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Date: Wed, 15 Jun 2022 12:03:41 +0800
From: yebin <yebin10@...wei.com>
To: Eric Whitney <enwlinux@...il.com>
CC: <tytso@....edu>, <adilger.kernel@...ger.ca>,
<linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<jack@...e.cz>
Subject: Re: [PATCH -next] ext4: Fix warning in ext4_da_release_space
On 2022/6/15 8:53, Eric Whitney wrote:
> * yebin <yebin10@...wei.com>:
>> ping...
>>
>> On 2022/5/20 10:55, Ye Bin wrote:
>>> We got issue as follows:
>>> WARNING: CPU: 2 PID: 1936 at fs/ext4/inode.c:1511 ext4_da_release_space+0x1b9/0x266
>>> Modules linked in:
>>> CPU: 2 PID: 1936 Comm: dd Not tainted 5.10.0+ #344
>>> RIP: 0010:ext4_da_release_space+0x1b9/0x266
>>> RSP: 0018:ffff888127307848 EFLAGS: 00010292
>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff843f67cc
>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffed1024e60ed9
>>> RBP: ffff888124dc8140 R08: 0000000000000083 R09: ffffed1075da6d23
>>> R10: ffff8883aed36917 R11: ffffed1075da6d22 R12: ffff888124dc83f0
>>> R13: ffff888124dc844c R14: ffff888124dc8168 R15: 000000000000000c
>>> FS: 00007f6b7247d740(0000) GS:ffff8883aed00000(0000) knlGS:0000000000000000
>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 00007ffc1a0b7dd8 CR3: 00000001065ce000 CR4: 00000000000006e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> Call Trace:
>>> ext4_es_remove_extent+0x187/0x230
>>> mpage_release_unused_pages+0x3af/0x470
>>> ext4_writepages+0xb9b/0x1160
>>> do_writepages+0xbb/0x1e0
>>> __filemap_fdatawrite_range+0x1b1/0x1f0
>>> file_write_and_wait_range+0x80/0xe0
>>> ext4_sync_file+0x13d/0x800
>>> vfs_fsync_range+0x75/0x140
>>> do_fsync+0x4d/0x90
>>> __x64_sys_fsync+0x1d/0x30
>>> do_syscall_64+0x33/0x40
>>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>
>>> Above issue may happens as follows:
>>> process1 process2
>>> ext4_da_write_begin
>>> ext4_da_reserve_space
>>> ext4_es_insert_delayed_block[1/1]
>>> ext4_da_write_begin
>>> ext4_es_insert_delayed_block[0/1]
>>> ext4_writepages
>>> ****Delayed block allocation failed****
>>> mpage_release_unused_pages
>>> ext4_es_remove_extent[1/1]
>>> ext4_da_release_space [reserved 0]
>>>
>>> ext4_da_write_begin
>>> ext4_es_scan_clu(inode, &ext4_es_is_delonly, lblk)
>>> ->As there exist [0, 1] extent, so will return true
>>> ext4_writepages
>>> ****Delayed block allocation failed****
>>> mpage_release_unused_pages
>>> ext4_es_remove_extent[0/1]
>>> ext4_da_release_space [reserved 1]
>>> ei->i_reserved_data_blocks [1->0]
>>>
>>> ext4_es_insert_delayed_block[1/1]
>>>
>>> ext4_writepages
>>> ****Delayed block allocation failed****
>>> mpage_release_unused_pages
>>> ext4_es_remove_extent[1/1]
>>> ext4_da_release_space [reserved 1]
>>> ei->i_reserved_data_blocks[0, -1]
>>> ->As ei->i_reserved_data_blocks already is zero but to_free is 1,
>>> will trigger warning.
>>>
>>> To solve above issue, introduce i_clu_lock to protect insert delayed
>>> block and remove block under cluster delay allocate mode.
>>>
>>> Signed-off-by: Ye Bin <yebin10@...wei.com>
>>> ---
>>> fs/ext4/ext4.h | 3 +++
>>> fs/ext4/extents_status.c | 5 +++++
>>> fs/ext4/inode.c | 11 +++++++++--
>>> fs/ext4/super.c | 1 +
>>> 4 files changed, 18 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>> index bcd3b9bf8069..47c88ac4d4a8 100644
>>> --- a/fs/ext4/ext4.h
>>> +++ b/fs/ext4/ext4.h
>>> @@ -1169,6 +1169,9 @@ struct ext4_inode_info {
>>> __u32 i_csum_seed;
>>> kprojid_t i_projid;
>>> +
>>> + /* Protect concurrent add cluster delayed block and remove block */
>>> + struct mutex i_clu_lock;
>>> };
>>> /*
>>> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
>>> index 9a3a8996aacf..dd679014db98 100644
>>> --- a/fs/ext4/extents_status.c
>>> +++ b/fs/ext4/extents_status.c
>>> @@ -1433,6 +1433,7 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>>> int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>>> ext4_lblk_t len)
>>> {
>>> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>> ext4_lblk_t end;
>>> int err = 0;
>>> int reserved = 0;
>>> @@ -1455,9 +1456,13 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>>> * so that we are sure __es_shrink() is done with the inode before it
>>> * is reclaimed.
