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

Jaegeuk Kim
2020-05-11T22:11:04Z

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@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.
> >
> > 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@codeaurora.org>
> > 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@codeaurora.org>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> > 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@codeaurora.org>
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@codeaurora.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
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);
+
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));
--
2.26.2.645.ge9eca65c58-goog