Messages in this thread | | | Date | Fri, 25 Feb 2022 11:02:05 +0800 | Subject | Re: [f2fs-dev] [PATCH] f2fs: fix to avoid potential deadlock | From | Chao Yu <> |
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On 2022/2/3 22:57, Chao Yu wrote: > 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; > ... > }
Any further comments?
Thanks,
> > 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 > > > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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