On Wed 18-11-15 01:39:37, Elliott, Robert (Persistent Memory) wrote:
>
> > -----Original Message-----
> > From: linux-ext4-owner@xxxxxxxxxxxxxxx [mailto:linux-ext4-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Jan Kara
> > Sent: Tuesday, November 10, 2015 1:51 PM
> > Subject: [PATCH 3/9] ext4: Fix races between buffered IO and collapse /
> > insert range
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > /*
> > - * Prevent page faults from reinstantiating pages we have released from
> > + * Prevent page faults from reinstantiating we have released from
> > * page cache.
>
> I don't think you meant to delete that word...
Right. Thanks for catching that. Attached is a fixed version of the patch.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
>From f01b71d438aa8c3dc4c8eeb54c82595ecd93c5c3 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxxx>
Date: Fri, 16 Oct 2015 13:55:06 +0200
Subject: [PATCH] ext4: Fix races between buffered IO and collapse / insert
range
Current code implementing FALLOC_FL_COLLAPSE_RANGE and
FALLOC_FL_INSERT_RANGE is prone to races with buffered writes and page
faults. If buffered write or write via mmap manages to squeeze between
filemap_write_and_wait_range() and truncate_pagecache() in the fallocate
implementations, the written data is simply discarded by
truncate_pagecache() although it should have been shifted.
Fix the problem by moving filemap_write_and_wait_range() call inside
i_mutex and i_mmap_sem. That way we are protected against races with
both buffered writes and page faults.
Signed-off-by: Jan Kara <jack@xxxxxxxx>
---
fs/ext4/extents.c | 59 +++++++++++++++++++++++++++++--------------------------
1 file changed, 31 insertions(+), 28 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 65b5ada2833f..4b105c96df08 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5487,21 +5487,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
return ret;
}
- /*
- * Need to round down offset to be aligned with page size boundary
- * for page size > block size.
- */
- ioffset = round_down(offset, PAGE_SIZE);
-
- /* Write out all dirty pages */
- ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
- LLONG_MAX);
- if (ret)
- return ret;
-
- /* Take mutex lock */
mutex_lock(&inode->i_mutex);
-
/*
* There is no need to overlap collapse range with EOF, in which case
* it is effectively a truncate operation
@@ -5526,6 +5512,27 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
* page cache.
*/
down_write(&EXT4_I(inode)->i_mmap_sem);
+ /*
+ * Need to round down offset to be aligned with page size boundary
+ * for page size > block size.
+ */
+ ioffset = round_down(offset, PAGE_SIZE);
+ /*
+ * Write tail of the last page before removed range since it will get
+ * removed from the page cache below.
+ */
+ ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, offset);
+ if (ret)
+ goto out_mmap;
+ /*
+ * Write data that will be shifted to preserve them when discarding
+ * page cache below. We are also protected from pages becoming dirty
+ * by i_mmap_sem.
+ */
+ ret = filemap_write_and_wait_range(inode->i_mapping, offset + len,
+ LLONG_MAX);
+ if (ret)
+ goto out_mmap;
truncate_pagecache(inode, ioffset);
credits = ext4_writepage_trans_blocks(inode);
@@ -5626,21 +5633,7 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
return ret;
}
- /*
- * Need to round down to align start offset to page size boundary
- * for page size > block size.
- */
- ioffset = round_down(offset, PAGE_SIZE);
-
- /* Write out all dirty pages */
- ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
- LLONG_MAX);
- if (ret)
- return ret;
-
- /* Take mutex lock */
mutex_lock(&inode->i_mutex);
-
/* Currently just for extent based files */
if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
ret = -EOPNOTSUPP;
@@ -5668,6 +5661,16 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
* page cache.
*/
down_write(&EXT4_I(inode)->i_mmap_sem);
+ /*
+ * Need to round down to align start offset to page size boundary
+ * for page size > block size.
+ */
+ ioffset = round_down(offset, PAGE_SIZE);
+ /* Write out all dirty pages */
+ ret = filemap_write_and_wait_range(inode->i_mapping, ioffset,
+ LLONG_MAX);
+ if (ret)
+ goto out_mmap;
truncate_pagecache(inode, ioffset);
credits = ext4_writepage_trans_blocks(inode);
--
2.1.4
