Patch "ext4: return to starting transaction in ext4_dax_huge_fault()" has been added to the 4.11-stable tree

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

ext4: return to starting transaction in ext4_dax_huge_fault()

to the 4.11-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:
ext4-return-to-starting-transaction-in-ext4_dax_huge_fault.patch
and it can be found in the queue-4.11 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: Fri, 12 May 2017 15:46:54 -0700
Subject: ext4: return to starting transaction in ext4_dax_huge_fault()

From: Jan Kara <[email protected]>

commit fb26a1cbed8c90025572d48bc9eabe59f7571e88 upstream.

DAX will return to locking exceptional entry before mapping blocks for a page fault to fix possible races with concurrent writes. To avoid lock inversion between exceptional entry lock and transaction start, start the transaction already in ext4_dax_huge_fault().

---
 fs/ext4/file.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

@@ -257,6 +257,7 @@ static int ext4_dax_huge_fault(struct vm
 		enum page_entry_size pe_size)
 {
 	int result;
+	handle_t *handle = NULL;
 	struct inode *inode = file_inode(vmf->vma->vm_file);
 	struct super_block *sb = inode->i_sb;
 	bool write = vmf->flags & FAULT_FLAG_WRITE;

@@ -264,12 +265,24 @@ static int ext4_dax_huge_fault(struct vm
 	if (write) {
 		sb_start_pagefault(sb);
 		file_update_time(vmf->vma->vm_file);
+		down_read(&EXT4_I(inode)->i_mmap_sem);
+		handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
+					       EXT4_DATA_TRANS_BLOCKS(sb));
+	} else {
+		down_read(&EXT4_I(inode)->i_mmap_sem);
 	}
-	down_read(&EXT4_I(inode)->i_mmap_sem);
-	result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops);
-	up_read(&EXT4_I(inode)->i_mmap_sem);
-	if (write)
+	if (!IS_ERR(handle))
+		result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops);
+	else
+		result = VM_FAULT_SIGBUS;
+	if (write) {
+		if (!IS_ERR(handle))
+			ext4_journal_stop(handle);
+		up_read(&EXT4_I(inode)->i_mmap_sem);
 		sb_end_pagefault(sb);
+	} else {
+		up_read(&EXT4_I(inode)->i_mmap_sem);
+	}
 
 	return result;
 }

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

queue-4.11/fs-block_dev-always-invalidate-cleancache-in-invalidate_bdev.patch queue-4.11/ext4-return-to-starting-transaction-in-ext4_dax_huge_fault.patch queue-4.11/dax-prevent-invalidation-of-mapped-dax-entries.patch queue-4.11/dax-fix-pmd-data-corruption-when-fault-races-with-write.patch queue-4.11/f2fs-make-flush-bios-explicitely-sync.patch queue-4.11/jbd2-fix-dbench4-performance-regression-for-nobarrier-mounts.patch queue-4.11/fs-fix-data-invalidation-in-the-cleancache-during-direct-io.patch queue-4.11/mm-fix-data-corruption-due-to-stale-mmap-reads.patch