linux-kernel - Re: [f2fs-dev] [PATCH v2] f2fs: fix to read source block before invalidating it

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Message-ID: <20190729055454.GC94090@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Sun, 28 Jul 2019 22:54:54 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: fix to read source block before
 invalidating it

On 07/23, Chao Yu wrote:
> On 2019/7/23 9:27, Jaegeuk Kim wrote:
> > On 07/18, Chao Yu wrote:
> >> On 2019/7/18 12:00, Jaegeuk Kim wrote:
> >>> On 07/18, Chao Yu wrote:
> >>>> On 2019/7/18 11:12, Jaegeuk Kim wrote:
> >>>>> f2fs_allocate_data_block() invalidates old block address and enable new block
> >>>>> address. Then, if we try to read old block by f2fs_submit_page_bio(), it will
> >>>>> give WARN due to reading invalid blocks.
> >>>>>
> >>>>> Let's make the order sanely back.
> >>>>
> >>>> Hmm.. to avoid WARM, we may suffer one more memcpy, I suspect this can reduce
> >>>> online resize or foreground gc ioctl performance...
> >>>
> >>> I worried about performance tho, more concern came to me that there may exist a
> >>> chance that other thread can allocate and write something in old block address.
> >>
> >> Me too, however, previous invalid block address should be reused after a
> >> checkpoint, and checkpoint should have invalidated meta cache already, so there
> >> shouldn't be any race here.
> > 
> > I think SSR can reuse that before checkpoint.
> 
> Yes, I should have considered that when I introduced readahead feature for
> migration of block, we've kept invalidating meta page cache in old block address
> whenever the block address is not valid.
> 
> quoted from ("f2fs: readahead encrypted block during GC")
> 
> "Note that for OPU, truncation, deletion, we need to invalid meta
> page after we invalid old block address, to make sure we won't load
> invalid data from target meta page during encrypted block migration."
> 
> But to avoid potential issue, how about just enable meta page cache during GC?
> that is saying we should truncate all valid meta cache after one section has
> been moved.

We may need to invalidate metapage when writing new data, which looks like
different issue.

> 
> One more concern is whether below case exists during SSR?
> - write 4k to fileA;
> - fsync fileA, 4k data is writebacked to lbaA;
> - write 4k to fileA;
> - kworker flushs 4k to lbaB; dnode contain lbaB didn't be persisted yet;
> - write 4k to fileB;
> - kworker flush 4k to lbaA due to SSR;
> - SPOR  -> dnode with lbaA will be recovered, however lbaA contains fileB's data..

Yes, it seems that's possible. We may need to keep another bitmap to record
all the block allocation?

