Messages in this thread | | | Date | Fri, 14 Feb 2020 09:24:25 +0530 | From | Sahitya Tummala <> | Subject | Re: [PATCH] f2fs: fix the panic in do_checkpoint() |
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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.
> > > > > 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.
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); > > > >
-- -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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