Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files

From: Chao Yu
Date: Mon Sep 09 2019 - 21:04:57 EST

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On 2019/9/9 22:34, Jaegeuk Kim wrote:
> On 09/09, Chao Yu wrote:
>> On 2019/9/9 16:38, Jaegeuk Kim wrote:
>>> On 09/09, Chao Yu wrote:
>>>> On 2019/9/9 16:21, Jaegeuk Kim wrote:
>>>>> On 09/09, Chao Yu wrote:
>>>>>> On 2019/9/9 16:01, Jaegeuk Kim wrote:
>>>>>>> On 09/09, Chao Yu wrote:
>>>>>>>> On 2019/9/9 15:30, Jaegeuk Kim wrote:
>>>>>>>>> On 09/09, Chao Yu wrote:
>>>>>>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote:
>>>>>>>>>>> If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
>>>>>>>>>>> get commited pages but atomic_file being still set like:
>>>>>>>>>>>
>>>>>>>>>>> - inmem: 0, atomic IO: 4 (Max. 10), volatile IO: 0 (Max. 0)
>>>>>>>>>>>
>>>>>>>>>>> If GC selects this block, we can get an infinite loop like this:
>>>>>>>>>>>
>>>>>>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
>>>>>>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
>>>>>>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
>>>>>>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
>>>>>>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
>>>>>>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
>>>>>>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
>>>>>>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
>>>>>>>>>>>
>>>>>>>>>>> In that moment, we can observe:
>>>>>>>>>>>
>>>>>>>>>>> [Before]
>>>>>>>>>>> Try to move 5084219 blocks (BG: 384508)
>>>>>>>>>>> - data blocks : 4962373 (274483)
>>>>>>>>>>> - node blocks : 121846 (110025)
>>>>>>>>>>> Skipped : atomic write 4534686 (10)
>>>>>>>>>>>
>>>>>>>>>>> [After]
>>>>>>>>>>> Try to move 5088973 blocks (BG: 384508)
>>>>>>>>>>> - data blocks : 4967127 (274483)
>>>>>>>>>>> - node blocks : 121846 (110025)
>>>>>>>>>>> Skipped : atomic write 4539440 (10)
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
>>>>>>>>>>> ---
>>>>>>>>>>> fs/f2fs/file.c | 10 +++++-----
>>>>>>>>>>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>>>>>>>>> index 7ae2f3bd8c2f..68b6da734e5f 100644
>>>>>>>>>>> --- a/fs/f2fs/file.c
>>>>>>>>>>> +++ b/fs/f2fs/file.c
>>>>>>>>>>> @@ -1997,11 +1997,11 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>>>>>>>>>> goto err_out;
>>>>>>>>>>>
>>>>>>>>>>> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
>>>>>>>>>>> - if (!ret) {
>>>>>>>>>>> - clear_inode_flag(inode, FI_ATOMIC_FILE);
>>>>>>>>>>> - F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
>>>>>>>>>>> - stat_dec_atomic_write(inode);
>>>>>>>>>>> - }
>>>>>>>>>>> +
>>>>>>>>>>> + /* doesn't need to check error */
>>>>>>>>>>> + clear_inode_flag(inode, FI_ATOMIC_FILE);
>>>>>>>>>>> + F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
>>>>>>>>>>> + stat_dec_atomic_write(inode);
>>>>>>>>>>
>>>>>>>>>> If there are still valid atomic write pages linked in .inmem_pages, it may cause
>>>>>>>>>> memory leak when we just clear FI_ATOMIC_FILE flag.
>>>>>>>>>
>>>>>>>>> f2fs_commit_inmem_pages() should have flushed them.
>>>>>>>>
>>>>>>>> Oh, we failed to flush its nodes.
>>>>>>>>
>>>>>>>> However we won't clear such info if we failed to flush inmen pages, it looks
>>>>>>>> inconsistent.
>>>>>>>>
>>>>>>>> Any interface needed to drop inmem pages or clear ATOMIC_FILE flag in that two
>>>>>>>> error path? I'm not very clear how sqlite handle such error.
>>>>>>>
>>>>>>> f2fs_drop_inmem_pages() did that, but not in this case.
>>>>>>
>>>>>> What I mean is, for any error returned from atomic_commit() interface, should
>>>>>> userspace application handle it with consistent way, like trigger
>>>>>> f2fs_drop_inmem_pages(), so we don't need to handle it inside atomic_commit().
>>>>>
>>>>> f2fs_ioc_abort_volatile_write() will be triggered.
>>>>
>>>> If userspace can do this, we can get rid of this patch, or am I missing sth?
>>>
>>> We don't know when that will come. And, other threads are waiting for GC here.
>>
>> Yes, however, even atomic_write won't be called sometimes... that's why we add
>> handling logic in f2fs_gc().
>
> We need to clean this up like:
>
> If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
> get commited pages but atomic_file being still set like:
>
> - inmem: 0, atomic IO: 4 (Max. 10), volatile IO: 0 (Max. 0)
>
> If GC selects this block, we can get an infinite loop like this:
>
> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
>
> In that moment, we can observe:
>
> [Before]
> Try to move 5084219 blocks (BG: 384508)
> - data blocks : 4962373 (274483)
> - node blocks : 121846 (110025)
> Skipped : atomic write 4534686 (10)
>
> [After]
> Try to move 5088973 blocks (BG: 384508)
> - data blocks : 4967127 (274483)
> - node blocks : 121846 (110025)
> Skipped : atomic write 4539440 (10)
>
> So, refactor atomic_write flow like this:
> 1. start_atomic_write
> - add inmem_list and set atomic_file
>
> 2. write()
> - register it in inmem_pages
>
> 3. commit_atomic_write
> - if no error, f2fs_drop_inmem_pages()
> - f2fs_commit_inmme_pages() failed
> : __revoked_inmem_pages() was done
> - f2fs_do_sync_file failed
> : abort_atomic_write later
>
> 4. abort_atomic_write
> - f2fs_drop_inmem_pages
>
> 5. f2fs_drop_inmem_pages
> - clear atomic_file
> - remove inmem_list