>>> */
>>> + if (sbi->s_cluster_ratio != 1)
>>> + mutex_lock(&EXT4_I(inode)->i_clu_lock);
>>> write_lock(&EXT4_I(inode)->i_es_lock);
>>> err = __es_remove_extent(inode, lblk, end, &reserved);
>>> write_unlock(&EXT4_I(inode)->i_es_lock);
>>> + if (sbi->s_cluster_ratio != 1)
>>> + mutex_unlock(&EXT4_I(inode)->i_clu_lock);
>>> ext4_es_print_tree(inode);
>>> ext4_da_release_space(inode, reserved);
>>> return err;
>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>> index 01c9e4f743ba..1109d77ad60b 100644
>>> --- a/fs/ext4/inode.c
>>> +++ b/fs/ext4/inode.c
>>> @@ -1649,17 +1649,22 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>> goto errout;
>>> reserved = true;
>>> } else { /* bigalloc */
>>> + mutex_lock(&EXT4_I(inode)->i_clu_lock);
>>> if (!ext4_es_scan_clu(inode, &ext4_es_is_delonly, lblk)) {
>>> if (!ext4_es_scan_clu(inode,
>>> &ext4_es_is_mapped, lblk)) {
>>> ret = ext4_clu_mapped(inode,
>>> EXT4_B2C(sbi, lblk));
>>> - if (ret < 0)
>>> + if (ret < 0) {
>>> + mutex_unlock(&EXT4_I(inode)->i_clu_lock);
>>> goto errout;
>>> + }
>>> if (ret == 0) {
>>> ret = ext4_da_reserve_space(inode);
>>> - if (ret != 0) /* ENOSPC */
>>> + if (ret != 0) { /* ENOSPC */
>>> + mutex_unlock(&EXT4_I(inode)->i_clu_lock);
>>> goto errout;
>>> + }
>>> reserved = true;
>>> } else {
>>> allocated = true;
>>> @@ -1671,6 +1676,8 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>> }
>>> ret = ext4_es_insert_delayed_block(inode, lblk, allocated);
>>> + if (sbi->s_cluster_ratio != 1)
>>> + mutex_unlock(&EXT4_I(inode)->i_clu_lock);
>>> if (ret && reserved)
>>> ext4_da_release_space(inode, 1);
>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>> index c5021ca0a28a..aa6f2a68bf41 100644
>>> --- a/fs/ext4/super.c
>>> +++ b/fs/ext4/super.c
>>> @@ -1347,6 +1347,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
>>> INIT_WORK(&ei->i_rsv_conversion_work, ext4_end_io_rsv_work);
>>> ext4_fc_init_inode(&ei->vfs_inode);
>>> mutex_init(&ei->i_fc_lock);
>>> + mutex_init(&ei->i_clu_lock);
>>> return &ei->vfs_inode;
>>> }
> As you have reported, it looks like there is potential for a race between
> mpage_release_unused_pages and ext4_insert_delayed_block when running on a
> bigalloc file system in rare circumstances. There should have been locking
> in mpage_release_unused_pages to avoid this. The locking was missed when new
> code was added to ext4_insert_delayed_block to handle bigalloc delayed block
> accounting.
>
> I have a solution that addresses that omission and is simpler than your
> proposed fix. It does not require adding a new lock. I'm putting that
> patch through the usual testing cycles, plus new stress testing to verify that
> no lock dependency problems exist. It looks good so far, and I expect to post
> it tomorrow. If you would be willing to test that patch, we would welcome
> it. As you have not chosen to explain how you've triggered the race, you
> are in a better position to determine whether the patch will successfully
> address it.
I've provided a way to reproduce.
> It's important to understand that the delayed block allocation failures
> you have noted in your call graphs are far more important events than the
> block accounting errors that occur due to the race. The delayed block
> allocation failures represent data loss for the user, and they should really
> never happen. That's why we'd like to understand how you triggered the race,
> whether by fuzzing or some other method. Depending on what was done, there
> may be a need to harden the code.
>
> Eric
> .
>
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