Index: b/fs/xfs/xfs_log_recover.c
===================================================================

fs/xfs/xfs_log_recover.c +7 -10

@@ -3634,20 +3634,23 @@ xlog_recover_process_data(
 /*
  * Process an extent free intent item that was recovered from
  * the log.  We need to free the extents that it describes.
+ * The caller will free all EFI entries on error.
  */
 STATIC int
 xlog_recover_process_efi(
-	xfs_mount_t		*mp,
-	xfs_efi_log_item_t	*efip)
+	struct xfs_mount	*mp,
+	struct xfs_efi_log_item	*efip)
 {
-	xfs_efd_log_item_t	*efdp;
-	xfs_trans_t		*tp;
+	struct xfs_efd_log_item	*efdp;
+	struct xfs_trans	*tp;
 	int			i;
 	int			error = 0;
 	xfs_extent_t		*extp;
 	xfs_fsblock_t		startblock_fsb;
 
 	ASSERT(!test_bit(XFS_EFI_RECOVERED, &efip->efi_flags));
+	/* All paths need the XFS_EFI_RECOVERED flag set. Do it here. */
+	set_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
 
 	/*
 	 * First check the validity of the extents described by the

@@ -3662,12 +3665,6 @@ xlog_recover_process_efi(
 		    (extp->ext_len == 0) ||
 		    (startblock_fsb >= mp->m_sb.sb_dblocks) ||
 		    (extp->ext_len >= mp->m_sb.sb_agblocks)) {
-			/*
-			 * This will pull the EFI from the AIL and
-			 * free the memory associated with it.
-			 */
-			set_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
-			xfs_efi_release(efip, efip->efi_format.efi_nextents);
 			return XFS_ERROR(EIO);
 		}
 	}

fs/xfs/xfs_log_recover.c +2 -3

@@ -3718,8 +3714,8 @@ STATIC int
 xlog_recover_process_efis(
 	struct xlog	*log)
 {
-	xfs_log_item_t		*lip;
-	xfs_efi_log_item_t	*efip;
+	struct xfs_log_item	*lip;
+	struct xfs_efi_log_item	*efip;
 	int			error = 0;
 	struct xfs_ail_cursor	cur;
 	struct xfs_ail		*ailp;

@@ -3753,12 +3749,13 @@ xlog_recover_process_efis(
 		error = xlog_recover_process_efi(log->l_mp, efip);
 		spin_lock(&ailp->xa_lock);
 		if (error)
-			goto out;

Quoted 8 lines · Mark Tinguely

The extent free intention (EFI) and extent free done (EFD) log items are in separate transactions. It is possible that the EFI can be pushed to the AIL before a forced shutdown where it gets stuck for following reasons:

No EFD. If freeing the extent fails in xfs_bmap_finish() or xfs_recover_process_efi(), then the corresponding extent free done (EFD) entry will not be created.

You don't handle the xfs_bmap_finish() case properly - the patch only addresses the case where the EFD was created and contains a reference to the EFI. The only time we can have an EFI in the AIL without an EFD pointing to it is if xfs_trans_reserve() call in xfs_bmap_finish() fails due to a shutdown. That failure case leaks the EFI reference that is supposed to be passed to the EFD...

Quoted 4 lines

EFD IOP Abort processing. If xfs_trans_cancel() is called with an abort flag, or if the xfs_trans_commit() is called when the file system is in forced shutdown or if the log buffer write fails, then the EFD iop commands will not remove the EFI from the AIL.

Which they should, because after xfs_trans_get_efd(), the EFD owns the reference to the EFI. Hence aborting the EFD should release the EFI reference it owns.

Quoted 10 lines

Index: b/fs/xfs/xfs_extfree_item.c
===================================================================

fs/xfs/xfs_extfree_item.c +0 -1

@@ -420,8 +420,15 @@ STATIC void
  xfs_efd_item_unlock(
  	struct xfs_log_item	*lip)
  {
-	if (lip->li_flags&  XFS_LI_ABORTED)

fs/xfs/xfs_extfree_item.c STATIC void · line 432

Quoted 10 lines

fs/xfs/xfs_extfree_item.c +8 -0

+	/*
+	 * Clear the EFI if on AIL when aborting xfs_bmap_finish.
+	 * The forced shutdown will force the log, so other EFDs
+	 * should not be processed from the CIL.
+	 */
+	if (lip->li_flags&  XFS_LI_ABORTED) {
+		xfs_efi_clear_ail(lip->li_ailp);
  		xfs_efd_item_free(EFD_ITEM(lip));
+	}
  }

So, we abort one EFI, so we kill every EFI in the filesystem? We want to be able to cancel and rollback transactions eventually, and this will prevent us from being able to do that as it will kill EFIs unrelated to the EFD being aborted.

