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

[Jaegeuk Kim]

On 04/13, Chao Yu wrote:
> 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?

I suggest to run sqlite transaction/check operations in android devices in parallel.

> 
> 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
> > .
> >