linux-ext4 - [PATCH 08/11] ext4: Convert DAX faults to iomap infrastructure

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Date:   Tue,  8 Nov 2016 12:08:14 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ted Tso <tytso@....edu>
Cc:     <linux-ext4@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH 08/11] ext4: Convert DAX faults to iomap infrastructure

Convert DAX faults to use iomap infrastructure. We would not have to start
transaction in ext4_dax_fault() anymore since ext4_iomap_begin takes
care of that but so far we do that to avoid lock inversion of
transaction start with DAX entry lock which gets acquired in
dax_iomap_fault() before calling ->iomap_begin handler.

Signed-off-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/file.c  |  9 +++++----
 fs/ext4/inode.c | 14 +++++++++-----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 1953fe34f9fe..b5f184493c57 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -275,7 +275,7 @@ static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	if (IS_ERR(handle))
 		result = VM_FAULT_SIGBUS;
 	else
-		result = dax_fault(vma, vmf, ext4_dax_get_block);
+		result = dax_iomap_fault(vma, vmf, &ext4_iomap_ops);
 
 	if (write) {
 		if (!IS_ERR(handle))
@@ -309,9 +309,10 @@ static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
 
 	if (IS_ERR(handle))
 		result = VM_FAULT_SIGBUS;
-	else
-		result = dax_pmd_fault(vma, addr, pmd, flags,
-					 ext4_dax_get_block);
+	else {
+		result = dax_iomap_pmd_fault(vma, addr, pmd, flags,
+					     &ext4_iomap_ops);
+	}
 
 	if (write) {
 		if (!IS_ERR(handle))
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3192ec0768d4..4d71c7bc3524 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3361,12 +3361,16 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		}
 
 		/*
-		 * If we added blocks beyond i_size we need to make sure they
+		 * If we added blocks beyond i_size, we need to make sure they
 		 * will get truncated if we crash before updating i_size in
-		 * ext4_iomap_end().
+		 * ext4_iomap_end(). For faults we don't need to do that (and
+		 * even cannot because for orphan list operations inode_lock is
+		 * required) - if we happen to instantiate block beyond i_size,
+		 * it is because we race with truncate which has already added
+		 * the inode to the orphan list.
 		 */
-		if (first_block + map.m_len >
-		    (inode->i_size + (1 << blkbits) - 1) >> blkbits) {
+		if (!(flags & IOMAP_FAULT) && first_block + map.m_len >
+		    (i_size_read(inode) + (1 << blkbits) - 1) >> blkbits) {
 			int err;
 
 			err = ext4_orphan_add(handle, inode);
@@ -3412,7 +3416,7 @@ static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
 	int blkbits = inode->i_blkbits;
 	bool truncate = false;
 
-	if (!(flags & IOMAP_WRITE))
+	if (!(flags & IOMAP_WRITE) || (flags & IOMAP_FAULT))
 		return 0;
 
 	handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
-- 
2.6.6

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