AFAICT, all this needs to do is:

	if (!(lip->li_flags&  XFS_LI_ABORTED))
		return;

	xfs_efi_release(efdp->efd_efip, efdp->efd_format.efd_nextents);
	xfs_efd_item_free(efdp);

i.e. before freeing the EFD, release the reference to the EFI that it was passed.

Quoted 7 lines

fs/xfs/xfs_extfree_item.c +1 -2

@@ -439,10 +446,15 @@ xfs_efd_item_committed(
  	struct xfs_efd_log_item	*efdp = EFD_ITEM(lip);
 
  	/*
-	 * If we got a log I/O error, it's always the case that the LR with the
-	 * EFI got unpinned and freed before the EFD got aborted.
+	 * If we got a log I/O error and the EFI is also in this buffer, it

fs/xfs/xfs_extfree_item.c xfs_efd_item_committed( · line 458

Quoted 10 lines

fs/xfs/xfs_extfree_item.c +7 -1

+	 * will be unpinned and freed before the EFD got aborted. But the EFI
+	 * is in an earlier transaction and could be on the AIL when the log
+	 * I/O error happened for this EFD. In that case, manually remove the
+	 * remaining EFIs from the AIL.
  	 */
-	if (!(lip->li_flags&  XFS_LI_ABORTED))
+	if (lip->li_flags&  XFS_LI_ABORTED)
+		xfs_efi_clear_ail(lip->li_ailp);
+	else
  		xfs_efi_release(efdp->efd_efip, efdp->efd_format.efd_nextents);

Same here - we can simply always call xfs_efi_release() and we'll end up doing the right thing w.r.t. the EFi reference count.

And if we do the right thing with the EFI reference count when aborting the EFI (i.e. call __xfs_efi_release() rather than freeing it) the aborting of transactions will correctly free all the references to the EFI and remove them from the AIL.

The only case we
then have to handle specially is the xfs_trans_reserve failure in xfs_bmap_finish(), where we need to release the EFI directly in the error path.

That gets rid of the "big hammer" error handling for normal runtime shutdown that xfs_efi_clear_ail(). i.e. we need to fix the reference count handling, not work around it.

Quoted 46 lines

Index: b/fs/xfs/xfs_log_recover.c
===================================================================

fs/xfs/xfs_log_recover.c +7 -10

@@ -3634,20 +3634,23 @@ xlog_recover_process_data(
  /*
   * Process an extent free intent item that was recovered from
   * the log.  We need to free the extents that it describes.
+ * The caller will free all EFI entries on error.
   */
  STATIC int
  xlog_recover_process_efi(
-	xfs_mount_t		*mp,
-	xfs_efi_log_item_t	*efip)
+	struct xfs_mount	*mp,
+	struct xfs_efi_log_item	*efip)
  {
-	xfs_efd_log_item_t	*efdp;
-	xfs_trans_t		*tp;
+	struct xfs_efd_log_item	*efdp;
+	struct xfs_trans	*tp;
  	int			i;
  	int			error = 0;
  	xfs_extent_t		*extp;
  	xfs_fsblock_t		startblock_fsb;
 
  	ASSERT(!test_bit(XFS_EFI_RECOVERED,&efip->efi_flags));
+	/* All paths need the XFS_EFI_RECOVERED flag set. Do it here. */
+	set_bit(XFS_EFI_RECOVERED,&efip->efi_flags);
 
  	/*
  	 * First check the validity of the extents described by the

@@ -3662,12 +3665,6 @@ xlog_recover_process_efi(
  		    (extp->ext_len == 0) ||
  		    (startblock_fsb>= mp->m_sb.sb_dblocks) ||
  		    (extp->ext_len>= mp->m_sb.sb_agblocks)) {
-			/*
-			 * This will pull the EFI from the AIL and
-			 * free the memory associated with it.
-			 */
-			set_bit(XFS_EFI_RECOVERED,&efip->efi_flags);
-			xfs_efi_release(efip, efip->efi_format.efi_nextents);
  			return XFS_ERROR(EIO);
  		}
  	}

fs/xfs/xfs_log_recover.c xlog_recover_process_efi( · line 3688

Quoted 6 lines

fs/xfs/xfs_log_recover.c +0 -1

@@ -3687,7 +3684,6 @@ xlog_recover_process_efi(
  					 extp->ext_len);
  	}
 
-	set_bit(XFS_EFI_RECOVERED,&efip->efi_flags);
  	error = xfs_trans_commit(tp, 0);
  	return error;

This is basically saying "xfs_efi_release() should drop both the AIL and the EFD reference as we really only only have one reference". I think we should simply remove the XFS_EFI_RECOVERED bit from the reference counting code, and simply subtract one of the EFI references in xlog_recover_efi_pass2() where we insert the EFI into the AIL, so that it behaves exactly like the runtime case when later processing the EFDs.

