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Message-ID: <CACOAw_w3Tn6HL9hZXFgpjpgu9ySvE_0FbTWMMBuZKgRFBYXXLA@mail.gmail.com>
Date: Wed, 4 Sep 2024 07:56:00 -0700
From: Daeho Jeong <daeho43@...il.com>
To: Chao Yu <chao@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, 
	kernel-team@...roid.com, Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: prevent atomic file from being dirtied
 before commit

On Tue, Sep 3, 2024 at 8:35 PM Chao Yu <chao@...nel.org> wrote:
>
> On 2024/9/4 10:52, Daeho Jeong wrote:
> > On Tue, Sep 3, 2024 at 7:26 PM Chao Yu <chao@...nel.org> wrote:
> >>
> >> On 2024/9/4 1:07, Daeho Jeong wrote:
> >>> On Mon, Sep 2, 2024 at 3:08 AM Chao Yu <chao@...nel.org> wrote:
> >>>>
> >>>> On 2024/8/27 4:23, Daeho Jeong wrote:
> >>>>> From: Daeho Jeong <daehojeong@...gle.com>
> >>>>>
> >>>>> 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@...gle.com>
> >>>>> ---
> >>>>>     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@kernel.org
>
> 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);
> >>>>
> >>
>

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