linux-kernel - Re: [PATCH v2 3/4] f2fs: atomic: fix to truncate pagecache before on-disk metadata truncation

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Message-ID: <ZqqeKuEIExOwMyuK@google.com>
Date: Wed, 31 Jul 2024 20:27:22 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] f2fs: atomic: fix to truncate pagecache before
 on-disk metadata truncation

On 07/31, Chao Yu wrote:
> On 2024/7/31 0:26, Jaegeuk Kim wrote:
> > On 07/30, Chao Yu wrote:
> > > On 2024/7/30 0:26, Jaegeuk Kim wrote:
> > > > On 07/26, Chao Yu wrote:
> > > > > We should always truncate pagecache while truncating on-disk data.
> > > > > 
> > > > > Fixes: a46bebd502fe ("f2fs: synchronize atomic write aborts")
> > > > > Signed-off-by: Chao Yu <chao@...nel.org>
> > > > > ---
> > > > > v2:
> > > > > - fix to use cow_inode instead of inode
> > > > >    fs/f2fs/file.c | 1 +
> > > > >    1 file changed, 1 insertion(+)
> > > > > 
> > > > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > > > index 6c62f76474d1..54886ddcb8ab 100644
> > > > > --- a/fs/f2fs/file.c
> > > > > +++ b/fs/f2fs/file.c
> > > > > @@ -2202,6 +2202,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
> > > > >    		F2FS_I(fi->cow_inode)->atomic_inode = inode;
> > > > >    	} else {
> > > > >    		/* Reuse the already created COW inode */
> > > > > +		truncate_setsize(fi->cow_inode, 0);
> > > > 
> > > > What if the below truncation failed?
> > > 
> > > What about just dropping page cache and do not set isize to 0?
> > 
> > Can we also check if there's any dirty page before truncating it?
> 
> Sure, so how about this?
> 
> 		/* Reuse the already created COW inode */
> 		if (get_dirty_pages(fi->cow_inode)) {

Was supposed to be a bug here?

> 			ret = filemap_write_and_wait(fi->cow_inode->i_mapping);
> 			if (ret) {
> 				f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
> 				goto out;
> 			}
> 		}
> 
> 		truncate_inode_pages(fi->cow_inode->i_mapping, 0);

invalidate_mapping_pages() would be much safer?

> 
> 		ret = f2fs_do_truncate_blocks(fi->cow_inode, 0, true);
> 		if (ret) {
> 			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
> 			goto out;
> 		}
> 
> 		i_size_write(fi->cow_inode, 0);
> 
> Thanks,
> 
> > 
> > > 
> > > Thanks,
> > > 
> > > > 
> > > > >    		ret = f2fs_do_truncate_blocks(fi->cow_inode, 0, true);
> > > > >    		if (ret) {
> > > > >    			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
> > > > > -- 
> > > > > 2.40.1