Re: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files

[Jaegeuk Kim]

On 09/09, Chao Yu wrote:
> On 2019/9/9 16:21, Jaegeuk Kim wrote:
> > On 09/09, Chao Yu wrote:
> >> On 2019/9/9 16:01, Jaegeuk Kim wrote:
> >>> On 09/09, Chao Yu wrote:
> >>>> On 2019/9/9 15:30, Jaegeuk Kim wrote:
> >>>>> On 09/09, Chao Yu wrote:
> >>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote:
> >>>>>>> If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
> >>>>>>> get commited pages but atomic_file being still set like:
> >>>>>>>
> >>>>>>> - inmem:    0, atomic IO:    4 (Max.   10), volatile IO:    0 (Max.    0)
> >>>>>>>
> >>>>>>> If GC selects this block, we can get an infinite loop like this:
> >>>>>>>
> >>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>>
> >>>>>>> In that moment, we can observe:
> >>>>>>>
> >>>>>>> [Before]
> >>>>>>> Try to move 5084219 blocks (BG: 384508)
> >>>>>>>   - data blocks : 4962373 (274483)
> >>>>>>>   - node blocks : 121846 (110025)
> >>>>>>> Skipped : atomic write 4534686 (10)
> >>>>>>>
> >>>>>>> [After]
> >>>>>>> Try to move 5088973 blocks (BG: 384508)
> >>>>>>>   - data blocks : 4967127 (274483)
> >>>>>>>   - node blocks : 121846 (110025)
> >>>>>>> Skipped : atomic write 4539440 (10)
> >>>>>>>
> >>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>>>>>> ---
> >>>>>>>  fs/f2fs/file.c | 10 +++++-----
> >>>>>>>  1 file changed, 5 insertions(+), 5 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>>>>>> index 7ae2f3bd8c2f..68b6da734e5f 100644
> >>>>>>> --- a/fs/f2fs/file.c
> >>>>>>> +++ b/fs/f2fs/file.c
> >>>>>>> @@ -1997,11 +1997,11 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >>>>>>>  			goto err_out;
> >>>>>>>  
> >>>>>>>  		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
> >>>>>>> -		if (!ret) {
> >>>>>>> -			clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>> -			F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>> -			stat_dec_atomic_write(inode);
> >>>>>>> -		}
> >>>>>>> +
> >>>>>>> +		/* doesn't need to check error */
> >>>>>>> +		clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>> +		F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>> +		stat_dec_atomic_write(inode);
> >>>>>>
> >>>>>> If there are still valid atomic write pages linked in .inmem_pages, it may cause
> >>>>>> memory leak when we just clear FI_ATOMIC_FILE flag.
> >>>>>
> >>>>> f2fs_commit_inmem_pages() should have flushed them.
> >>>>
> >>>> Oh, we failed to flush its nodes.
> >>>>
> >>>> However we won't clear such info if we failed to flush inmen pages, it looks
> >>>> inconsistent.
> >>>>
> >>>> Any interface needed to drop inmem pages or clear ATOMIC_FILE flag in that two
> >>>> error path? I'm not very clear how sqlite handle such error.
> >>>
> >>> f2fs_drop_inmem_pages() did that, but not in this case.
> >>
> >> What I mean is, for any error returned from atomic_commit() interface, should
> >> userspace application handle it with consistent way, like trigger
> >> f2fs_drop_inmem_pages(), so we don't need to handle it inside atomic_commit().
> > 
> > f2fs_ioc_abort_volatile_write() will be triggered.
> 
> If userspace can do this, we can get rid of this patch, or am I missing sth?

We don't know when that will come. And, other threads are waiting for GC here.

> 
> - f2fs_ioc_abort_volatile_write
>  - f2fs_drop_inmem_pages
>   - clear_inode_flag(inode, FI_ATOMIC_FILE);
>   - fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
>   - stat_dec_atomic_write(inode);
> 
> > 
> >>
> >>>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>>
> >>>>>>
> >>>>>> So my question is why below logic didn't handle such condition well?
> >>>>>>
> >>>>>> f2fs_gc()
> >>>>>>
> >>>>>> 	if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> >>>>>> 		if (skipped_round <= MAX_SKIP_GC_COUNT ||
> >>>>>> 					skipped_round * 2 < round) {
> >>>>>> 			segno = NULL_SEGNO;
> >>>>>> 			goto gc_more;
> >>>>>> 		}
> >>>>>>
> >>>>>> 		if (first_skipped < last_skipped &&
> >>>>>> 				(last_skipped - first_skipped) >
> >>>>>> 						sbi->skipped_gc_rwsem) {
> >>>>>> 			f2fs_drop_inmem_pages_all(sbi, true);
> >>>>>
> >>>>> This is doing nothing, since f2fs_commit_inmem_pages() removed the inode
> >>>>> from inmem list.
> >>>>>
> >>>>>> 			segno = NULL_SEGNO;
> >>>>>> 			goto gc_more;
> >>>>>> 		}
> >>>>>> 		if (gc_type == FG_GC && !is_sbi_flag_set(sbi, SBI_CP_DISABLED))
> >>>>>> 			ret = f2fs_write_checkpoint(sbi, &cpc);
> >>>>>> 	}
> >>>>>>
> >>>>>>>  	} else {
> >>>>>>>  		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
> >>>>>>>  	}
> >>>>>>>
> >>>>> .
> >>>>>
> >>> .
> >>>
> > .
> >