Looks good.

>
> Based on this change, when GC fails to move block in atomic_file,
> f2fs_drop_inmem_pages_all() can call f2fs_drop_inmem_pages().
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
> fs/f2fs/file.c | 17 +++++++++++------
> fs/f2fs/segment.c | 24 +++++-------------------
> 2 files changed, 16 insertions(+), 25 deletions(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 10927a0b8df3..1f499ac13d9a 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1830,6 +1830,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> {
> struct inode *inode = file_inode(filp);
> int ret;
> + struct f2fs_inode_info *fi = F2FS_I(inode);
>
> if (!inode_owner_or_capable(inode))
> return -EACCES;
> @@ -1871,10 +1872,17 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> goto out;
> }
>
> - set_inode_flag(inode, FI_ATOMIC_FILE);
> clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>
> + spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> + if (list_empty(&fi->inmem_ilist))
> + list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
> + spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> +
> + /* add inode in inmem_list first and set atomic_file */
> + set_inode_flag(inode, FI_ATOMIC_FILE);

Should call up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]) here? Then in f2fs_gc(),
we can check FI_ATOMIC_FILE atomically under i_gc_rwsem.

Thanks,

> +
> f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> F2FS_I(inode)->inmem_task = current;
> stat_inc_atomic_write(inode);
> @@ -1912,11 +1920,8 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> goto err_out;
>
> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
> - if (!ret) {
> - clear_inode_flag(inode, FI_ATOMIC_FILE);
> - F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> - stat_dec_atomic_write(inode);
> - }
> + if (!ret)
> + f2fs_drop_inmem_pages(inode);
> } else {
> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
> }
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 18584d4c078a..a36bc8bf04c3 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -186,7 +186,6 @@ bool f2fs_need_SSR(struct f2fs_sb_info *sbi)
> void f2fs_register_inmem_page(struct inode *inode, struct page *page)
> {
> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> - struct f2fs_inode_info *fi = F2FS_I(inode);
> struct inmem_pages *new;
>
> f2fs_trace_pid(page);
> @@ -200,15 +199,9 @@ void f2fs_register_inmem_page(struct inode *inode, struct page *page)
> INIT_LIST_HEAD(&new->list);
>
> /* increase reference count with clean state */
> - mutex_lock(&fi->inmem_lock);
> get_page(page);
> list_add_tail(&new->list, &fi->inmem_pages);
> - spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> - if (list_empty(&fi->inmem_ilist))
> - list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
> - spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> inc_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
> - mutex_unlock(&fi->inmem_lock);
>
> trace_f2fs_register_inmem_page(page, INMEM);
> }
> @@ -330,19 +323,17 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> mutex_lock(&fi->inmem_lock);
> __revoke_inmem_pages(inode, &fi->inmem_pages,
> true, false, true);
> -
> - if (list_empty(&fi->inmem_pages)) {
> - spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> - if (!list_empty(&fi->inmem_ilist))
> - list_del_init(&fi->inmem_ilist);
> - spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> - }
> mutex_unlock(&fi->inmem_lock);
> }
>
> clear_inode_flag(inode, FI_ATOMIC_FILE);
> fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> stat_dec_atomic_write(inode);
> +
> + spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> + if (!list_empty(&fi->inmem_ilist))
> + list_del_init(&fi->inmem_ilist);
> + spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> }
>
> void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
> @@ -471,11 +462,6 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>
> mutex_lock(&fi->inmem_lock);
> err = __f2fs_commit_inmem_pages(inode);
> -
> - spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
> - if (!list_empty(&fi->inmem_ilist))
> - list_del_init(&fi->inmem_ilist);
> - spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> mutex_unlock(&fi->inmem_lock);
>
> clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>

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