[PATCH 3.16 093/134] ext4: evict inline data when writing to memory map

Ben Hutchings
2017-08-18T13:15:52Z

From: Eric Biggers <ebiggers@google.com>

commit 7b4cc9787fe35b3ee2dfb1c35e22eafc32e00c33 upstream.

Currently the case of writing via mmap to a file with inline data is not
handled. This is maybe a rare case since it requires a writable memory
map of a very small file, but it is trivial to trigger with on
inline_data filesystem, and it causes the
'BUG_ON(ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA));' in
ext4_writepages() to be hit:

mkfs.ext4 -O inline_data /dev/vdb
mount /dev/vdb /mnt
xfs_io -f /mnt/file \
-c 'pwrite 0 1' \
-c 'mmap -w 0 1m' \
-c 'mwrite 0 1' \
-c 'fsync'

kernel BUG at fs/ext4/inode.c:2723!
invalid opcode: 0000 [#1] SMP
CPU: 1 PID: 2532 Comm: xfs_io Not tainted 4.11.0-rc1-xfstests-00301-g071d9acf3d1f #633
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-20170228_101828-anatol 04/01/2014
task: ffff88003d3a8040 task.stack: ffffc90000300000
RIP: 0010:ext4_writepages+0xc89/0xf8a
RSP: 0018:ffffc90000303ca0 EFLAGS: 00010283
RAX: 0000028410000000 RBX: ffff8800383fa3b0 RCX: ffffffff812afcdc
RDX: 00000a9d00000246 RSI: ffffffff81e660e0 RDI: 0000000000000246
RBP: ffffc90000303dc0 R08: 0000000000000002 R09: 869618e8f99b4fa5
R10: 00000000852287a2 R11: 00000000a03b49f4 R12: ffff88003808e698
R13: 0000000000000000 R14: 7fffffffffffffff R15: 7fffffffffffffff
FS: 00007fd3e53094c0(0000) GS:ffff88003e400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd3e4c51000 CR3: 000000003d554000 CR4: 00000000003406e0
Call Trace:
? _raw_spin_unlock+0x27/0x2a
? kvm_clock_read+0x1e/0x20
do_writepages+0x23/0x2c
? do_writepages+0x23/0x2c
__filemap_fdatawrite_range+0x80/0x87
filemap_write_and_wait_range+0x67/0x8c
ext4_sync_file+0x20e/0x472
vfs_fsync_range+0x8e/0x9f
? syscall_trace_enter+0x25b/0x2d0
vfs_fsync+0x1c/0x1e
do_fsync+0x31/0x4a
SyS_fsync+0x10/0x14
do_syscall_64+0x69/0x131
entry_SYSCALL64_slow_path+0x25/0x25

We could try to be smart and keep the inline data in this case, or at
least support delayed allocation when allocating the block, but these
solutions would be more complicated and don't seem worthwhile given how
rare this case seems to be. So just fix the bug by calling
ext4_convert_inline_data() when we're asked to make a page writable, so
that any inline data gets evicted, with the block allocated immediately.

Reported-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/inode.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5273,6 +5273,11 @@ int ext4_page_mkwrite(struct vm_area_str

sb_start_pagefault(inode->i_sb);
file_update_time(vma->vm_file);
+
+ ret = ext4_convert_inline_data(inode);
+ if (ret)
+ goto out_ret;
+
/* Delalloc case is easy... */
if (test_opt(inode->i_sb, DELALLOC) &&
!ext4_should_journal_data(inode) &&