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authorJan Kara <jack@suse.com>2015-12-07 14:31:11 -0500
committerTheodore Ts'o <tytso@mit.edu>2015-12-07 14:31:11 -0500
commit32ebffd3bbb4162da5ff88f9a35dd32d0a28ea70 (patch)
tree11d7854acb61128821b948796d1eb2e2f87b925f
parent17048e8a083fec7ad841d88ef0812707fbc7e39f (diff)
downloadop-kernel-dev-32ebffd3bbb4162da5ff88f9a35dd32d0a28ea70.zip
op-kernel-dev-32ebffd3bbb4162da5ff88f9a35dd32d0a28ea70.tar.gz
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@suse.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
-rw-r--r--fs/ext4/extents.c59
1 files changed, 31 insertions, 28 deletions
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 65b5ada..4b105c9 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);
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