Re: [PATCH 2/2] xfs: fix unmount hang and memory leak on shutdown during quotaoff

Darrick J. Wong
2020-03-16T21:32:32Z

On Mon, Mar 16, 2020 at 01:00:32PM -0400, Brian Foster wrote:
> AIL removal of the quotaoff start intent and free of both quotaoff
> intents is currently limited to the ->iop_committed() handler of the
> end intent. This executes when the end intent is committed to the
> on-disk log and marks the completion of the operation. The problem
> with this is it assumes the success of the operation. If a shutdown
> or other error occurs during the quotaoff, it's possible for the
> quotaoff task to exit without removing the start intent from the
> AIL. This results in an unmount hang as the AIL cannot be emptied.
> Further, no other codepath frees the intents and so this is also a
> memory leak vector.

And I'm guessing that you'd rather we taught the quota items to be
self-releasing under error rather than making the quotaoff code be smart
enough to free the quotaoff-start item?

> First, update the high level quotaoff error path to directly remove
> and free the quotaoff start intent if it still exists in the AIL at
> the time of the error. Next, update both of the start and end
> quotaoff intents with an ->iop_release() callback to properly handle
> transaction abort.

I wonder, does this mean that we can drop the if (->io_release) check in
xfs_trans_free_items? ISTR we were wondering at one point if there ever
was a real use case for items that don't have a release function.

> This means that If the quotaoff start transaction aborts, it frees
> the start intent in the transaction commit path. If the filesystem
> shuts down before the end transaction allocates, the quotaoff
> sequence removes and frees the start intent. If the end transaction
> aborts, it removes the start intent and frees both. This ensures
> that a shutdown does not result in a hung unmount and that memory is
> not leaked regardless of when a quotaoff error occurs.
>
> Signed-off-by: Brian Foster <bfoster@redhat.com>

FWIW, the code looks reasonable.

--D

> ---
> fs/xfs/xfs_dquot_item.c | 15 +++++++++++++++
> fs/xfs/xfs_qm_syscalls.c | 13 +++++++------
> 2 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
> index 2b816e9b4465..cf65e2e43c6e 100644
> --- a/fs/xfs/xfs_dquot_item.c
> +++ b/fs/xfs/xfs_dquot_item.c
> @@ -315,17 +315,32 @@ xfs_qm_qoffend_logitem_committed(
> return (xfs_lsn_t)-1;
> }
>
> +STATIC void
> +xfs_qm_qoff_logitem_release(
> + struct xfs_log_item *lip)
> +{
> + struct xfs_qoff_logitem *qoff = QOFF_ITEM(lip);
> +
> + if (test_bit(XFS_LI_ABORTED, &lip->li_flags)) {
> + if (qoff->qql_start_lip)
> + xfs_qm_qoff_logitem_relse(qoff->qql_start_lip);
> + xfs_qm_qoff_logitem_relse(qoff);
> + }
> +}
> +
> static const struct xfs_item_ops xfs_qm_qoffend_logitem_ops = {
> .iop_size = xfs_qm_qoff_logitem_size,
> .iop_format = xfs_qm_qoff_logitem_format,
> .iop_committed = xfs_qm_qoffend_logitem_committed,
> .iop_push = xfs_qm_qoff_logitem_push,
> + .iop_release = xfs_qm_qoff_logitem_release,
> };
>
> static const struct xfs_item_ops xfs_qm_qoff_logitem_ops = {
> .iop_size = xfs_qm_qoff_logitem_size,
> .iop_format = xfs_qm_qoff_logitem_format,
> .iop_push = xfs_qm_qoff_logitem_push,
> + .iop_release = xfs_qm_qoff_logitem_release,
> };
>
> /*
> diff --git a/fs/xfs/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
> index 1ea82764bf89..5d5ac65aa1cc 100644
> --- a/fs/xfs/xfs_qm_syscalls.c
> +++ b/fs/xfs/xfs_qm_syscalls.c
> @@ -29,8 +29,6 @@ xfs_qm_log_quotaoff(
> int error;
> struct xfs_qoff_logitem *qoffi;
>
> - *qoffstartp = NULL;
> -
> error = xfs_trans_alloc(mp, &M_RES(mp)->tr_qm_quotaoff, 0, 0, 0, &tp);
> if (error)
> goto out;
> @@ -62,7 +60,7 @@ xfs_qm_log_quotaoff(
> STATIC int
> xfs_qm_log_quotaoff_end(
> struct xfs_mount *mp,
> - struct xfs_qoff_logitem *startqoff,
> + struct xfs_qoff_logitem **startqoff,
> uint flags)
> {
> struct xfs_trans *tp;
> @@ -73,9 +71,10 @@ xfs_qm_log_quotaoff_end(
> if (error)
> return error;
>
> - qoffi = xfs_trans_get_qoff_item(tp, startqoff,
> + qoffi = xfs_trans_get_qoff_item(tp, *startqoff,
> flags & XFS_ALL_QUOTA_ACCT);
> xfs_trans_log_quotaoff_item(tp, qoffi);
> + *startqoff = NULL;
>
> /*
> * We have to make sure that the transaction is secure on disk before we
> @@ -103,7 +102,7 @@ xfs_qm_scall_quotaoff(
> uint dqtype;
> int error;
> uint inactivate_flags;
> - struct xfs_qoff_logitem *qoffstart;
> + struct xfs_qoff_logitem *qoffstart = NULL;
>
> /*
> * No file system can have quotas enabled on disk but not in core.
> @@ -228,7 +227,7 @@ xfs_qm_scall_quotaoff(
> * So, we have QUOTAOFF start and end logitems; the start
> * logitem won't get overwritten until the end logitem appears...
> */
> - error = xfs_qm_log_quotaoff_end(mp, qoffstart, flags);
> + error = xfs_qm_log_quotaoff_end(mp, &qoffstart, flags);
> if (error) {
> /* We're screwed now. Shutdown is the only option. */
> xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> @@ -261,6 +260,8 @@ xfs_qm_scall_quotaoff(
> }
>
> out_unlock:
> + if (error && qoffstart)
> + xfs_qm_qoff_logitem_relse(qoffstart);
> mutex_unlock(&q->qi_quotaofflock);
> return error;
> }
> --
> 2.21.1
>