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    Subject[PATCH 4.9 146/199] quota: fix livelock in dquot_writeback_dquots
    Date
    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
    CC: stable@vger.kernel.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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/quota/dquot.c | 9 +++++----
    1 file changed, 5 insertions(+), 4 deletions(-)

    --- a/fs/quota/dquot.c
    +++ b/fs/quota/dquot.c
    @@ -611,7 +611,7 @@ 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;
    @@ -624,9 +624,10 @@ 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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