That is, in xlog_recover_efd_pass2() when we find a matching EFD we simply call xfs_efi_release() and that does all the freeing because we're removing the EFD reference which is the only remaining reference.

Then in xlog_recover_process_efi(), we simply call xfs_efi_release() for the error cases to drop the last reference to the EFI, otherwise the commit of the EFD will free it because it calls xfs_efi_release() appropriately.

Quoted 18 lines

fs/xfs/xfs_log_recover.c +2 -3

@@ -3718,8 +3714,8 @@ STATIC int
  xlog_recover_process_efis(
  	struct xlog	*log)
  {
-	xfs_log_item_t		*lip;
-	xfs_efi_log_item_t	*efip;
+	struct xfs_log_item	*lip;
+	struct xfs_efi_log_item	*efip;
  	int			error = 0;
  	struct xfs_ail_cursor	cur;
  	struct xfs_ail		*ailp;

@@ -3753,12 +3749,13 @@ xlog_recover_process_efis(
  		error = xlog_recover_process_efi(log->l_mp, efip);
  		spin_lock(&ailp->xa_lock);
  		if (error)
-			goto out;

fs/xfs/xfs_log_recover.c xlog_recover_process_efis( · line 3760

Quoted 10 lines

fs/xfs/xfs_log_recover.c +3 -1

+			break;
  		lip = xfs_trans_ail_cursor_next(ailp,&cur);
  	}
-out:
  	xfs_trans_ail_cursor_done(ailp,&cur);
  	spin_unlock(&ailp->xa_lock);
+	if (error)
+		xfs_efi_clear_ail(ailp);
  	return error;
  }

If we fix the reference counting, then I think all we need here is:

	int	error = 0;

	while (ail cursor next) {
		....
		if (!error)
			error = xlog_recover_process_efi()
		else
			xfs_efi_release(efip)
		....
	}

So that any error will trigger freeing of all the other unprocessed EFIs on the AIL that are pending recovery without needing any more special looping....

Quoted 4 lines · Dave Chinner

The only case we
then have to handle specially is the xfs_trans_reserve failure in xfs_bmap_finish(), where we need to release the EFI directly in the error path.

any reason to not move the efd creation earlier to not special case it?

Quoted 22 lines · Dave Chinner

Quoted 7 lines · Mark Tinguely

fs/xfs/xfs_extfree_item.c +1 -2

@@ -439,10 +446,15 @@ xfs_efd_item_committed(
 	struct xfs_efd_log_item	*efdp = EFD_ITEM(lip);
 
 	/*
-	 * If we got a log I/O error, it's always the case that the LR with the
-	 * EFI got unpinned and freed before the EFD got aborted.
+	 * If we got a log I/O error and the EFI is also in this buffer, it

fs/xfs/xfs_extfree_item.c xfs_efd_item_committed( · line 458

Quoted 10 lines

fs/xfs/xfs_extfree_item.c +7 -1

+	 * will be unpinned and freed before the EFD got aborted. But the EFI
+	 * is in an earlier transaction and could be on the AIL when the log
+	 * I/O error happened for this EFD. In that case, manually remove the
+	 * remaining EFIs from the AIL.
 	 */
-	if (!(lip->li_flags&  XFS_LI_ABORTED))
+	if (lip->li_flags&  XFS_LI_ABORTED)
+		xfs_efi_clear_ail(lip->li_ailp);
+	else
 		xfs_efi_release(efdp->efd_efip, efdp->efd_format.efd_nextents);

Same here - we can simply always call xfs_efi_release() and we'll end up doing the right thing w.r.t. the EFi reference count.

Quoted 4 lines

And if we do the right thing with the EFI reference count when aborting the EFI (i.e. call __xfs_efi_release() rather than freeing it) the aborting of transactions will correctly free all the references to the EFI and remove them from the AIL.

This is fine if the EFI made it to the AIL before the log abort - which it may or may not have done.

Log errors will not force the log. The call to xfs_trans_committed_bulk() with the abort flag set will not place the EFI on the AIL (takes the iop_unpin/continue path).

Your proposal of changing xfs_efi_committed() from freeing the EFI to a call to __xfs_efi_release() and changing xfs_efd_committed() to xfs_efi_release() will do the right thing for the counters and removing both the EFI/EFD entries, but it will also want to remove the non-existent EFI entry from the AIL. I do not like adding the EFI to the AIL in the abort path.

Quoted 4 lines

The only case we
then have to handle specially is the xfs_trans_reserve failure in xfs_bmap_finish(), where we need to release the EFI directly in the error path.

any reason to not move the efd creation earlier to not special case it?