Re: [f2fs-dev] [PATCH] f2fs: prevent atomic file from being dirtied before commit

From: Daeho Jeong
Date: Wed Sep 04 2024 - 10:56:46 EST

On Tue, Sep 3, 2024 at 8:35 PM Chao Yu <chao@xxxxxxxxxx> wrote:
>
> On 2024/9/4 10:52, Daeho Jeong wrote:
> > On Tue, Sep 3, 2024 at 7:26 PM Chao Yu <chao@xxxxxxxxxx> wrote:
> >>
> >> On 2024/9/4 1:07, Daeho Jeong wrote:
> >>> On Mon, Sep 2, 2024 at 3:08 AM Chao Yu <chao@xxxxxxxxxx> wrote:
> >>>>
> >>>> On 2024/8/27 4:23, Daeho Jeong wrote:
> >>>>> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >>>>>
> >>>>> Keep atomic file clean while updating and make it dirtied during commit
> >>>>> in order to avoid unnecessary and excessive inode updates in the previous
> >>>>> fix.
> >>>>>
> >>>>> Fixes: 4bf78322346f ("f2fs: mark inode dirty for FI_ATOMIC_COMMITTED flag")
> >>>>> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >>>>> ---
> >>>>> fs/f2fs/f2fs.h | 3 +--
> >>>>> fs/f2fs/inode.c | 10 ++++++----
> >>>>> fs/f2fs/segment.c | 10 ++++++++--
> >>>>> 3 files changed, 15 insertions(+), 8 deletions(-)
> >>>>>
> >>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>>>> index 465b2fd50c70..5a7f6fa8b585 100644
> >>>>> --- a/fs/f2fs/f2fs.h
> >>>>> +++ b/fs/f2fs/f2fs.h
> >>>>> @@ -801,7 +801,7 @@ enum {
> >>>>> FI_COMPRESS_RELEASED, /* compressed blocks were released */
> >>>>> FI_ALIGNED_WRITE, /* enable aligned write */
> >>>>> FI_COW_FILE, /* indicate COW file */
> >>>>> - FI_ATOMIC_COMMITTED, /* indicate atomic commit completed except disk sync */
> >>>>> + FI_ATOMIC_DIRTIED, /* indicate atomic file is dirtied */
> >>>>> FI_ATOMIC_REPLACE, /* indicate atomic replace */
> >>>>> FI_OPENED_FILE, /* indicate file has been opened */
> >>>>> FI_MAX, /* max flag, never be used */
> >>>>> @@ -3042,7 +3042,6 @@ static inline void __mark_inode_dirty_flag(struct inode *inode,
> >>>>> case FI_INLINE_DOTS:
> >>>>> case FI_PIN_FILE:
> >>>>> case FI_COMPRESS_RELEASED:
> >>>>> - case FI_ATOMIC_COMMITTED:
> >>>>> f2fs_mark_inode_dirty_sync(inode, true);
> >>>>> }
> >>>>> }
> >>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> >>>>> index 1eb250c6b392..5dd3e55d2be2 100644
> >>>>> --- a/fs/f2fs/inode.c
> >>>>> +++ b/fs/f2fs/inode.c
> >>>>> @@ -35,6 +35,11 @@ void f2fs_mark_inode_dirty_sync(struct inode *inode, bool sync)
> >>>>> if (f2fs_inode_dirtied(inode, sync))
> >>>>
> >>>> It will return directly here if inode was dirtied, so it may missed to set
> >>>> FI_ATOMIC_DIRTIED flag?
> >>>
> >>> Is it possible for it to be already dirty, since we already made it
> >>> clean with f2fs_write_inode() when we started the atomic write?
> >>
> >> Some ioctl interfaces may race w/ atomic write? e.g. set_pin_file won't
> >> check atomic_file status, and may dirty inode after we started atomic
> >> write, so we'd better detect such race condition and break ioctl to
> >> avoid ruin atomic write? and maybe we can add f2fs_bug_on() in
> >> f2fs_mark_inode_dirty_sync() to detect any other missing cases?
> >>
> >
> > How about exchanging the positions of f2fs_write_inode() and
> > set_inode_flag() in f2fs_ioc_start_atomic_write()?
> >
> > ...
> > f2fs_write_inode(inode, NULL);
> >
> > stat_inc_atomic_inode(inode);
> >
> > set_inode_flag(inode, FI_ATOMIC_FILE);
> > ...
>
> Oh, I'm not sure I've got your point, after exchanging we still may suffer
> below race condition, right?
>
> - f2fs_ioc_start_atomic_write
> - set_inode_flag(inode, FI_ATOMIC_FILE)
> - f2fs_write_inode(inode, NULL)
> - f2fs_ioc_set_pin_file
> - set_inode_flag(inode, FI_PIN_FILE)
> - __mark_inode_dirty_flag()
=> This attempt will
be blocked by the below condition.

