Re: [PATCH -next] ext4: fix warning in ext4_handle_inode_extension
From: yebin
Date: Wed Apr 13 2022 - 22:46:45 EST
On 2022/3/30 21:30, Jan Kara wrote:
On Wed 30-03-22 20:08:13, yebin wrote:
On 2022/3/29 17:28, Jan Kara wrote:
On Sat 26-03-22 14:53:51, Ye Bin wrote:
We got issue as follows:
EXT4-fs error (device loop0) in ext4_reserve_inode_write:5741: Out of memory
EXT4-fs error (device loop0): ext4_setattr:5462: inode #13: comm syz-executor.0: mark_inode_dirty error
EXT4-fs error (device loop0) in ext4_setattr:5519: Out of memory
EXT4-fs error (device loop0): ext4_ind_map_blocks:595: inode #13: comm syz-executor.0: Can't allocate blocks for non-extent mapped inodes with bigalloc
------------[ cut here ]------------
WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_file_write_iter+0x11c9/0x1220
Modules linked in:
CPU: 1 PID: 4361 Comm: syz-executor.0 Not tainted 5.10.0+ #1
RIP: 0010:ext4_file_write_iter+0x11c9/0x1220
RSP: 0018:ffff924d80b27c00 EFLAGS: 00010282
RAX: ffffffff815a3379 RBX: 0000000000000000 RCX: 000000003b000000
RDX: ffff924d81601000 RSI: 00000000000009cc RDI: 00000000000009cd
RBP: 000000000000000d R08: ffffffffbc5a2c6b R09: 0000902e0e52a96f
R10: ffff902e2b7c1b40 R11: ffff902e2b7c1b40 R12: 000000000000000a
R13: 0000000000000001 R14: ffff902e0e52aa10 R15: ffffffffffffff8b
FS: 00007f81a7f65700(0000) GS:ffff902e3bc80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 000000012db88001 CR4: 00000000003706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
do_iter_readv_writev+0x2e5/0x360
do_iter_write+0x112/0x4c0
do_pwritev+0x1e5/0x390
__x64_sys_pwritev2+0x7e/0xa0
do_syscall_64+0x37/0x50
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Above issue may happen as follows:
Assume
inode.i_size=4096
EXT4_I(inode)->i_disksize=4096
step 1: set inode->i_isize = 8192
ext4_setattr
if (attr->ia_size != inode->i_size)
EXT4_I(inode)->i_disksize = attr->ia_size;
rc = ext4_mark_inode_dirty
ext4_reserve_inode_write
ext4_get_inode_loc
__ext4_get_inode_loc
sb_getblk --> return -ENOMEM
...
if (!error) ->will not update i_size
i_size_write(inode, attr->ia_size);
Now:
inode.i_size=4096
EXT4_I(inode)->i_disksize=8192
step 2: Direct write 4096 bytes
ext4_file_write_iter
ext4_dio_write_iter
iomap_dio_rw ->return error
if (extend)
ext4_handle_inode_extension
WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);
->Then trigger warning.
To solve above issue, if mark inode dirty failed in ext4_setattr just
set 'EXT4_I(inode)->i_disksize' with old value.
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
Thanks for the fix! So I think this deserves a further debate. I have two
points here:
1) If ext4_mark_inode_dirty() fails (or basically any metadata writeback)
we must abort the journal because metadata is not guaranteed to be
consistent anymore. In this particular callsite of ext4_mark_inode_dirty()
you were able to undo the changes but there are many more where it is not
sanely possible AFAICT. Hence I think that ext4_reserve_inode_write() needs
to call ext4_journal_abort_handle() (as already happens inside
__ext4_journal_get_write_access()) and not just ext4_std_error().
2) The assertion in ext4_handle_inode_extension() should be conditioned on
!is_journal_aborted() to avoid useless warnings for filesystems we know are
inconsistent anyway.
Thoughts?
Honza
Do you mean call jbd2_abort in ext4_reserve_inode_write() ?
Yes.
If we abort journal when metadata is not guaranteed to be consistent. The
mode of ‘errors=continue’ is unnecessary.
Well, firstly, errors=continue was always the best effort. There are no
guarantees which failures we are able to withstand and which not.
Generally, I think we try to withstand on-disk filesystem inconsistency but
not inconsistency coming from programming errors or other external factors
like out-of-memory conditions. Secondly, we already do abort the journal
when e.g. jbd2_journal_get_write_access() fails (although that generally
means some internal inconsistency) or when say revoke handling fails to
allocate memory for a revoke record. So it won't be a new thing. Thirdly,
and perhaps most importantly, you have found and fixed just one fairly
innocent problem happening due to in memory inode state getting
inconsistent after we fail to record the inode in the journal. There are
almost 80 callsites of ext4_mark_inode_dirty() and honestly I suspect that
e.g. inconsistent states resulting from extent tree manipulations being
aborted in the middle due to ext4_ext_dirty() failing due to ENOMEM will
also trigger all sorts of "interesting" behavior. So that's why I'd rather
abort the journal than try to continue when we almost certainly now we
cannot.
One other possibility I could see dealing with this class of problems is
using __GFP_NOFAIL for inode buffer head allocation (through
sb_getblk_gfp()) in __ext4_get_inode_loc(). BTW, how did you trigger NULL
sb_getblk() return in the first place? AFAICS grow_buffers() already uses
__GFP_NOFAIL for all the allocations?
Honza
To be honest, I don't know syzkaller how to inject the NOMEM fault. If
syzkaller
rely on the memory fault injection mode provided by the kernel, should
report
null pointer access. Anyway, If inject a single point of IO fault, we
still have to
face the same situation.
---
fs/ext4/inode.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 90fd6f7b6209..8adf1f802f6c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5384,6 +5384,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
if (attr->ia_valid & ATTR_SIZE) {
handle_t *handle;
loff_t oldsize = inode->i_size;
+ loff_t old_disksize;
int shrink = (attr->ia_size < inode->i_size);
if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
@@ -5455,6 +5456,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
inode->i_sb->s_blocksize_bits);
down_write(&EXT4_I(inode)->i_data_sem);
+ old_disksize = EXT4_I(inode)->i_disksize;
EXT4_I(inode)->i_disksize = attr->ia_size;
rc = ext4_mark_inode_dirty(handle, inode);
if (!error)
@@ -5466,6 +5468,8 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
*/
if (!error)
i_size_write(inode, attr->ia_size);
+ else
+ EXT4_I(inode)->i_disksize = old_disksize;
up_write(&EXT4_I(inode)->i_data_sem);
ext4_journal_stop(handle);
if (error)
--
2.31.1