| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <65b89566-1038-4422-9e2e-4d7da26dd1c7@kernel.org>
Date: Wed, 20 Nov 2024 11:26:44 +0800
From: Chao Yu <chao@...nel.org>
To: Zhiguo Niu <niuzhiguo84@...il.com>
Cc: Chao Yu <chao@...nel.org>, Xiuhong Wang <xiuhong.wang.cn@...il.com>,
Xiuhong Wang <xiuhong.wang@...soc.com>, jaegeuk@...nel.org,
linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
hao_hao.wang@...soc.com, ke.wang@...soc.com
Subject: Re: [PATCH] f2fs: Fix to avoid long time to shrink extent cache
On 2024/11/19 16:26, Zhiguo Niu wrote:
> Chao Yu <chao@...nel.org> 于2024年11月19日周二 15:50写道：
>>
>> On 2024/11/19 14:46, Xiuhong Wang wrote:
>>> Chao Yu <chao@...nel.org> 于2024年11月19日周二 14:05写道：
>>>>
>>>> On 2024/11/12 19:06, Xiuhong Wang wrote:
>>>>> We encountered a system hang problem based on the following
>>>>> experiment:
>>>>> There are 17 processes, 8 of which do 4k data read, write and
>>>>> compare tests, and 8 do 64k read, write and compare tests. Each
>>>>> thread writes a 256M file, and another thread writes a large file
>>>>> to 80% of the disk, and then keeps doing read operations, all of
>>>>> which are direct operations. This will cause the large file to be
>>>>> filled to 80% of the disk to be severely fragmented. On a 512GB
>>>>> device, this large file may generate a huge zombie extent tree.
>>>>>
>>>>> When system shutting down, the init process needs to wait for the
>>>>> writeback process, and the writeback process may encounter the
>>>>> situation where the READ_EXTENT_CACHE space is insufficient and
>>>>> needs to free the zombie extent tree. The extent tree has a large
>>>>> number of extent nodes, it will a long free time to free, which
>>>>> triggers system hang.
>>>> > > The stack when the problem occurs is as follows:
>>>>> crash_arm64> bt 1
>>>>> PID: 1 TASK: ffffff80801a9200 CPU: 1 COMMAND: "init"
>>>>> #0 [ffffffc00806b9a0] __switch_to at ffffffc00810711c
>>>>> #1 [ffffffc00806ba00] __schedule at ffffffc0097c1c4c
>>>>> #2 [ffffffc00806ba60] schedule at ffffffc0097c2308
>>>>> #3 [ffffffc00806bab0] wb_wait_for_completion at ffffffc0086320d4
>>>>> #4 [ffffffc00806bb20] writeback_inodes_sb at ffffffc00863719c
>>>>> #5 [ffffffc00806bba0] sync_filesystem at ffffffc00863c98c
>>>>> #6 [ffffffc00806bbc0] f2fs_quota_off_umount at ffffffc00886fc60
>>>>> #7 [ffffffc00806bc20] f2fs_put_super at ffffffc0088715b4
>>>>> #8 [ffffffc00806bc60] generic_shutdown_super at ffffffc0085cd61c
>>>>> #9 [ffffffc00806bcd0] kill_f2fs_super at ffffffc00886b3dc
>>>>>
>>>>> crash_arm64> bt 14997
>>>>> PID: 14997 TASK: ffffff8119d82400 CPU: 3 COMMAND: "kworker/u16:0"
>>>>> #0 [ffffffc019f8b760] __detach_extent_node at ffffffc0088d5a58
>>>>> #1 [ffffffc019f8b790] __release_extent_node at ffffffc0088d5970
>>>>> #2 [ffffffc019f8b810] f2fs_shrink_extent_tree at ffffffc0088d5c7c
>>>>> #3 [ffffffc019f8b8a0] f2fs_balance_fs_bg at ffffffc0088c109c
>>>>> #4 [ffffffc019f8b910] f2fs_write_node_pages at ffffffc0088bd4d8
>>>>> #5 [ffffffc019f8b990] do_writepages at ffffffc0084a0b5c
>>>>> #6 [ffffffc019f8b9f0] __writeback_single_inode at ffffffc00862ee28
>>>>> #7 [ffffffc019f8bb30] writeback_sb_inodes at ffffffc0086358c0
>>>>> #8 [ffffffc019f8bc10] wb_writeback at ffffffc0086362dc
>>>>> #9 [ffffffc019f8bcc0] wb_do_writeback at ffffffc008634910
>>>>>
>>>>> Process 14997 ran for too long and caused the system hang.
>>>>>
>>>>> At this time, there are still 1086911 extent nodes in this zombie
>>>>> extent tree that need to be cleaned up.