> 
> Thanks,
> 
> > 
> >>
> >> 	/*
> >> 	 * invalidate intermediate page cache borrowed from meta inode
> >> 	 * which are used for migration of encrypted inode's blocks.
> >> 	 */
> >> 	if (f2fs_sb_has_encrypt(sbi))
> >> 		invalidate_mapping_pages(META_MAPPING(sbi),
> >> 				MAIN_BLKADDR(sbi), MAX_BLKADDR(sbi) - 1);
> >>
> >> Thanks,
> >>
> >>>
> >>>>
> >>>> Can we just relief to use DATA_GENERIC_ENHANCE_READ for this case...?
> >>>
> >>> We need to keep consistency for this api.
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>>>
> >>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>>>
> >>>> Except performance, I'm okay with this change.
> >>>>
> >>>> Reviewed-by: Chao Yu <yuchao0@...wei.com>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>> ---
> >>>>> v2:
> >>>>> I was fixing the comments. :)
> >>>>>
> >>>>>  fs/f2fs/gc.c | 70 +++++++++++++++++++++++++---------------------------
> >>>>>  1 file changed, 34 insertions(+), 36 deletions(-)
> >>>>>
> >>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>>>> index 6691f526fa40..8974672db78f 100644
> >>>>> --- a/fs/f2fs/gc.c
> >>>>> +++ b/fs/f2fs/gc.c
> >>>>> @@ -796,6 +796,29 @@ static int move_data_block(struct inode *inode, block_t bidx,
> >>>>>  	if (lfs_mode)
> >>>>>  		down_write(&fio.sbi->io_order_lock);
> >>>>>  
> >>>>> +	mpage = f2fs_grab_cache_page(META_MAPPING(fio.sbi),
> >>>>> +					fio.old_blkaddr, false);
> >>>>> +	if (!mpage)
> >>>>> +		goto up_out;
> >>>>> +
> >>>>> +	fio.encrypted_page = mpage;
> >>>>> +
> >>>>> +	/* read source block in mpage */
> >>>>> +	if (!PageUptodate(mpage)) {
> >>>>> +		err = f2fs_submit_page_bio(&fio);
> >>>>> +		if (err) {
> >>>>> +			f2fs_put_page(mpage, 1);
> >>>>> +			goto up_out;
> >>>>> +		}
> >>>>> +		lock_page(mpage);
> >>>>> +		if (unlikely(mpage->mapping != META_MAPPING(fio.sbi) ||
> >>>>> +						!PageUptodate(mpage))) {
> >>>>> +			err = -EIO;
> >>>>> +			f2fs_put_page(mpage, 1);
> >>>>> +			goto up_out;
> >>>>> +		}
> >>>>> +	}
> >>>>> +
> >>>>>  	f2fs_allocate_data_block(fio.sbi, NULL, fio.old_blkaddr, &newaddr,
> >>>>>  					&sum, CURSEG_COLD_DATA, NULL, false);
> >>>>>  
> >>>>> @@ -803,44 +826,18 @@ static int move_data_block(struct inode *inode, block_t bidx,
> >>>>>  				newaddr, FGP_LOCK | FGP_CREAT, GFP_NOFS);
> >>>>>  	if (!fio.encrypted_page) {
> >>>>>  		err = -ENOMEM;
> >>>>> -		goto recover_block;
> >>>>> -	}
> >>>>> -
> >>>>> -	mpage = f2fs_pagecache_get_page(META_MAPPING(fio.sbi),
> >>>>> -					fio.old_blkaddr, FGP_LOCK, GFP_NOFS);
> >>>>> -	if (mpage) {
> >>>>> -		bool updated = false;
> >>>>> -
> >>>>> -		if (PageUptodate(mpage)) {
> >>>>> -			memcpy(page_address(fio.encrypted_page),
> >>>>> -					page_address(mpage), PAGE_SIZE);
> >>>>> -			updated = true;
> >>>>> -		}
> >>>>>  		f2fs_put_page(mpage, 1);
> >>>>> -		invalidate_mapping_pages(META_MAPPING(fio.sbi),
> >>>>> -					fio.old_blkaddr, fio.old_blkaddr);
> >>>>> -		if (updated)
> >>>>> -			goto write_page;
> >>>>> -	}
> >>>>> -
> >>>>> -	err = f2fs_submit_page_bio(&fio);
> >>>>> -	if (err)
> >>>>> -		goto put_page_out;
> >>>>> -
> >>>>> -	/* write page */
> >>>>> -	lock_page(fio.encrypted_page);
> >>>>> -
> >>>>> -	if (unlikely(fio.encrypted_page->mapping != META_MAPPING(fio.sbi))) {
> >>>>> -		err = -EIO;
> >>>>> -		goto put_page_out;
> >>>>> -	}
> >>>>> -	if (unlikely(!PageUptodate(fio.encrypted_page))) {
> >>>>> -		err = -EIO;
> >>>>> -		goto put_page_out;
> >>>>> +		goto recover_block;
> >>>>>  	}
> >>>>>  
> >>>>> -write_page:
> >>>>> +	/* write target block */
> >>>>>  	f2fs_wait_on_page_writeback(fio.encrypted_page, DATA, true, true);
> >>>>> +	memcpy(page_address(fio.encrypted_page),
> >>>>> +				page_address(mpage), PAGE_SIZE);
> >>>>> +	f2fs_put_page(mpage, 1);
> >>>>> +	invalidate_mapping_pages(META_MAPPING(fio.sbi),
> >>>>> +				fio.old_blkaddr, fio.old_blkaddr);
> >>>>> +
> >>>>>  	set_page_dirty(fio.encrypted_page);
> >>>>>  	if (clear_page_dirty_for_io(fio.encrypted_page))
> >>>>>  		dec_page_count(fio.sbi, F2FS_DIRTY_META);
> >>>>> @@ -871,11 +868,12 @@ static int move_data_block(struct inode *inode, block_t bidx,
> >>>>>  put_page_out:
> >>>>>  	f2fs_put_page(fio.encrypted_page, 1);
> >>>>>  recover_block:
> >>>>> -	if (lfs_mode)
> >>>>> -		up_write(&fio.sbi->io_order_lock);
> >>>>>  	if (err)
> >>>>>  		f2fs_do_replace_block(fio.sbi, &sum, newaddr, fio.old_blkaddr,
> >>>>>  								true, true);
> >>>>> +up_out:
> >>>>> +	if (lfs_mode)
> >>>>> +		up_write(&fio.sbi->io_order_lock);
> >>>>>  put_out:
> >>>>>  	f2fs_put_dnode(&dn);
> >>>>>  out:
> >>>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> Linux-f2fs-devel mailing list
> >>>> Linux-f2fs-devel@...ts.sourceforge.net
> >>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >>> .
> >>>
> > .
> >