Patch "ext4: move unlocked dio protection from ext4_alloc_file_blocks()" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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

    ext4: move unlocked dio protection from ext4_alloc_file_blocks()

to the 4.4-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-move-unlocked-dio-protection-from-ext4_alloc_file_blocks.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 17048e8a083fec7ad841d88ef0812707fbc7e39f Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.com>
Date: Mon, 7 Dec 2015 14:29:17 -0500
Subject: ext4: move unlocked dio protection from ext4_alloc_file_blocks()

From: Jan Kara <jack@suse.com>

commit 17048e8a083fec7ad841d88ef0812707fbc7e39f upstream.

Currently ext4_alloc_file_blocks() was handling protection against
unlocked DIO. However we now need to sometimes call it under i_mmap_sem
and sometimes not and DIO protection ranks above it (although strictly
speaking this cannot currently create any deadlocks). Also
ext4_zero_range() was actually getting & releasing unlocked DIO
protection twice in some cases. Luckily it didn't introduce any real bug
but it was a land mine waiting to be stepped on.  So move DIO protection
out from ext4_alloc_file_blocks() into the two callsites.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext4/extents.c |   21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4685,10 +4685,6 @@ static int ext4_alloc_file_blocks(struct
 	if (len <= EXT_UNWRITTEN_MAX_LEN)
 		flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
 
-	/* Wait all existing dio workers, newcomers will block on i_mutex */
-	ext4_inode_block_unlocked_dio(inode);
-	inode_dio_wait(inode);
-
 	/*
 	 * credits to insert 1 extent into extent tree
 	 */
@@ -4752,8 +4748,6 @@ retry:
 		goto retry;
 	}
 
-	ext4_inode_resume_unlocked_dio(inode);
-
 	return ret > 0 ? ret2 : ret;
 }
 
@@ -4827,6 +4821,10 @@ static long ext4_zero_range(struct file
 	if (mode & FALLOC_FL_KEEP_SIZE)
 		flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
 
+	/* Wait all existing dio workers, newcomers will block on i_mutex */
+	ext4_inode_block_unlocked_dio(inode);
+	inode_dio_wait(inode);
+
 	/* Preallocate the range including the unaligned edges */
 	if (partial_begin || partial_end) {
 		ret = ext4_alloc_file_blocks(file,
@@ -4835,7 +4833,7 @@ static long ext4_zero_range(struct file
 				 round_down(offset, 1 << blkbits)) >> blkbits,
 				new_size, flags, mode);
 		if (ret)
-			goto out_mutex;
+			goto out_dio;
 
 	}
 
@@ -4844,10 +4842,6 @@ static long ext4_zero_range(struct file
 		flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
 			  EXT4_EX_NOCACHE);
 
-		/* Wait all existing dio workers, newcomers will block on i_mutex */
-		ext4_inode_block_unlocked_dio(inode);
-		inode_dio_wait(inode);
-
 		/*
 		 * Prevent page faults from reinstantiating pages we have
 		 * released from page cache.
@@ -4992,8 +4986,13 @@ long ext4_fallocate(struct file *file, i
 			goto out;
 	}
 
+	/* Wait all existing dio workers, newcomers will block on i_mutex */
+	ext4_inode_block_unlocked_dio(inode);
+	inode_dio_wait(inode);
+
 	ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
 				     flags, mode);
+	ext4_inode_resume_unlocked_dio(inode);
 	if (ret)
 		goto out;
 


Patches currently in stable-queue which might be from jack@suse.com are

queue-4.4/ext4-fix-races-between-page-faults-and-hole-punching.patch
queue-4.4/ext4-move-unlocked-dio-protection-from-ext4_alloc_file_blocks.patch
queue-4.4/ext4-fix-races-between-buffered-io-and-collapse-insert-range.patch
queue-4.4/ext4-fix-races-of-writeback-with-punch-hole-and-zero-range.patch