Re: [PATCH V4] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Jaegeuk Kim]

On 05/12, Chao Yu wrote:
> On 2020/5/12 6:11, Jaegeuk Kim wrote:
> > On 05/11, Chao Yu wrote:
> >> On 2020/5/10 3:03, Jaegeuk Kim wrote:
> >>> On 05/09, Chao Yu wrote:
> >>>> On 2020/5/9 0:10, Jaegeuk Kim wrote:
> >>>>> Hi Sayali,
> >>>>>
> >>>>> In order to address the perf regression, how about this?
> >>>>>
> >>>>> >From 48418af635884803ffb35972df7958a2e6649322 Mon Sep 17 00:00:00 2001
> >>>>> From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>>>> Date: Fri, 8 May 2020 09:08:37 -0700
> >>>>> Subject: [PATCH] f2fs: avoid double lock for cp_rwsem during checkpoint
> >>>>>
> >>>>> There could be a scenario where f2fs_sync_node_pages gets
> >>>>> called during checkpoint, which in turn tries to flush
> >>>>> inline data and calls iput(). This results in deadlock as
> >>>>> iput() tries to hold cp_rwsem, which is already held at the
> >>>>> beginning by checkpoint->block_operations().
> >>>>>
> >>>>> Call stack :
> >>>>>
> >>>>> Thread A		Thread B
> >>>>> f2fs_write_checkpoint()
> >>>>> - block_operations(sbi)
> >>>>>  - f2fs_lock_all(sbi);
> >>>>>   - down_write(&sbi->cp_rwsem);
> >>>>>
> >>>>>                         - open()
> >>>>>                          - igrab()
> >>>>>                         - write() write inline data
> >>>>>                         - unlink()
> >>>>> - f2fs_sync_node_pages()
> >>>>>  - if (is_inline_node(page))
> >>>>>   - flush_inline_data()
> >>>>>    - ilookup()
> >>>>>      page = f2fs_pagecache_get_page()
> >>>>>      if (!page)
> >>>>>       goto iput_out;
> >>>>>      iput_out:
> >>>>> 			-close()
> >>>>> 			-iput()
> >>>>>        iput(inode);
> >>>>>        - f2fs_evict_inode()
> >>>>>         - f2fs_truncate_blocks()
> >>>>>          - f2fs_lock_op()
> >>>>>            - down_read(&sbi->cp_rwsem);
> >>>>>
> >>>>> Fixes: 2049d4fcb057 ("f2fs: avoid multiple node page writes due to inline_data")
> >>>>> Signed-off-by: Sayali Lokhande <sayalil@xxxxxxxxxxxxxx>
> >>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>>>> ---
> >>>>>  fs/f2fs/node.c | 4 ++--
> >>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> >>>>> index 1db8cabf727ef..626d7daca09de 100644
> >>>>> --- a/fs/f2fs/node.c
> >>>>> +++ b/fs/f2fs/node.c
> >>>>> @@ -1870,8 +1870,8 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
> >>>>>  				goto continue_unlock;
> >>>>>  			}
> >>>>>  
> >>>>> -			/* flush inline_data */
> >>>>> -			if (is_inline_node(page)) {
> >>>>> +			/* flush inline_data, if it's not sync path. */
> >>>>> +			if (do_balance && is_inline_node(page)) {
> >>>>
> >>>> IIRC, this flow was designed to avoid running out of free space issue
> >>>> during checkpoint:
> >>>>
> >>>> 2049d4fcb057 ("f2fs: avoid multiple node page writes due to inline_data")
> >>>>
> >>>> The sceanrio is:
> >>>> 1. create fully node blocks
> >>>> 2. flush node blocks
> >>>> 3. write inline_data for all the node blocks again
> >>>> 4. flush node blocks redundantly
> >>>>
> >>>> I guess this may cause failing one case of fstest.
> >>>
> >>> Yeah, actually I was hitting 204 failure, and thus, revised like this.
> >>> Now, I don't see any regression in fstest.
> >>>
> >>> >From 8f1882acfb0a5fc43e5a2bbd576a8f3c681a7d2c Mon Sep 17 00:00:00 2001
> >>> From: Sayali Lokhande <sayalil@xxxxxxxxxxxxxx>
> >>> Date: Thu, 30 Apr 2020 16:28:29 +0530
> >>> Subject: [PATCH] f2fs: Avoid double lock for cp_rwsem during checkpoint
> >>>
> >>> There could be a scenario where f2fs_sync_node_pages gets
> >>> called during checkpoint, which in turn tries to flush
> >>> inline data and calls iput(). This results in deadlock as
> >>> iput() tries to hold cp_rwsem, which is already held at the
> >>> beginning by checkpoint->block_operations().
> >>>
> >>> Call stack :
> >>>
> >>> Thread A		Thread B
> >>> f2fs_write_checkpoint()
> >>> - block_operations(sbi)
> >>>  - f2fs_lock_all(sbi);
> >>>   - down_write(&sbi->cp_rwsem);
> >>>
> >>>                         - open()
> >>>                          - igrab()
> >>>                         - write() write inline data
