RE: [f2fs-dev] [PATCH] f2fs: avoid crash when trace f2fs_submit_page_mbio event in ra_sum_pages

[Chao Yu]

Hi changman,

> -----Original Message-----
> From: Changman Lee [mailto:cm224.lee@xxxxxxxxxxx]
> Sent: Friday, May 23, 2014 1:14 PM
> To: Jaegeuk Kim
> Cc: Chao Yu; linux-fsdevel@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid crash when trace f2fs_submit_page_mbio event in
> ra_sum_pages
> 
> On Wed, May 21, 2014 at 12:36:46PM +0900, Jaegeuk Kim wrote:
> > Hi Chao,
> >
> > 2014-05-16 (ê), 17:14 +0800, Chao Yu:
> > > Previously we allocate pages with no mapping in ra_sum_pages(), so we may
> > > encounter a crash in event trace of f2fs_submit_page_mbio where we access
> > > mapping data of the page.
> > >
> > > We'd better allocate pages in bd_inode mapping and invalidate these pages after
> > > we restore data from pages. It could avoid crash in above scenario.
> > >
> > > Call Trace:
> > >  [<f1031630>] ? ftrace_raw_event_f2fs_write_checkpoint+0x80/0x80 [f2fs]
> > >  [<f10377bb>] f2fs_submit_page_mbio+0x1cb/0x200 [f2fs]
> > >  [<f103c5da>] restore_node_summary+0x13a/0x280 [f2fs]
> > >  [<f103e22d>] build_curseg+0x2bd/0x620 [f2fs]
> > >  [<f104043b>] build_segment_manager+0x1cb/0x920 [f2fs]
> > >  [<f1032c85>] f2fs_fill_super+0x535/0x8e0 [f2fs]
> > >  [<c115b66a>] mount_bdev+0x16a/0x1a0
> > >  [<f102f63f>] f2fs_mount+0x1f/0x30 [f2fs]
> > >  [<c115c096>] mount_fs+0x36/0x170
> > >  [<c1173635>] vfs_kern_mount+0x55/0xe0
> > >  [<c1175388>] do_mount+0x1e8/0x900
> > >  [<c1175d72>] SyS_mount+0x82/0xc0
> > >  [<c16059cc>] sysenter_do_call+0x12/0x22
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@xxxxxxxxxxx>
> > > ---
> > >  fs/f2fs/node.c |   49 ++++++++++++++++++++++++++++---------------------
> > >  1 file changed, 28 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > > index 3d60d3d..b5cd814 100644
> > > --- a/fs/f2fs/node.c
> > > +++ b/fs/f2fs/node.c
> > > @@ -1658,13 +1658,16 @@ int recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)
> > >
> > >  /*
> > >   * ra_sum_pages() merge contiguous pages into one bio and submit.
> > > - * these pre-readed pages are linked in pages list.
> > > + * these pre-readed pages are alloced in bd_inode's mapping tree.
> > >   */
> > > -static int ra_sum_pages(struct f2fs_sb_info *sbi, struct list_head *pages,
> > > +static int ra_sum_pages(struct f2fs_sb_info *sbi, struct page **pages,
> > >  				int start, int nrpages)
> > >  {
> > >  	struct page *page;
> > > +	struct inode *inode = sbi->sb->s_bdev->bd_inode;
> 
> How about use sbi->meta_inode instead of bd_inode, then we can do
> caching summary pages for further i/o.

In my understanding, In ra_sum_pages() we readahead node pages in NODE segment,
then we could padding current summary caching with nid of node page's footer.
So we should not cache this readaheaded pages in meta_inode's mapping.
Do I miss something?

