Patch "udf: Fix deadlock between writeback and udf_setsize()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

udf: Fix deadlock between writeback and udf_setsize()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
udf-fix-deadlock-between-writeback-and-udf_setsize.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Tue, 13 Jun 2017 16:20:25 +0200
Subject: udf: Fix deadlock between writeback and udf_setsize()

From: Jan Kara <[email protected]>

commit f2e95355891153f66d4156bf3a142c6489cd78c6 upstream.

udf_setsize() called truncate_setsize() with i_data_sem held. Thus truncate_pagecache() called from truncate_setsize() could lock a page under i_data_sem which can deadlock as page lock ranks below i_data_sem - e. g. writeback can hold page lock and try to acquire i_data_sem to map a block.

Fix the problem by moving truncate_setsize() calls from under i_data_sem. It is safe for us to change i_size without holding i_data_sem as all the places that depend on i_size being stable already hold inode_lock.

---
 fs/udf/inode.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -1243,8 +1243,8 @@ int udf_setsize(struct inode *inode, lof
 			return err;
 		}
 set_size:
-		truncate_setsize(inode, newsize);
 		up_write(&iinfo->i_data_sem);
+		truncate_setsize(inode, newsize);
 	} else {
 		if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
 			down_write(&iinfo->i_data_sem);

@@ -1261,9 +1261,9 @@ set_size:
 					  udf_get_block);
 		if (err)
 			return err;
+		truncate_setsize(inode, newsize);
 		down_write(&iinfo->i_data_sem);
 		udf_clear_extent_cache(inode);
-		truncate_setsize(inode, newsize);
 		udf_truncate_extents(inode);
 		up_write(&iinfo->i_data_sem);
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/f2fs-don-t-clear-sgid-when-inheriting-acls.patch queue-4.9/ext2-don-t-clear-sgid-when-inheriting-acls.patch queue-4.9/hfsplus-don-t-clear-sgid-when-inheriting-acls.patch queue-4.9/btrfs-don-t-clear-sgid-when-inheriting-acls.patch queue-4.9/xfs-don-t-clear-sgid-when-inheriting-acls.patch queue-4.9/udf-fix-deadlock-between-writeback-and-udf_setsize.patch