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

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Message-ID: <20200529223426.GA249109@google.com>
Date:   Fri, 29 May 2020 15:34:26 -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 05/29, 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.

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

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index ebbadde6cbced..f67cffc38975e 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -3095,6 +3095,14 @@ void f2fs_allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
 	struct curseg_info *curseg = CURSEG_I(sbi, type);
 	bool put_pin_sem = false;
 
+	/*
+	 * 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);
+
 	if (type == CURSEG_COLD_DATA) {
 		/* GC during CURSEG_COLD_DATA_PINNED allocation */
 		if (down_read_trylock(&sbi->pin_sem)) {
@@ -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