Regards

> 
> > > +	struct address_space *mapping = inode->i_mapping;
> > >  	int page_idx = start;
> > > +	int alloced, readed;
> > >  	struct f2fs_io_info fio = {
> > >  		.type = META,
> > >  		.rw = READ_SYNC | REQ_META | REQ_PRIO
> > > @@ -1672,21 +1675,23 @@ static int ra_sum_pages(struct f2fs_sb_info *sbi, struct list_head
> *pages,
> > >
> > >  	for (; page_idx < start + nrpages; page_idx++) {
> > >  		/* alloc temporal page for read node summary info*/
> > > -		page = alloc_page(GFP_F2FS_ZERO);
> > > +		page = grab_cache_page(mapping, page_idx);
> > >  		if (!page)
> > >  			break;
> > > -
> > > -		lock_page(page);
> > > -		page->index = page_idx;
> > > -		list_add_tail(&page->lru, pages);
> > > +		page_cache_release(page);
> >
> > IMO, we don't need to do like this.
> > Instead,
> > 	for() {
> > 		page = grab_cache_page();
> > 		if (!page)
> > 			break;
> > 		page[page_idx] = page;
> > 		f2fs_submit_page_mbio(sbi, page, &fio);
> > 	}
> > 	f2fs_submit_merged_bio(sbi, META, READ);
> > 	return page_idx - start;
> >
> > Afterwards, in restore_node_summry(),
> > 	lock_page() will wait the end_io for read.
> > 	...
> > 	f2fs_put_page(pages[index], 1);
> >
> > Thanks,
> >
> > >  	}
> > >
> > > -	list_for_each_entry(page, pages, lru)
> > > -		f2fs_submit_page_mbio(sbi, page, page->index, &fio);
> > > +	alloced = page_idx - start;
> > > +	readed = find_get_pages_contig(mapping, start, alloced, pages);
> > > +	BUG_ON(alloced != readed);
> > > +
> > > +	for (page_idx = 0; page_idx < readed; page_idx++)
> > > +		f2fs_submit_page_mbio(sbi, pages[page_idx],
> > > +					pages[page_idx]->index, &fio);
> > >
> > >  	f2fs_submit_merged_bio(sbi, META, READ);
> > >
> > > -	return page_idx - start;
> > > +	return readed;
> > >  }
> > >
> > >  int restore_node_summary(struct f2fs_sb_info *sbi,
> > > @@ -1694,11 +1699,11 @@ int restore_node_summary(struct f2fs_sb_info *sbi,
> > >  {
> > >  	struct f2fs_node *rn;
> > >  	struct f2fs_summary *sum_entry;
> > > -	struct page *page, *tmp;
> > > +	struct inode *inode = sbi->sb->s_bdev->bd_inode;
> > >  	block_t addr;
> > >  	int bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
> > > -	int i, last_offset, nrpages, err = 0;
> > > -	LIST_HEAD(page_list);
> > > +	struct page *pages[bio_blocks];
> > > +	int i, index, last_offset, nrpages, err = 0;
> > >
> > >  	/* scan the node segment */
> > >  	last_offset = sbi->blocks_per_seg;
> > > @@ -1709,29 +1714,31 @@ int restore_node_summary(struct f2fs_sb_info *sbi,
> > >  		nrpages = min(last_offset - i, bio_blocks);
> > >
> > >  		/* read ahead node pages */
> > > -		nrpages = ra_sum_pages(sbi, &page_list, addr, nrpages);
> > > +		nrpages = ra_sum_pages(sbi, pages, addr, nrpages);
> > >  		if (!nrpages)
> > >  			return -ENOMEM;
> > >
> > > -		list_for_each_entry_safe(page, tmp, &page_list, lru) {
> > > +		for (index = 0; index < nrpages; index++) {
> > >  			if (err)
> > >  				goto skip;
> > >
> > > -			lock_page(page);
> > > -			if (unlikely(!PageUptodate(page))) {
> > > +			lock_page(pages[index]);
> > > +			if (unlikely(!PageUptodate(pages[index]))) {
> > >  				err = -EIO;
> > >  			} else {
> > > -				rn = F2FS_NODE(page);
> > > +				rn = F2FS_NODE(pages[index]);
> > >  				sum_entry->nid = rn->footer.nid;
> > >  				sum_entry->version = 0;
> > >  				sum_entry->ofs_in_node = 0;
> > >  				sum_entry++;
> > >  			}
> > > -			unlock_page(page);
> > > +			unlock_page(pages[index]);
> > >  skip:
> > > -			list_del(&page->lru);
> > > -			__free_pages(page, 0);
> > > +			page_cache_release(pages[index]);
> > >  		}
> > > +
> > > +		invalidate_mapping_pages(inode->i_mapping, addr,
> > > +							addr + nrpages);
> > >  	}
> > >  	return err;
> > >  }
> >
> > --
> > Jaegeuk Kim
> 
> 
> 
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