Messages in this thread Patch in this message | | | Date | Sat, 29 Jan 2022 09:48:25 +0800 | Subject | Re: [PATCH] f2fs: fix to avoid potential deadlock | From | Chao Yu <> |
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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?
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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