Re: [PATCH 1/2] f2fs: fix to commit bio cache after flushing node pages

[Jaegeuk Kim]

On Tue, Sep 27, 2016 at 10:09:03AM +0800, Chao Yu wrote:
> On 2016/9/27 9:39, Jaegeuk Kim wrote:
> > On Tue, Sep 27, 2016 at 08:57:41AM +0800, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2016/9/27 2:33, Jaegeuk Kim wrote:
> >>> Hi Chao,
> >>>
> >>> On Tue, Sep 27, 2016 at 12:09:52AM +0800, Chao Yu wrote:
> >>>> From: Chao Yu <yuchao0@xxxxxxxxxx>
> >>>>
> >>>> In sync_node_pages, we won't check and commit last merged pages in private
> >>>> bio cache of f2fs, as these pages were taged as writeback, someone who is
> >>>> waiting for writebacking of the page will be blocked until the cache was
> >>>> committed by someone else.
> >>>>
> >>>> We need to commit node type bio cache to avoid potential deadlock or long
> >>>> delay of waiting writeback.
> >>>>
> >>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> >>>> ---
> >>>>  fs/f2fs/node.c | 11 +++++++++--
> >>>>  1 file changed, 9 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> >>>> index 9faddcd..f73f774 100644
> >>>> --- a/fs/f2fs/node.c
> >>>> +++ b/fs/f2fs/node.c
> >>>> @@ -1416,6 +1416,7 @@ int sync_node_pages(struct f2fs_sb_info *sbi, struct writeback_control *wbc)
> >>>>  	struct pagevec pvec;
> >>>>  	int step = 0;
> >>>>  	int nwritten = 0;
> >>>> +	int ret = 0;
> >>>>  
> >>>>  	pagevec_init(&pvec, 0);
> >>>>  
> >>>> @@ -1436,7 +1437,8 @@ next_step:
> >>>>  
> >>>>  			if (unlikely(f2fs_cp_error(sbi))) {
> >>>>  				pagevec_release(&pvec);
> >>>> -				return -EIO;
> >>>> +				ret = -EIO;
> >>>> +				goto out;
> >>>>  			}
> >>>>  
> >>>>  			/*
> >>>> @@ -1487,6 +1489,8 @@ continue_unlock:
> >>>>  
> >>>>  			if (NODE_MAPPING(sbi)->a_ops->writepage(page, wbc))
> >>>>  				unlock_page(page);
> >>>> +			else
> >>>> +				nwritten++;
> >>>>  
> >>>>  			if (--wbc->nr_to_write == 0)
> >>>>  				break;
> >>>> @@ -1504,7 +1508,10 @@ continue_unlock:
> >>>>  		step++;
> >>>>  		goto next_step;
> >>>>  	}
> >>>> -	return nwritten;
> >>>> +out:
> >>>> +	if (nwritten)
> >>>> +		f2fs_submit_merged_bio(sbi, NODE, WRITE);
> >>>
> >>> IIRC, we don't need to flush this, since f2fs_submit_merged_bio_cond() would
> >>> handle this in f2fs_wait_on_page_writeback().
> >>
> >> Yes, it covers all the cases in f2fs private codes, but there are still some
> >> codes in mm or fs directory, and they didn't use f2fs_wait_on_page_writeback
> >> when waiting page writeback. Such as do_writepages && filemap_fdatawait in
> >> __writeback_single_inode...
> > 
> > The do_writepages() is okay, which will call f2fs_write_node_pages().
> > The __writeback_single_inode() won't do filemap_fdatawait() with WB_SYNC_ALL.
> > We don't need to take care of truncation as well.
> > 
> > Any missing one?
> 
> Another is: while testing with first version of checkpoint error injection, I
> encounter below dump stack:
> 
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> mount           D ffff8801c1bf7960     0 97685  97397 0x00080000
>  ffff8801c1bf7960 ffff8801c1bf7930 ffff880175900000 ffff8801c1bf7980
>  ffff8801c1bf8000 0000000000000000 7fffffffffffffff ffff88021f7be340
>  ffffffff817c8880 ffff8801c1bf7978 ffffffff817c80a5 ffff880214f58fc0
> Call Trace:
>  [<ffffffff817c8880>] ? bit_wait+0x50/0x50
>  [<ffffffff817c80a5>] schedule+0x35/0x80
>  [<ffffffff817cb152>] schedule_timeout+0x292/0x3d0
>  [<ffffffff81022ab5>] ? xen_clocksource_get_cycles+0x15/0x20
>  [<ffffffff810eeb5c>] ? ktime_get+0x3c/0xb0
>  [<ffffffff817c8880>] ? bit_wait+0x50/0x50
>  [<ffffffff817c7906>] io_schedule_timeout+0xa6/0x110
>  [<ffffffff817c889b>] bit_wait_io+0x1b/0x60
>  [<ffffffff817c84e4>] __wait_on_bit+0x64/0x90
>  [<ffffffff8117dcd4>] wait_on_page_bit+0xc4/0xd0
>  [<ffffffff810bc4d0>] ? autoremove_wake_function+0x40/0x40
>  [<ffffffff81190a29>] truncate_inode_pages_range+0x409/0x840
>  [<ffffffff811a406d>] ? pcpu_free_area+0x13d/0x1a0
>  [<ffffffff810bc025>] ? wake_up_bit+0x25/0x30
>  [<ffffffff81190ecc>] truncate_inode_pages_final+0x4c/0x60
>  [<ffffffffa025e9e8>] f2fs_evict_inode+0x48/0x390 [f2fs]
>  [<ffffffff812212f7>] evict+0xc7/0x1a0
>  [<ffffffff81221f77>] iput+0x197/0x200
>  [<ffffffffa0268242>] f2fs_fill_super+0xab2/0x1130 [f2fs]
>  [<ffffffff81209454>] mount_bdev+0x184/0x1c0
>  [<ffffffffa0267790>] ? f2fs_commit_super+0x100/0x100 [f2fs]
>  [<ffffffffa02646a5>] f2fs_mount+0x15/0x20 [f2fs]
>  [<ffffffff81209e19>] mount_fs+0x39/0x160
>  [<ffffffff81225e47>] vfs_kern_mount+0x67/0x110
>  [<ffffffff812283bb>] do_mount+0x1bb/0xc80
>  [<ffffffff81229163>] SyS_mount+0x83/0xd0
>  [<ffffffff8100391e>] do_syscall_64+0x6e/0x170
>  [<ffffffff817cc325>] entry_SYSCALL64_slow_path+0x25/0x25
> 
> Any thoughts?

I think this should not happen normally, since f2fs_stop_checkpoint() calls
f2fs_flush_merged_bios().

Thanks,

> 
> > 
> >>
> >> Thanks,
> >>
> >>>
> >>> Thanks,
> >>>
> >>>> +	return ret;
> >>>>  }
> >>>>  
> >>>>  int wait_on_node_pages_writeback(struct f2fs_sb_info *sbi, nid_t ino)
> >>>> -- 
> >>>> 2.7.2
> >>>
> >>> .
> >>>
> > 
> > .
> >