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

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Date:   Mon,  9 Sep 2019 02:25:32 +0100
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files

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@...nel.org>
---
 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);
 	} else {
 		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
 	}
-- 
2.19.0.605.g01d371f741-goog