Messages in this thread | | | Subject | Re: [PATCH V4] f2fs: Avoid double lock for cp_rwsem during checkpoint | From | Chao Yu <> | Date | Sat, 9 May 2020 11:02:25 +0800 |
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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@kernel.org> > 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@codeaurora.org> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > --- > 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.
Since block_operations->f2fs_sync_inode_meta has synced inode cache to inode page, so in block_operations->f2fs_sync_node_pages, could we check nlink before flush_inline_data():
if (is_inline_node(page)) { if (IS_INODE(page) && raw_inode_page->i_links) { flush_inline_data() } }
> clear_inline_node(page); > unlock_page(page); > flush_inline_data(sbi, ino_of_node(page)); >
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