On 01/28, Chao Yu wrote:
> On 2022/1/28 5:59, Jaegeuk Kim wrote:
> > On 01/27, Chao Yu wrote:
> > > Quoted from Jing Xia's report, there is a potential deadlock may happen
> > > between kworker and checkpoint as below:
> > >
> > > [T:writeback] [T:checkpoint]
> > > - wb_writeback
> > > - blk_start_plug
> > > bio contains NodeA was plugged in writeback threads
> >
> > I'm still trying to understand more precisely. So, how is it possible to
> > have bio having node write in this current context?
>
> IMO, after above blk_start_plug(), it may plug some inode's node page in
> kworker
> during writebacking node_inode's data page (which should be node page)?
Wasn't that added into a different task->plug?
>
> Thanks,
>
> >
> > > - do_writepages -- sync write inodeB,
> > > inc wb_sync_req[DATA]
> > > - f2fs_write_data_pages
> > > - f2fs_write_single_data_page --
> > > write last dirty page
> > > - f2fs_do_write_data_page
> > > - set_page_writeback -- clear page
> > > dirty flag and
> > > PAGECACHE_TAG_DIRTY tag in radix
> > > tree
> > > - f2fs_outplace_write_data
> > > - f2fs_update_data_blkaddr
> > > - f2fs_wait_on_page_writeback --
> > > wait NodeA to writeback here
> > > - inode_dec_dirty_pages
> > > - writeback_sb_inodes
> > > - writeback_single_inode
> > > - do_writepages
> > > - f2fs_write_data_pages -- skip writepages due to wb_sync_req[DATA]
> > > - wbc->pages_skipped += get_dirty_pages() -- PAGECACHE_TAG_DIRTY is
> > > not set but get_dirty_pages() returns one
> > > - requeue_inode -- requeue inode to wb->b_dirty queue due to
> > > non-zero.pages_skipped
> > > - blk_finish_plug
> > >
> > > Let's try to avoid deadlock condition by forcing unplugging previous bio
> > > via
> > > blk_finish_plug(current->plug) once we'v skipped writeback in writepages()
> > > due to valid sbi->wb_sync_req[DATA/NODE].
> > >
> > > Fixes: 687de7f1010c ("f2fs: avoid IO split due to mixed WB_SYNC_ALL and
> > > WB_SYNC_NONE")
> > > Signed-off-by: Zhiguo Niu <[email protected]>
> > > Signed-off-by: Jing Xia <[email protected]>
> > > Signed-off-by: Chao Yu <[email protected]>
> > > ---
> > > fs/f2fs/data.c | 6 +++++-
> > > fs/f2fs/node.c | 6 +++++-
> > > 2 files changed, 10 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > > index 76d6fe7b0c8f..932a4c81acaf 100644
> > > --- a/fs/f2fs/data.c
> > > +++ b/fs/f2fs/data.c
> > > @@ -3174,8 +3174,12 @@ static int __f2fs_write_data_pages(struct
> > > address_space *mapping,
> > > /* to avoid spliting IOs due to mixed WB_SYNC_ALL and
> > > WB_SYNC_NONE */
> > > if (wbc->sync_mode == WB_SYNC_ALL)
> > > atomic_inc(&sbi->wb_sync_req[DATA]);
> > > - else if (atomic_read(&sbi->wb_sync_req[DATA]))
> > > + else if (atomic_read(&sbi->wb_sync_req[DATA])) {
> > > + /* to avoid potential deadlock */
> > > + if (current->plug)
> > > + blk_finish_plug(current->plug);
> > > goto skip_write;
> > > + }
> > > if (__should_serialize_io(inode, wbc)) {
> > > mutex_lock(&sbi->writepages);
> > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> > > index 556fcd8457f3..69c6bcaf5aae 100644
> > > --- a/fs/f2fs/node.c
> > > +++ b/fs/f2fs/node.c
> > > @@ -2106,8 +2106,12 @@ static int f2fs_write_node_pages(struct
> > > address_space *mapping,
> > > if (wbc->sync_mode == WB_SYNC_ALL)
> > > atomic_inc(&sbi->wb_sync_req[NODE]);
> > > - else if (atomic_read(&sbi->wb_sync_req[NODE]))
> > > + else if (atomic_read(&sbi->wb_sync_req[NODE])) {
> > > + /* to avoid potential deadlock */
> > > + if (current->plug)
> > > + blk_finish_plug(current->plug);
> > > goto skip_write;
> > > + }
> > > trace_f2fs_writepages(mapping->host, wbc, NODE);
> > > --
> > > 2.32.0
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