linux-ext4 - [PATCH 1/2] fs/quota: fix livelock in dquot_writeback

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Date:   Thu, 31 Oct 2019 10:39:19 +0000
From:   Dmitry Monakhov <dmonakhov@...nvz.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-ext4@...r.kernel.org, jack@...e.cz,
        Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Subject: [PATCH 1/2] fs/quota: fix livelock in dquot_writeback_dquots

From: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>

Write only quotas which are dirty at entry.


XFSTEST: https://github.com/dmonakhov/xfstests/commit/b10ad23566a5bf75832a6f500e1236084083cddc

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
---
 fs/quota/dquot.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 26812a6..b492b9e 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -622,7 +622,7 @@ EXPORT_SYMBOL(dquot_scan_active);
 /* Write all dquot structures to quota files */
 int dquot_writeback_dquots(struct super_block *sb, int type)
 {
-	struct list_head *dirty;
+	struct list_head dirty;
 	struct dquot *dquot;
 	struct quota_info *dqopt = sb_dqopt(sb);
 	int cnt;
@@ -636,9 +636,10 @@ int dquot_writeback_dquots(struct super_block *sb, int type)
 		if (!sb_has_quota_active(sb, cnt))
 			continue;
 		spin_lock(&dq_list_lock);
-		dirty = &dqopt->info[cnt].dqi_dirty_list;
-		while (!list_empty(dirty)) {
-			dquot = list_first_entry(dirty, struct dquot,
+		/* Move list away to avoid livelock. */
+		list_replace_init(&dqopt->info[cnt].dqi_dirty_list, &dirty);
+		while (!list_empty(&dirty)) {
+			dquot = list_first_entry(&dirty, struct dquot,
 						 dq_dirty);
 
 			WARN_ON(!test_bit(DQ_ACTIVE_B, &dquot->dq_flags));
-- 
2.7.4