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Date:   Wed, 6 Jan 2021 14:57:15 -0800
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: fix to keep isolation of atomic write
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References: <20201230075557.108818-1-yuchao0@huawei.com>
 <X/Y5pJr4Aaf0bBqj@google.com>
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On 01/06, Jaegeuk Kim wrote:
> Hi Chao,
> 
> With a quick test, this patch causes down_write failure resulting in blocking
> process. I didn't dig in the bug so, please check the code again. :P

nvm. I can see it works now.

> 
> On 12/30, Chao Yu wrote:
> > ThreadA					ThreadB
> > - f2fs_ioc_start_atomic_write
> > - write
> > - f2fs_ioc_commit_atomic_write
> >  - f2fs_commit_inmem_pages
> >  - f2fs_drop_inmem_pages
> >  - f2fs_drop_inmem_pages
> >   - __revoke_inmem_pages
> > 					- f2fs_vm_page_mkwrite
> > 					 - set_page_dirty
> > 					  - tag ATOMIC_WRITTEN_PAGE and add page
> > 					    to inmem_pages list
> >   - clear_inode_flag(FI_ATOMIC_FILE)
> > 					- f2fs_vm_page_mkwrite
> > 					  - set_page_dirty
> > 					   - f2fs_update_dirty_page
> > 					    - f2fs_trace_pid
> > 					     - tag inmem page private to pid
> > 					- truncate
> > 					 - f2fs_invalidate_page
> > 					 - set page->mapping to NULL
> > 					  then it will cause panic once we
> > 					  access page->mapping
> > 
> > The root cause is we missed to keep isolation of atomic write in the case
> > of commit_atomic_write vs mkwrite, let commit_atomic_write helds i_mmap_sem
> > lock to avoid this issue.
> > 
> > Signed-off-by: Chao Yu <yuchao0@huawei.com>
> > ---
> > v2:
> > - use i_mmap_sem to avoid mkwrite racing with below flows:
> >  * f2fs_ioc_start_atomic_write
> >  * f2fs_drop_inmem_pages
> >  * f2fs_commit_inmem_pages
> > 
> >  fs/f2fs/file.c    | 3 +++
> >  fs/f2fs/segment.c | 7 +++++++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 4e6d4b9120a8..a48ec650d691 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -2050,6 +2050,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  		goto out;
> >  
> >  	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +	down_write(&F2FS_I(inode)->i_mmap_sem);
> >  
> >  	/*
> >  	 * Should wait end_io to count F2FS_WB_CP_DATA correctly by
> > @@ -2060,6 +2061,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  			  inode->i_ino, get_dirty_pages(inode));
> >  	ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
> >  	if (ret) {
> > +		up_write(&F2FS_I(inode)->i_mmap_sem);
> >  		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  		goto out;
> >  	}
> > @@ -2073,6 +2075,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >  	/* add inode in inmem_list first and set atomic_file */
> >  	set_inode_flag(inode, FI_ATOMIC_FILE);
> >  	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> > +	up_write(&F2FS_I(inode)->i_mmap_sem);
> >  	up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >  
> >  	f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index d8570b0359f5..dab870d9faf6 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -327,6 +327,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> >  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >  	struct f2fs_inode_info *fi = F2FS_I(inode);
> >  
> > +	down_write(&F2FS_I(inode)->i_mmap_sem);
> > +
> >  	while (!list_empty(&fi->inmem_pages)) {
> >  		mutex_lock(&fi->inmem_lock);
> >  		__revoke_inmem_pages(inode, &fi->inmem_pages,
> > @@ -344,6 +346,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> >  		sbi->atomic_files--;
> >  	}
> >  	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > +
> > +	up_write(&F2FS_I(inode)->i_mmap_sem);
> >  }
> >  
> >  void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
> > @@ -467,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >  	f2fs_balance_fs(sbi, true);
> >  
> >  	down_write(&fi->i_gc_rwsem[WRITE]);
> > +	down_write(&F2FS_I(inode)->i_mmap_sem);
> >  
> >  	f2fs_lock_op(sbi);
> >  	set_inode_flag(inode, FI_ATOMIC_COMMIT);
> > @@ -478,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >  	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
> >  
> >  	f2fs_unlock_op(sbi);
> > +
> > +	up_write(&F2FS_I(inode)->i_mmap_sem);
> >  	up_write(&fi->i_gc_rwsem[WRITE]);
> >  
> >  	return err;
> > -- 
> > 2.29.2
> 
> 
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