Messages in this thread Patch in this message | | | Date | Thu, 3 Feb 2022 22:57:51 +0800 | Subject | Re: [PATCH] f2fs: fix to avoid potential deadlock | From | Chao Yu <> |
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On 2022/2/3 9:51, Jaegeuk Kim wrote: > 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.
I guess block plug helper says it doesn't allow to use nested plug, so there is only one plug in kworker thread?
void blk_start_plug_nr_ios(struct blk_plug *plug, unsigned short nr_ios) { struct task_struct *tsk = current;
/* * If this is a nested plug, don't actually assign it. */ if (tsk->plug) return; ... }
Thanks,
> >> >> 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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