Messages in this thread | | | Date | Fri, 28 Jan 2022 09:43:27 +0800 | Subject | Re: [PATCH] f2fs: fix to avoid potential deadlock | From | Chao Yu <> |
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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)?
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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