linux-kernel - Re: [PATCH] Revert "f2fs: fix quota_sync failure due to f2fs_lock

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Message-ID: <20200530014926.GA39950@google.com>
Date:   Fri, 29 May 2020 18:49:26 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] Revert "f2fs: fix quota_sync failure due to f2fs_lock_op"

On 05/30, Chao Yu wrote:
> On 2020/5/30 6:34, Jaegeuk Kim wrote:
> > On 05/29, Chao Yu wrote:
> >> Under heavy fsstress, we may triggle panic while issuing discard,
> >> because __check_sit_bitmap() detects that discard command may earse
> >> valid data blocks, the root cause is as below race stack described,
> >> since we removed lock when flushing quota data, quota data writeback
> >> may race with write_checkpoint(), so that it causes inconsistency in
> >> between cached discard entry and segment bitmap.
> >>
> >> - f2fs_write_checkpoint
> >>  - block_operations
> >>   - set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH)
> >>  - f2fs_flush_sit_entries
> >>   - add_discard_addrs
> >>    - __set_bit_le(i, (void *)de->discard_map);
> >> 						- f2fs_write_data_pages
> >> 						 - f2fs_write_single_data_page
> >> 						   : inode is quota one, cp_rwsem won't be locked
> >> 						  - f2fs_do_write_data_page
> >> 						   - f2fs_allocate_data_block
> >> 						    - f2fs_wait_discard_bio
> >> 						      : discard entry has not been added yet.
> >> 						    - update_sit_entry
> >>  - f2fs_clear_prefree_segments
> >>   - f2fs_issue_discard
> >>   : add discard entry
> >>
> >> This patch fixes this issue by reverting 435cbab95e39 ("f2fs: fix quota_sync
> >> failure due to f2fs_lock_op").
> >>
> >> Fixes: 435cbab95e39 ("f2fs: fix quota_sync failure due to f2fs_lock_op")
> > 
> > The previous patch fixes quota_sync gets EAGAIN all the time.
> > How about this? It seems this works for fsstress test.
> > 

Then this?

---
 fs/f2fs/segment.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index ebbadde6cbced..ed11dcf2d69ed 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -3107,6 +3107,14 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 		type = CURSEG_COLD_DATA;
 	}
 
+	/*
+	 * We need to wait for node_write to avoid block allocation during
+	 * checkpoint. This can only happen to quota writes which can cause
+	 * the below discard race condition.
+	 */
+	if (IS_DATASEG(type))
+		down_write(&sbi->node_write);
+
 	down_read(&SM_I(sbi)->curseg_lock);
 
 	mutex_lock(&curseg->curseg_mutex);
@@ -3174,6 +3182,9 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 
 	if (put_pin_sem)
 		up_read(&sbi->pin_sem);
+
+	if (IS_DATASEG(type))
+		up_write(&sbi->node_write);
 }
 
 static void update_device_state(struct f2fs_io_info *fio)
-- 
2.27.0.rc0.183.gde8f92d652-goog