> >>>                         - unlink()
> >>> - f2fs_sync_node_pages()
> >>>  - if (is_inline_node(page))
> >>>   - flush_inline_data()
> >>>    - ilookup()
> >>>      page = f2fs_pagecache_get_page()
> >>>      if (!page)
> >>>       goto iput_out;
> >>>      iput_out:
> >>> 			-close()
> >>> 			-iput()
> >>>        iput(inode);
> >>>        - f2fs_evict_inode()
> >>>         - f2fs_truncate_blocks()
> >>>          - f2fs_lock_op()
> >>>            - down_read(&sbi->cp_rwsem);
> >>>
> >>> Fixes: 2049d4fcb057 ("f2fs: avoid multiple node page writes due to inline_data")
> >>> Signed-off-by: Sayali Lokhande <sayalil@xxxxxxxxxxxxxx>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>> ---
> >>>  fs/f2fs/checkpoint.c |  9 ++++++++-
> >>>  fs/f2fs/f2fs.h       |  4 ++--
> >>>  fs/f2fs/node.c       | 10 +++++-----
> >>>  3 files changed, 15 insertions(+), 8 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index d49f7a01d8a26..928aea4ff663d 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -1168,6 +1168,12 @@ static int block_operations(struct f2fs_sb_info *sbi)
> >>>  	};
> >>>  	int err = 0, cnt = 0;
> >>>  
> >>> +	/*
> >>> +	 * Let's flush node pages first to flush inline_data.
> >>> +	 * We'll actually guarantee everything below under f2fs_lock_all.
> >>> +	 */
> >>> +	f2fs_sync_node_pages(sbi, &wbc, false, false, FS_CP_NODE_IO);
> >>
> >> It is possible that user write a large number of inline data in between
> >> f2fs_sync_node_pages() and f2fs_lock_all(), it will cause the no-space issue in
> >> race condition.
> >>
> >> Also, if there is huge number of F2FS_DIRTY_IMETA, after this change, we will
> >> flush inode page twice which is unneeded.
> >>
> >> f2fs_sync_node_pages() --- flush dirty inode page
> >> f2fs_lock_all()
> >> ...
> >> f2fs_sync_inode_meta() --- update dirty inode page
> >> f2fs_sync_node_pages() --- flush dirty inode page again.
> >>
> > 
> > Another version:
> > 
> >>From 6b430b72af57c65c20dea7b87f7ba7e9df36be98 Mon Sep 17 00:00:00 2001
> > From: Sayali Lokhande <sayalil@xxxxxxxxxxxxxx>
> > Date: Thu, 30 Apr 2020 16:28:29 +0530
> > Subject: [PATCH] f2fs: Avoid double lock for cp_rwsem during checkpoint
> > 
> > There could be a scenario where f2fs_sync_node_pages gets
> > called during checkpoint, which in turn tries to flush
> > inline data and calls iput(). This results in deadlock as
> > iput() tries to hold cp_rwsem, which is already held at the
> > beginning by checkpoint->block_operations().
> > 
> > Call stack :
> > 
> > Thread A		Thread B
> > f2fs_write_checkpoint()
> > - block_operations(sbi)
> >  - f2fs_lock_all(sbi);
> >   - down_write(&sbi->cp_rwsem);
> > 
> >                         - open()
> >                          - igrab()
> >                         - write() write inline data
> >                         - unlink()
> > - f2fs_sync_node_pages()
> >  - if (is_inline_node(page))
> >   - flush_inline_data()
> >    - ilookup()
> >      page = f2fs_pagecache_get_page()
> >      if (!page)
> >       goto iput_out;
> >      iput_out:
> > 			-close()
> > 			-iput()
> >        iput(inode);
> >        - f2fs_evict_inode()
> >         - f2fs_truncate_blocks()
> >          - f2fs_lock_op()
> >            - down_read(&sbi->cp_rwsem);
> > 
> > Fixes: 2049d4fcb057 ("f2fs: avoid multiple node page writes due to inline_data")
> > Signed-off-by: Sayali Lokhande <sayalil@xxxxxxxxxxxxxx>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > ---
> >  fs/f2fs/checkpoint.c |  5 +++++
> >  fs/f2fs/f2fs.h       |  1 +
> >  fs/f2fs/node.c       | 51 ++++++++++++++++++++++++++++++++++++++++++--
> >  3 files changed, 55 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index d49f7a01d8a26..79e605f38f4fa 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1168,6 +1168,11 @@ static int block_operations(struct f2fs_sb_info *sbi)
> >  	};
> >  	int err = 0, cnt = 0;
> >  
> > +	/*
> > +	 * Let's flush inline_data in dirty node pages.
> > +	 */
> > +	f2fs_flush_inline_data(sbi);
> 
> Still there is a gap, user can write a large number of inline data here...

