linux-kernel - [PATCH] f2fs: fix to avoid deadloop in foreground GC

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Message-ID: <20190410104550.82389-1-yuchao0@huawei.com>
Date:   Wed, 10 Apr 2019 18:45:50 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>,
        Chao Yu <yuchao0@...wei.com>
Subject: [PATCH] f2fs: fix to avoid deadloop in foreground GC

As Jungyeon reported in bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=203211

- Overview
When mounting the attached crafted image and making a new file, I got this error and the error messages keep repeating.

The image is intentionally fuzzed from a normal f2fs image for testing and I run with option CONFIG_F2FS_CHECK_FS on.

- Reproduces
mkdir test
mount -t f2fs tmp.img test
cd test
touch t

- Messages
[   58.820451] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.821485] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.822530] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.823571] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.824616] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.825640] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.826663] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.827698] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.828719] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.829759] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.830783] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.831828] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.832869] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.833888] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.834945] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.835996] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.837028] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.838051] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.839072] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.840100] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.841147] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.842186] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.843214] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.844267] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.845282] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.846305] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
[   58.847341] F2FS-fs (sdb): Inconsistent segment (1) type [1, 0] in SSA and SIT
... (repeating)

During GC, if segment type stored in SSA and SIT is inconsistent, we just
skip migrating current segment directly, since we need to know the exact
type to decide the migration function we use.

So in foreground GC, we will easily run into a infinite loop as we may
select the same victim segment which has inconsistent type due to greedy
policy. In order to end up this, we choose to shutdown filesystem. For
backgrond GC, we need to do that as well, so that we can avoid latter
potential infinite looped foreground GC.

Signed-off-by: Chao Yu <yuchao0@...wei.com>
---
 fs/f2fs/gc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index ab764bd106de..a66a8752e5f6 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1175,6 +1175,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
 				"type [%d, %d] in SSA and SIT",
 				segno, type, GET_SUM_TYPE((&sum->footer)));
 			set_sbi_flag(sbi, SBI_NEED_FSCK);
+			f2fs_stop_checkpoint(sbi, false);
 			goto skip;
 		}
 
-- 
2.18.0.rc1