Messages in this thread | | | Date | Wed, 2 Feb 2022 17:51:37 -0800 | From | Jaegeuk Kim <> | Subject | Re: [PATCH] f2fs: fix to avoid potential deadlock |
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On 01/29, Chao Yu wrote: > On 2022/1/29 8:37, Jaegeuk Kim wrote: > > 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? > > I'm not sure I've got your concern correctly... > > Do you mean NodeA and other IOs from do_writepages() were plugged in > different local plug variables?
I think so.
> > Thanks, > > > > > > > > > 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 <zhiguo.niu@unisoc.com> > > > > > Signed-off-by: Jing Xia <jing.xia@unisoc.com> > > > > > Signed-off-by: Chao Yu <chao@kernel.org> > > > > > --- > > > > > 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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