>>>>>
>>>>> crash_arm64_sprd_v8.0.3++> extent_tree.node_cnt ffffff80896cc500
>>>>> node_cnt = {
>>>>> counter = 1086911
>>>>> },
>>>>>
>>>>> The root cause of this problem is that when the f2fs_balance_fs
>>>>> function is called in the write process, it will determine
>>>>> whether to call f2fs_balance_fs_bg, but it is difficult to
>>>>> meet the condition of excess_cached_nats. When the
>>>>> f2fs_shrink_extent_tree function is called to free during
>>>>> f2fs_write_node_pages, there are too many extent nodes on the
>>>>> extent tree, which causes a loop and causes a system hang.
>>>>>
>>>>> To solve this problem, when calling f2fs_balance_fs, check whether
>>>>> the extent cache is sufficient. If not, release the zombie extent
>>>>> tree.
>>>>>
>>>>> Signed-off-by: Xiuhong Wang <xiuhong.wang@...soc.com>
>>>>> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
>>>>> ---
>>>>> Test the problem with the temporary versions:
>>>>> patch did not reproduce the problem, the patch is as follows:
>>>>> @@ -415,7 +415,7 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>>>> f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_FAULT_INJECT);
>>>>>
>>>>> /* balance_fs_bg is able to be pending */
>>>>> - if (need && excess_cached_nats(sbi))
>>>>> + if (need)
>>>>> f2fs_balance_fs_bg(sbi, false);
>>>>>
>>>>> ---
>>>>> fs/f2fs/segment.c | 4 +++-
>>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>> index 1766254279d2..390bec177567 100644
>>>>> --- a/fs/f2fs/segment.c
>>>>> +++ b/fs/f2fs/segment.c
>>>>> @@ -415,7 +415,9 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>>>> f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_FAULT_INJECT);
>>>>>
>>>>> /* balance_fs_bg is able to be pending */
>>>>> - if (need && excess_cached_nats(sbi))
>>>>> + if (need && (excess_cached_nats(sbi) ||
>>>>> + !f2fs_available_free_memory(sbi, READ_EXTENT_CACHE) ||
>>>>> + !f2fs_available_free_memory(sbi, AGE_EXTENT_CACHE)))
>>>>
>>>> Hi,
>>>>
>>>> I doubt if there is no enough memory, we may still run into
>>>> f2fs_shrink_extent_tree() and suffer such long time delay.
>>>>
>>>> So, can we just let __free_extent_tree() break the loop once we have
>>>> released entries w/ target number? something like this:
>>>>
>>>> ---
>>>> fs/f2fs/extent_cache.c | 15 ++++++++++-----
>>>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>>>> index 019c1f7b7fa5..38c71c1c4fb7 100644
>>>> --- a/fs/f2fs/extent_cache.c
>>>> +++ b/fs/f2fs/extent_cache.c
>>>> @@ -379,11 +379,12 @@ static struct extent_tree *__grab_extent_tree(struct inode *inode,
>>>> }
>>>>
>>>> static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
>>>> - struct extent_tree *et)
>>>> + struct extent_tree *et, unsigned int nr_shrink)
>>>> {
>>>> struct rb_node *node, *next;
>>>> struct extent_node *en;
>>>> unsigned int count = atomic_read(&et->node_cnt);
>>>> + unsigned int i = 0;
>>>>
>>>> node = rb_first_cached(&et->root);
>>>> while (node) {
>>>> @@ -391,6 +392,9 @@ static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
>>>> en = rb_entry(node, struct extent_node, rb_node);
>>>> __release_extent_node(sbi, et, en);
>>>> node = next;
>>>> +
>>>> + if (nr_shrink && ++i >= nr_shrink)
>>>> + break;
>>>> }
>>>>
>>>> return count - atomic_read(&et->node_cnt);
>>>> @@ -761,7 +765,7 @@ static void __update_extent_tree_range(struct inode *inode,
>>>> }
>>>>
>>>> if (is_inode_flag_set(inode, FI_NO_EXTENT))
>>>> - __free_extent_tree(sbi, et);
>>>> + __free_extent_tree(sbi, et, 0);
>>>>
>>>> if (et->largest_updated) {
>>>> et->largest_updated = false;
>>>> @@ -942,7 +946,8 @@ static unsigned int __shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink
>>>> list_for_each_entry_safe(et, next, &eti->zombie_list, list) {
>>>> if (atomic_read(&et->node_cnt)) {
>>>> write_lock(&et->lock);
>>>> - node_cnt += __free_extent_tree(sbi, et);
>>>> + node_cnt += __free_extent_tree(sbi, et,
>>>> + nr_shrink - node_cnt - tree_cnt);
>>>> write_unlock(&et->lock);
>>>> }
>>>> f2fs_bug_on(sbi, atomic_read(&et->node_cnt));
>>>> @@ -1095,7 +1100,7 @@ static unsigned int __destroy_extent_node(struct inode *inode,
>>>> return 0;
>>>>
>>>> write_lock(&et->lock);
>>>> - node_cnt = __free_extent_tree(sbi, et);
>>>> + node_cnt = __free_extent_tree(sbi, et, 0);
>>>> write_unlock(&et->lock);
>>>>
>>>> return node_cnt;
>>>> @@ -1117,7 +1122,7 @@ static void __drop_extent_tree(struct inode *inode, enum extent_type type)
>>>> return;
>>>>
>>>> write_lock(&et->lock);
>>>> - __free_extent_tree(sbi, et);
>>>> + __free_extent_tree(sbi, et, 0);
>>>> if (type == EX_READ) {
>>>> set_inode_flag(inode, FI_NO_EXTENT);
>>>> if (et->largest.len) {
>>>> --
>>>> 2.40.1
>>>>
>>>> Thanks,
>>>>
>>>>> f2fs_balance_fs_bg(sbi, false);
>>>>>
>>>>> if (!f2fs_is_checkpoint_ready(sbi))
>>>>
>>>
>>>
>>> Hi chao,
>>>
>>> We have also considered this approach, but the problem still occurs
>>> after retesting.
