[PATCH 3.2 12/74] udf: Fix deadlock between writeback and udf_setsize()

[Ben Hutchings]

3.2.94-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Jan Kara <j...@suse.cz>

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.

Fixes: 7e49b6f2480cb9a9e7322a91592e56a5c85361f5
Signed-off-by: Jan Kara <j...@suse.cz>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 fs/udf/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1145,8 +1145,8 @@ int udf_setsize(struct inode *inode, lof
                        up_write(&iinfo->i_data_sem);
                        return err;
                }
-               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);
@@ -1162,8 +1162,8 @@ int udf_setsize(struct inode *inode, lof
                                          udf_get_block);
                if (err)
                        return err;
-               down_write(&iinfo->i_data_sem);
                truncate_setsize(inode, newsize);
+               down_write(&iinfo->i_data_sem);
                udf_truncate_extents(inode);
                up_write(&iinfo->i_data_sem);
        }