linux-kernel - Re: [PATCH -next] ext4: fix warning in ext4_handle_inode

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Date:   Tue, 29 Mar 2022 12:11:33 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     yebin <yebin10@...wei.com>
Cc:     <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <jack@...e.cz>, <lczerner@...hat.com>
Subject: Re: [PATCH -next] ext4: fix warning in ext4_handle_inode_extension

yebin <yebin10@...wei.com> writes:

> On 2022/3/28 23:57, Gabriel Krisman Bertazi wrote:
>> Ye Bin <yebin10@...wei.com> writes:
>>
>>> 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@...wei.com>
>>> ---
>>>   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;
>> Shouldn't this always be done if ext4_mark_inode_dirty fails?
>>
>> if (rc)
>>      EXT4_I(inode)->i_disksize = old_disksize;
>>
>> Otherwise you hit the same issue if (!error && rc), no?
>
> In fact, '(!error && rc)' condition is always unsatisfied.
>
> ext4_setattr
> ...
> down_write(&EXT4_I(inode)->i_data_sem);
> EXT4_I(inode)->i_disksize = attr->ia_size;
> rc = ext4_mark_inode_dirty(handle, inode);
> *if (!error) **
> **        error = rc;*

Oh right. sorry for the noise.

-- 
Gabriel Krisman Bertazi