linux-kernel - [PATCH 4.11 099/115] xfs: drop iolock from reclaim context to appease lockdep

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Date:   Mon,  5 Jun 2017 18:18:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Brian Foster <bfoster@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>
Subject: [PATCH 4.11 099/115] xfs: drop iolock from reclaim context to appease lockdep

4.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Brian Foster <bfoster@...hat.com>

commit 3b4683c294095b5f777c03307ef8c60f47320e12 upstream.

Lockdep complains about use of the iolock in inode reclaim context
because it doesn't understand that reclaim has the last reference to
the inode, and thus an iolock->reclaim->iolock deadlock is not
possible.

The iolock is technically not necessary in xfs_inactive() and was
only added to appease an assert in xfs_free_eofblocks(), which can
be called from other non-reclaim contexts. Therefore, just kill the
assert and drop the use of the iolock from reclaim context to quiet
lockdep.

Signed-off-by: Brian Foster <bfoster@...hat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/xfs/xfs_bmap_util.c |    8 +++-----
 fs/xfs/xfs_inode.c     |    9 +++++----
 2 files changed, 8 insertions(+), 9 deletions(-)

--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -904,9 +904,9 @@ xfs_can_free_eofblocks(struct xfs_inode
 }
 
 /*
- * This is called by xfs_inactive to free any blocks beyond eof
- * when the link count isn't zero and by xfs_dm_punch_hole() when
- * punching a hole to EOF.
+ * This is called to free any blocks beyond eof. The caller must hold
+ * IOLOCK_EXCL unless we are in the inode reclaim path and have the only
+ * reference to the inode.
  */
 int
 xfs_free_eofblocks(
@@ -921,8 +921,6 @@ xfs_free_eofblocks(
 	struct xfs_bmbt_irec	imap;
 	struct xfs_mount	*mp = ip->i_mount;
 
-	ASSERT(xfs_isilocked(ip, XFS_IOLOCK_EXCL));
-
 	/*
 	 * Figure out if there are any blocks beyond the end
 	 * of the file.  If not, then there is nothing to do.
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1906,12 +1906,13 @@ xfs_inactive(
 		 * force is true because we are evicting an inode from the
 		 * cache. Post-eof blocks must be freed, lest we end up with
 		 * broken free space accounting.
+		 *
+		 * Note: don't bother with iolock here since lockdep complains
+		 * about acquiring it in reclaim context. We have the only
+		 * reference to the inode at this point anyways.
 		 */
-		if (xfs_can_free_eofblocks(ip, true)) {
-			xfs_ilock(ip, XFS_IOLOCK_EXCL);
+		if (xfs_can_free_eofblocks(ip, true))
 			xfs_free_eofblocks(ip);
-			xfs_iunlock(ip, XFS_IOLOCK_EXCL);
-		}
 
 		return;
 	}