Re: [PATCH v3] f2fs: fix to keep isolation of atomic write

[Chao Yu]

On 2021/4/13 11:27, Jaegeuk Kim wrote:
> On 04/12, Chao Yu wrote:
> > As Yi Chen reported, there is a potential race case described as below:
> >
> > Thread A			Thread B
> > - f2fs_ioc_start_atomic_write
> > 				- mkwrite
> > 				 - set_page_dirty
> > 				  - f2fs_set_page_private(page, 0)
> >   - set_inode_flag(FI_ATOMIC_FILE)
> > 				- mkwrite same page
> > 				 - set_page_dirty
> > 				  - f2fs_register_inmem_page
> > 				   - f2fs_set_page_private(ATOMIC_WRITTEN_PAGE)
> > 				     failed due to PagePrivate flag has been set
> > 				   - list_add_tail
> > 				- truncate_inode_pages
> > 				 - f2fs_invalidate_page
> > 				  - clear page private but w/o remove it from
> > 				    inmem_list
> > 				 - set page->mapping to NULL
> > - f2fs_ioc_commit_atomic_write
> >   - __f2fs_commit_inmem_pages
> >     - __revoke_inmem_pages
> >      - f2fs_put_page panic as page->mapping is NULL
> >
> > The root cause is we missed to keep isolation of atomic write in the case
> > of start_atomic_write vs mkwrite, let start_atomic_write helds i_mmap_sem
> > lock to avoid this issue.
>
> My only concern is performance regression. Could you please verify the numbers?

Do you have specific test script?

IIRC, the scenario you mean is multi-threads write/mmap the same db, right?

Thanks,

> > Reported-by: Yi Chen <chenyi77@xxxxxxxxxx>
> > Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> > ---
> > v3:
> > - rebase to last dev branch
> > - update commit message because this patch fixes a different racing issue
> > of atomic write
> >   fs/f2fs/file.c    | 3 +++
> >   fs/f2fs/segment.c | 6 ++++++
> >   2 files changed, 9 insertions(+)
> >
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index d697c8900fa7..6284b2f4a60b 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -2054,6 +2054,7 @@ 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
> > @@ -2064,6 +2065,7 @@ 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;
> >   	}
> > @@ -2077,6 +2079,7 @@ 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 0cb1ca88d4aa..78c8342f52fd 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -325,6 +325,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> >   	struct f2fs_inode_info *fi = F2FS_I(inode);
> >   
> >   	do {
> > +		down_write(&F2FS_I(inode)->i_mmap_sem);
> >   		mutex_lock(&fi->inmem_lock);
> >   		if (list_empty(&fi->inmem_pages)) {
> >   			fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> > @@ -339,11 +340,13 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> >   			spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >   
> >   			mutex_unlock(&fi->inmem_lock);
> > +			up_write(&F2FS_I(inode)->i_mmap_sem);
> >   			break;
> >   		}
> >   		__revoke_inmem_pages(inode, &fi->inmem_pages,
> >   						true, false, true);
> >   		mutex_unlock(&fi->inmem_lock);
> > +		up_write(&F2FS_I(inode)->i_mmap_sem);
> >   	} while (1);
> >   }
> >   
> > @@ -468,6 +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);
> > @@ -479,6 +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
> .