I think generic/204 is the case, and I don't hit a panic with this patch.

> 
> Would that be enough? I doubt we can suffer this issue in below pathes
> as well:

I don't think so, since iput is called after f2fs_unlock_all().

> 
> - block_operations
>  - f2fs_sync_dirty_inodes
>   - iput
>  - f2fs_sync_inode_meta
>   - iput
> 
> Thanks,
> 
> > +
> >  retry_flush_quotas:
> >  	f2fs_lock_all(sbi);
> >  	if (__need_flush_quota(sbi)) {
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 2a8ea81c52a15..7f3d259e7e376 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -3282,6 +3282,7 @@ void f2fs_ra_node_page(struct f2fs_sb_info *sbi, nid_t nid);
> >  struct page *f2fs_get_node_page(struct f2fs_sb_info *sbi, pgoff_t nid);
> >  struct page *f2fs_get_node_page_ra(struct page *parent, int start);
> >  int f2fs_move_node_page(struct page *node_page, int gc_type);
> > +int f2fs_flush_inline_data(struct f2fs_sb_info *sbi);
> >  int f2fs_fsync_node_pages(struct f2fs_sb_info *sbi, struct inode *inode,
> >  			struct writeback_control *wbc, bool atomic,
> >  			unsigned int *seq_id);
> > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > index 1db8cabf727ef..e632de10aedab 100644
> > --- a/fs/f2fs/node.c
> > +++ b/fs/f2fs/node.c
> > @@ -1807,6 +1807,53 @@ static bool flush_dirty_inode(struct page *page)
> >  	return true;
> >  }
> >  
> > +int f2fs_flush_inline_data(struct f2fs_sb_info *sbi)
> > +{
> > +	pgoff_t index = 0;
> > +	struct pagevec pvec;
> > +	int nr_pages;
> > +	int ret = 0;
> > +
> > +	pagevec_init(&pvec);
> > +
> > +	while ((nr_pages = pagevec_lookup_tag(&pvec,
> > +			NODE_MAPPING(sbi), &index, PAGECACHE_TAG_DIRTY))) {
> > +		int i;
> > +
> > +		for (i = 0; i < nr_pages; i++) {
> > +			struct page *page = pvec.pages[i];
> > +
> > +			if (!IS_DNODE(page))
> > +				continue;
> > +
> > +			lock_page(page);
> > +
> > +			if (unlikely(page->mapping != NODE_MAPPING(sbi))) {
> > +continue_unlock:
> > +				unlock_page(page);
> > +				continue;
> > +			}
> > +
> > +			if (!PageDirty(page)) {
> > +				/* someone wrote it for us */
> > +				goto continue_unlock;
> > +			}
> > +
> > +			/* flush inline_data, if it's async context. */
> > +			if (is_inline_node(page)) {
> > +				clear_inline_node(page);
> > +				unlock_page(page);
> > +				flush_inline_data(sbi, ino_of_node(page));
> > +				continue;
> > +			}
> > +			unlock_page(page);
> > +		}
> > +		pagevec_release(&pvec);
> > +		cond_resched();
> > +	}
> > +	return ret;
> > +}
> > +
> >  int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
> >  				struct writeback_control *wbc,
> >  				bool do_balance, enum iostat_type io_type)
> > @@ -1870,8 +1917,8 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
> >  				goto continue_unlock;
> >  			}
> >  
> > -			/* flush inline_data */
> > -			if (is_inline_node(page)) {
> > +			/* flush inline_data, if it's async context. */
> > +			if (do_balance && is_inline_node(page)) {
> >  				clear_inline_node(page);
> >  				unlock_page(page);
> >  				flush_inline_data(sbi, ino_of_node(page));
> >