Messages in this thread | | | Subject | Re: [PATCH] f2fs: fix the panic in do_checkpoint() | From | Chao Yu <> | Date | Fri, 14 Feb 2020 15:16:59 +0800 |
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Hi Sahitya,
On 2020/2/14 11:54, Sahitya Tummala wrote: > Hi Chao, > > On Fri, Feb 14, 2020 at 10:26:18AM +0800, Chao Yu wrote: >> Hi Sahitya, >> >> On 2020/2/12 18:34, Sahitya Tummala wrote: >>> There could be a scenario where f2fs_sync_meta_pages() will not >>> ensure that all F2FS_DIRTY_META pages are submitted for IO. Thus, >>> resulting in the below panic in do_checkpoint() - >>> >>> f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) && >>> !f2fs_cp_error(sbi)); >>> >>> This can happen in a low-memory condition, where shrinker could >>> also be doing the writepage operation (stack shown below) >>> at the same time when checkpoint is running on another core. >>> >>> schedule >>> down_write >>> f2fs_submit_page_write -> by this time, this page in page cache is tagged >>> as PAGECACHE_TAG_WRITEBACK and PAGECACHE_TAG_DIRTY >>> is cleared, due to which f2fs_sync_meta_pages() >>> cannot sync this page in do_checkpoint() path. >>> f2fs_do_write_meta_page >>> __f2fs_write_meta_page >>> f2fs_write_meta_page >>> shrink_page_list >>> shrink_inactive_list >>> shrink_node_memcg >>> shrink_node >>> kswapd >> >> IMO, there may be one more simple fix here: >> >> - f2fs_do_write_meta_page(sbi, page, io_type); >> dec_page_count(sbi, F2FS_DIRTY_META); >> >> + f2fs_do_write_meta_page(sbi, page, io_type); >> >> If we can remove F2FS_DIRTY_META reference count before we clear >> PAGECACHE_TAG_DIRTY, we can avoid this race condition. >> >> - dec_page_count(sbi, F2FS_DIRTY_META); >> - f2fs_do_write_meta_page >> - set_page_writeback >> - __test_set_page_writeback >> - xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY); >> >> Thoughts? > > I believe it will be a problem because let's say the shrinker path is > still in the below stack - > > f2fs_submit_page_write(); > ->down_write(&io->io_rwsem); > > Then, the current f2fs_wait_on_all_pages_writeback() will not wait for > that page as it is not yet tagged as F2FS_WB_CP_DATA. Hence, the checkpoint > may proceed without waiting for this meta page to be written to disk.
Oh, you're right.
It looks the race can happen for data/node pages? like in fsync() procedure.
> >> >>> >>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org> >>> --- >>> fs/f2fs/checkpoint.c | 16 ++++++++-------- >>> fs/f2fs/f2fs.h | 2 +- >>> fs/f2fs/super.c | 2 +- >>> 3 files changed, 10 insertions(+), 10 deletions(-) >>> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c >>> index ffdaba0..2b651a3 100644 >>> --- a/fs/f2fs/checkpoint.c >>> +++ b/fs/f2fs/checkpoint.c >>> @@ -1250,14 +1250,14 @@ static void unblock_operations(struct f2fs_sb_info *sbi) >>> f2fs_unlock_all(sbi); >>> } >>> >>> -void f2fs_wait_on_all_pages_writeback(struct f2fs_sb_info *sbi) >>> +void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type) >>> { >>> DEFINE_WAIT(wait); >>> >>> for (;;) { >>> prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE); >>> >>> - if (!get_pages(sbi, F2FS_WB_CP_DATA)) >>> + if (!get_pages(sbi, type)) >>> break; >>> >>> if (unlikely(f2fs_cp_error(sbi))) >>> @@ -1384,8 +1384,8 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc) >>> >>> /* Flush all the NAT/SIT pages */ >>> f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO); >>> - f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) && >>> - !f2fs_cp_error(sbi)); >>> + /* Wait for all dirty meta pages to be submitted for IO */ >>> + f2fs_wait_on_all_pages(sbi, F2FS_DIRTY_META); >> >> I'm afraid calling f2fs_wait_on_all_pages() after we call >> f2fs_sync_meta_pages() is low efficient, as we only want to write out >> dirty meta pages instead of wait for writebacking them to device cache. >> > > I have modified the existing function f2fs_wait_on_all_pages_writeback() to > a generic one f2fs_wait_on_all_pages(), where it will wait according to the > requested type. In this case, it will only wait for dirty F2FS_DIRTY_META pages > but not for the writeback to device cache.
Oh, I see, as last dirty reference count decreaser won't wake up waiter, we need to wait for timeout, right? Can we decrease timeout count, maybe HZ/50 as we did for congestion.
io_schedule_timeout(5*HZ);
Thanks,
> > Thanks, > >> Thanks, >> >>> >>> /* >>> * modify checkpoint >>> @@ -1493,11 +1493,11 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc) >>> >>> /* Here, we have one bio having CP pack except cp pack 2 page */ >>> f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO); >>> - f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) && >>> - !f2fs_cp_error(sbi)); >>> + /* Wait for all dirty meta pages to be submitted for IO */ >>> + f2fs_wait_on_all_pages(sbi, F2FS_DIRTY_META); >>> >>> /* wait for previous submitted meta pages writeback */ >>> - f2fs_wait_on_all_pages_writeback(sbi); >>> + f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA); >>> >>> /* flush all device cache */ >>> err = f2fs_flush_device_cache(sbi); >>> @@ -1506,7 +1506,7 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc) >>> >>> /* barrier and flush checkpoint cp pack 2 page if it can */ >>> commit_checkpoint(sbi, ckpt, start_blk); >>> - f2fs_wait_on_all_pages_writeback(sbi); >>> + f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA); >>> >>> /* >>> * invalidate intermediate page cache borrowed from meta inode >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h >>> index 5a888a0..b0e0535 100644 >>> --- a/fs/f2fs/f2fs.h >>> +++ b/fs/f2fs/f2fs.h >>> @@ -3196,7 +3196,7 @@ bool f2fs_is_dirty_device(struct f2fs_sb_info *sbi, nid_t ino, >>> void f2fs_update_dirty_page(struct inode *inode, struct page *page); >>> void f2fs_remove_dirty_inode(struct inode *inode); >>> int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type); >>> -void f2fs_wait_on_all_pages_writeback(struct f2fs_sb_info *sbi); >>> +void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type); >>> int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc); >>> void f2fs_init_ino_entry_info(struct f2fs_sb_info *sbi); >>> int __init f2fs_create_checkpoint_caches(void); >>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c >>> index 5111e1f..084633b 100644 >>> --- a/fs/f2fs/super.c >>> +++ b/fs/f2fs/super.c >>> @@ -1105,7 +1105,7 @@ static void f2fs_put_super(struct super_block *sb) >>> /* our cp_error case, we can wait for any writeback page */ >>> f2fs_flush_merged_writes(sbi); >>> >>> - f2fs_wait_on_all_pages_writeback(sbi); >>> + f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA); >>> >>> f2fs_bug_on(sbi, sbi->fsync_node_num); >>> >>> >
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