+ if (f2fs_is_atomic_file(inode)) {
+ set_inode_flag(inode, FI_ATOMIC_DIRTIED);
+ return;
+ }

Plz, refer to the above comment.

> - f2fs_ioc_commit_atomic_write
>
> So that I proposed a fix for this:
> https://lore.kernel.org/linux-f2fs-devel/20240904032047.1264706-1-chao@xxxxxxxxxx
>
> Thanks,
>
> >
> >> Thanks,
> >>
> >>>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>> return;
> >>>>>
> >>>>> + if (f2fs_is_atomic_file(inode)) {
> >>>>> + set_inode_flag(inode, FI_ATOMIC_DIRTIED);
> >>>>> + return;
> >>>>> + }
> >>>>> +
> >>>>> mark_inode_dirty_sync(inode);
> >>>>> }
> >>>>>
> >>>>> @@ -653,10 +658,7 @@ void f2fs_update_inode(struct inode *inode, struct page *node_page)
> >>>>> ri->i_gid = cpu_to_le32(i_gid_read(inode));
> >>>>> ri->i_links = cpu_to_le32(inode->i_nlink);
> >>>>> ri->i_blocks = cpu_to_le64(SECTOR_TO_BLOCK(inode->i_blocks) + 1);
> >>>>> -
> >>>>> - if (!f2fs_is_atomic_file(inode) ||
> >>>>> - is_inode_flag_set(inode, FI_ATOMIC_COMMITTED))
> >>>>> - ri->i_size = cpu_to_le64(i_size_read(inode));
> >>>>> + ri->i_size = cpu_to_le64(i_size_read(inode));
> >>>>>
> >>>>> if (et) {
> >>>>> read_lock(&et->lock);
> >>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>>> index 78c3198a6308..2b5391b229a8 100644
> >>>>> --- a/fs/f2fs/segment.c
> >>>>> +++ b/fs/f2fs/segment.c
> >>>>> @@ -196,9 +196,12 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean)
> >>>>> truncate_inode_pages_final(inode->i_mapping);
> >>>>>
> >>>>> release_atomic_write_cnt(inode);
> >>>>> - clear_inode_flag(inode, FI_ATOMIC_COMMITTED);
> >>>>> clear_inode_flag(inode, FI_ATOMIC_REPLACE);
> >>>>> clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>> + if (is_inode_flag_set(inode, FI_ATOMIC_DIRTIED)) {
> >>>>> + clear_inode_flag(inode, FI_ATOMIC_DIRTIED);
> >>>>> + f2fs_mark_inode_dirty_sync(inode, true);
> >>>>> + }
> >>>>> stat_dec_atomic_inode(inode);
> >>>>>
> >>>>> F2FS_I(inode)->atomic_write_task = NULL;
> >>>>> @@ -365,7 +368,10 @@ static int __f2fs_commit_atomic_write(struct inode *inode)
> >>>>> sbi->revoked_atomic_block += fi->atomic_write_cnt;
> >>>>> } else {
> >>>>> sbi->committed_atomic_block += fi->atomic_write_cnt;
> >>>>> - set_inode_flag(inode, FI_ATOMIC_COMMITTED);
> >>>>> + if (is_inode_flag_set(inode, FI_ATOMIC_DIRTIED)) {
> >>>>> + clear_inode_flag(inode, FI_ATOMIC_DIRTIED);
> >>>>> + f2fs_mark_inode_dirty_sync(inode, true);
> >>>>> + }
> >>>>> }
> >>>>>
> >>>>> __complete_revoke_list(inode, &revoke_list, ret ? true : false);
> >>>>
> >>
>