>>> 1. The problem still occurs in the following call of the unmount data process.
>>> f2fs_put_super -> f2fs_leave_shrinker
>>
>> Yes, I guess we need to fix this path as well, however, your patch didn't
>> cover this path as well, am I missing something?
> Dear Chao,
> This patch version aim to shrink extent cache as early as possible on
> the "all write path"
> by "write action" -> f2fs_balance_fs -> f2fs_balance_fs_bg
Zhiguo, thanks for explaining again.
However, I doubt covering all write paths is not enough, because extent
node can increase when f2fs_precache_extents() was called from paths
including fadvise/fiemap/swapon/ioc_precache_extents, and there may be
no writeback, so we may get no chance to call into f2fs_balance_fs_bg(),
e.g. there is no data update in mountpoint, or mountpoint is readonly.
> As the comment , the "excess_cached_nats" is difficult to achieve in
> this scenario, and
Another concern is, in high-end products w/ more memory, it may has less
chance to hit newly added condition in f2fs_balance_fs()? not sure though.
+ if (need && (excess_cached_nats(sbi) ||
+ !f2fs_available_free_memory(sbi, READ_EXTENT_CACHE) ||
+ !f2fs_available_free_memory(sbi, AGE_EXTENT_CACHE)))
I mean will f2fs_available_free_memory(sbi, {READ,AGE}_EXTENT_CACHE)
return true if available memory is sufficient?
Thanks,
> trigger the issue in path f2fs_write_node_pages->f2fs_balance_fs_bg(is
> called directly here).
> At that time, there were already a lot of extent node cnt.
> Thanks!
>>
>>> 2. Writing back the inode in the normal write-back process will
>>> release the extent cache, and the problem still occurs. The stack is
>>> as follows:
>>
>> Ditto,
>>
>> Thanks,
>>
>>> [H 103098.974356] c2 [<ffffffc008aee8a4>] (rb_erase+0x204/0x334)
>>> [H 103098.974389] c2 [<ffffffc0088f8fd0>] (__release_extent_node+0xc8/0x168)
>>> [H 103098.974425] c2 [<ffffffc0088fad74>]
>>> (f2fs_update_extent_tree_range+0x4a0/0x724)
>>> [H 103098.974459] c2 [<ffffffc0088fa8c0>] (f2fs_update_extent_cache+0x19c/0x1b0)
>>> [H 103098.974495] c2 [<ffffffc0088edc70>] (f2fs_outplace_write_data+0x74/0xf0)
>>> [H 103098.974525] c2 [<ffffffc0088ca834>] (f2fs_do_write_data_page+0x3e4/0x6c8)
>>> [H 103098.974552] c2 [<ffffffc0088cb150>]
>>> (f2fs_write_single_data_page+0x478/0xab0)
>>> [H 103098.974574] c2 [<ffffffc0088d0bd0>] (f2fs_write_cache_pages+0x454/0xaac)
>>> [H 103098.974596] c2 [<ffffffc0088d0698>] (__f2fs_write_data_pages+0x40c/0x4f0)
>>> [H 103098.974617] c2 [<ffffffc0088cc860>] (f2fs_write_data_pages+0x30/0x40)
>>> [H 103098.974645] c2 [<ffffffc0084c0e00>] (do_writepages+0x18c/0x3e8)
>>> [H 103098.974678] c2 [<ffffffc0086503cc>] (__writeback_single_inode+0x48/0x498)
>>> [H 103098.974720] c2 [<ffffffc0086562c8>] (writeback_sb_inodes+0x454/0x9b0)
>>> [H 103098.974754] c2 [<ffffffc008655de8>] (__writeback_inodes_wb+0x198/0x224)
>>> [H 103098.974788] c2 [<ffffffc008656d0c>] (wb_writeback+0x1c0/0x698)
>>> [H 103098.974819] c2 [<ffffffc008655614>] (wb_do_writeback+0x420/0x54c)
>>> [H 103098.974853] c2 [<ffffffc008654f50>] (wb_workfn+0xe4/0x388)
>>
Powered by blists - more mailing lists