On Wed, 2023-02-08 at 15:09 -0500, David Jeffery wrote:
> If an admin connects an iscsi initiator to an iscsi target on the
> same
> system, the iscsi connection is vulnerable to deadlocks during memory
> allocations. Memory allocations in the target task accepting the I/O
> from
> the initiator can wait on the initiator's I/O when the system is
> under
> memory pressure, causing a deadlock situation between the iscsi
> target and
> initiator.
>
> When in this configuration, the deadlock scenario can be avoided by
> use of
> GFP_NOIO allocations. Rather than force all configurations to use
> NOIO,
> memalloc_noio_save/restore can be used to force GFP_NOIO allocations
> only
> when in this loopback configuration.
>
> Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
> ---
> drivers/target/iscsi/iscsi_target.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/drivers/target/iscsi/iscsi_target.c
> b/drivers/target/iscsi/iscsi_target.c
> index baf4da7bb3b4..a68e47e2cdf9 100644
> --- a/drivers/target/iscsi/iscsi_target.c
> +++ b/drivers/target/iscsi/iscsi_target.c
> @@ -16,6 +16,7 @@
> #include <linux/vmalloc.h>
> #include <linux/idr.h>
> #include <linux/delay.h>
> +#include <linux/sched/mm.h>
> #include <linux/sched/signal.h>
> #include <asm/unaligned.h>
> #include <linux/inet.h>
> @@ -4168,7 +4169,10 @@ int iscsi_target_rx_thread(void *arg)
> {
> int rc;
> struct iscsit_conn *conn = arg;
> + struct dst_entry *dst;
> bool conn_freed = false;
> + bool loopback = false;
> + unsigned int flags;
>
> /*
> * Allow ourselves to be interrupted by SIGINT so that a
> @@ -4186,8 +4190,25 @@ int iscsi_target_rx_thread(void *arg)
> if (!conn->conn_transport->iscsit_get_rx_pdu)
> return 0;
>
> + /*
> + * If the iscsi connection is over a loopback device from using
> + * iscsi and iscsit on the same system, we need to set
> memalloc_noio to
> + * prevent memory allocation deadlocks between target and
> initiator.
> + */
> + rcu_read_lock();
> + dst = rcu_dereference(conn->sock->sk->sk_dst_cache);
> + if (dst && dst->dev && dst->dev->flags & IFF_LOOPBACK)
> + loopback = true;
> + rcu_read_unlock();
> +
> + if (loopback)
> + flags = memalloc_noio_save();
> +
> conn->conn_transport->iscsit_get_rx_pdu(conn);
>
> + if (loopback)
> + memalloc_noio_restore(flags);
> +
> if (!signal_pending(current))
> atomic_set(&conn->transport_failed, 1);
> iscsit_take_action_for_connection_exit(conn, &conn_freed);
I had mentioned to Mike that this was already tested at a large
customer and in our labs and resolved the deadlocks .
Regards
Laurence Oberman
