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authorJan Kara <jack@suse.com>2015-12-07 14:28:03 -0500
committerTheodore Ts'o <tytso@mit.edu>2015-12-07 14:28:03 -0500
commitea3d7209ca01da209cda6f0dea8be9cc4b7a933b (patch)
tree809b37322befdf8dda2d12b991d1c832241bc8bc /fs/ext4/extents.c
parentf41683a204ea61568f0fd0804d47c19561f2ee39 (diff)
ext4: fix races between page faults and hole punching
Currently, page faults and hole punching are completely unsynchronized. This can result in page fault faulting in a page into a range that we are punching after truncate_pagecache_range() has been called and thus we can end up with a page mapped to disk blocks that will be shortly freed. Filesystem corruption will shortly follow. Note that the same race is avoided for truncate by checking page fault offset against i_size but there isn't similar mechanism available for punching holes. Fix the problem by creating new rw semaphore i_mmap_sem in inode and grab it for writing over truncate, hole punching, and other functions removing blocks from extent tree and for read over page faults. We cannot easily use i_data_sem for this since that ranks below transaction start and we need something ranking above it so that it can be held over the whole truncate / hole punching operation. Also remove various workarounds we had in the code to reduce race window when page fault could have created pages with stale mapping information. Signed-off-by: Jan Kara <jack@suse.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'fs/ext4/extents.c')
-rw-r--r--fs/ext4/extents.c54
1 files changed, 30 insertions, 24 deletions
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 551353b1b17a..5be9ca5a8a7a 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4770,7 +4770,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
int partial_begin, partial_end;
loff_t start, end;
ext4_lblk_t lblk;
- struct address_space *mapping = inode->i_mapping;
unsigned int blkbits = inode->i_blkbits;
trace_ext4_zero_range(inode, offset, len, mode);
@@ -4786,17 +4785,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
}
/*
- * Write out all dirty pages to avoid race conditions
- * Then release them.
- */
- if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
- ret = filemap_write_and_wait_range(mapping, offset,
- offset + len - 1);
- if (ret)
- return ret;
- }
-
- /*
* Round up offset. This is not fallocate, we neet to zero out
* blocks, so convert interior block aligned part of the range to
* unwritten and possibly manually zero out unaligned parts of the
@@ -4856,16 +4844,22 @@ static long ext4_zero_range(struct file *file, loff_t offset,
flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
EXT4_EX_NOCACHE);
- /* Now release the pages and zero block aligned part of pages*/
- truncate_pagecache_range(inode, start, end - 1);
- inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
-
/* 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.
+ */
+ down_write(&EXT4_I(inode)->i_mmap_sem);
+ /* Now release the pages and zero block aligned part of pages */
+ truncate_pagecache_range(inode, start, end - 1);
+ inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
+
ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
flags, mode);
+ up_write(&EXT4_I(inode)->i_mmap_sem);
if (ret)
goto out_dio;
}
@@ -5524,17 +5518,22 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
goto out_mutex;
}
- truncate_pagecache(inode, ioffset);
-
/* Wait for existing dio to complete */
ext4_inode_block_unlocked_dio(inode);
inode_dio_wait(inode);
+ /*
+ * Prevent page faults from reinstantiating pages we have released from
+ * page cache.
+ */
+ down_write(&EXT4_I(inode)->i_mmap_sem);
+ truncate_pagecache(inode, ioffset);
+
credits = ext4_writepage_trans_blocks(inode);
handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
- goto out_dio;
+ goto out_mmap;
}
down_write(&EXT4_I(inode)->i_data_sem);
@@ -5573,7 +5572,8 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
out_stop:
ext4_journal_stop(handle);
-out_dio:
+out_mmap:
+ up_write(&EXT4_I(inode)->i_mmap_sem);
ext4_inode_resume_unlocked_dio(inode);
out_mutex:
mutex_unlock(&inode->i_mutex);
@@ -5660,17 +5660,22 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
goto out_mutex;
}
- truncate_pagecache(inode, ioffset);
-
/* Wait for existing dio to complete */
ext4_inode_block_unlocked_dio(inode);
inode_dio_wait(inode);
+ /*
+ * Prevent page faults from reinstantiating pages we have released from
+ * page cache.
+ */
+ down_write(&EXT4_I(inode)->i_mmap_sem);
+ truncate_pagecache(inode, ioffset);
+
credits = ext4_writepage_trans_blocks(inode);
handle = ext4_journal_start(inode, EXT4_HT_TRUNCATE, credits);
if (IS_ERR(handle)) {
ret = PTR_ERR(handle);
- goto out_dio;
+ goto out_mmap;
}
/* Expand file to avoid data loss if there is error while shifting */
@@ -5741,7 +5746,8 @@ int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
out_stop:
ext4_journal_stop(handle);
-out_dio:
+out_mmap:
+ up_write(&EXT4_I(inode)->i_mmap_sem);
ext4_inode_resume_unlocked_dio(inode);
out_mutex:
mutex_unlock(&inode->i_mutex);