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

From: Chao Yu
Date: Mon May 26 2014 - 02:15:28 EST

Hi Kim,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> Sent: Wednesday, May 21, 2014 11:37 AM
> To: Chao Yu
> Cc: Jaegeuk Kim; 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
>
> 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;
> > + 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;

Agreed, it helps to remove a lot of redundant code here.
Thanks!

>
> 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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