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Subject[PATCH 3.16 042/148] quota: fix livelock in dquot_writeback_dquots
3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

commit 6ff33d99fc5c96797103b48b7b0902c296f09c05 upstream.

Write only quotas which are dirty at entry.

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

Link: https://lore.kernel.org/r/20191031103920.3919-1-dmonakhov@openvz.org
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/quota/dquot.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -607,7 +607,7 @@ 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;
@@ -620,9 +620,10 @@ int dquot_writeback_dquots(struct super_
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);
/* Dirty and inactive can be only bad dquot... */
if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) {
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