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?
> - 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....@unisoc.com>
> Signed-off-by: Jing Xia <jing....@unisoc.com>
> Signed-off-by: Chao Yu <c...@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
