linux-kernel - [PATCH] f2fs: let background GC being aware of freezing

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Date:   Fri, 21 Jul 2017 11:36:35 +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: let background GC being aware of freezing

When ->freeze_fs is called from lvm for doing snapshot, it needs to
make sure there will be no more changes in filesystem's data, however,
previously, background GC wasn't aware of freezing, so in environment
with active background GC thread, data of snapshot becomes unstable.

This patch fixes this issue by adding sb_{start,end}_intwrite in GC
flow.

Signed-off-by: Chao Yu <yuchao0@...wei.com>
---
 fs/f2fs/gc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 76ad2c3d88db..1c0117f60083 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -55,6 +55,8 @@ static int gc_thread_func(void *data)
 		}
 #endif
 
+		sb_start_intwrite(sbi->sb);
+
 		/*
 		 * [GC triggering condition]
 		 * 0. GC is not conducted currently.
@@ -69,12 +71,12 @@ static int gc_thread_func(void *data)
 		 * So, I'd like to wait some time to collect dirty segments.
 		 */
 		if (!mutex_trylock(&sbi->gc_mutex))
-			continue;
+			goto next;
 
 		if (!is_idle(sbi)) {
 			increase_sleep_time(gc_th, &wait_ms);
 			mutex_unlock(&sbi->gc_mutex);
-			continue;
+			goto next;
 		}
 
 		if (has_enough_invalid_blocks(sbi))
@@ -93,6 +95,8 @@ static int gc_thread_func(void *data)
 
 		/* balancing f2fs's metadata periodically */
 		f2fs_balance_fs_bg(sbi);
+next:
+		sb_end_intwrite(sbi->sb);
 
 	} while (!kthread_should_stop());
 	return 0;
-- 
2.13.1.388.g69e6b9b4f4a9