net/mlx5: Add a timeout to acquire the command queue semaphore

Prevent forced completion handling on an entry that has not yet been
assigned an index, causing an out of bounds access on idx = -22.
Instead of waiting indefinitely for the sem, blocking flow now waits for
index to be allocated or a sem acquisition timeout before beginning the
timer for FW completion.

Kernel log example:
mlx5_core 0000:06:00.0: wait_func_handle_exec_timeout:1128:(pid 185911): cmd[-22]: CREATE_UCTX(0xa04) No done completion

Fixes: 8e715cd6 ("net/mlx5: Set command entry semaphore up once got index free")
Signed-off-by: Akiva Goldberger <agoldberger@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/20240509112951.590184-5-tariqt@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/cmd.c

@@ -969,19 +969,32 @@ static void cmd_work_handler(struct work_struct *work)
 	bool poll_cmd = ent->polling;
 	struct mlx5_cmd_layout *lay;
 	struct mlx5_core_dev *dev;
-	unsigned long cb_timeout;
-	struct semaphore *sem;
+	unsigned long timeout;
 	unsigned long flags;
 	int alloc_ret;
 	int cmd_mode;
 
+	complete(&ent->handling);
+
 	dev = container_of(cmd, struct mlx5_core_dev, cmd);
-	cb_timeout = msecs_to_jiffies(mlx5_tout_ms(dev, CMD));
+	timeout = msecs_to_jiffies(mlx5_tout_ms(dev, CMD));
 
-	complete(&ent->handling);
-	sem = ent->page_queue ? &cmd->vars.pages_sem : &cmd->vars.sem;
-	down(sem);
 	if (!ent->page_queue) {
+		if (down_timeout(&cmd->vars.sem, timeout)) {
+			mlx5_core_warn(dev, "%s(0x%x) timed out while waiting for a slot.\n",
+				       mlx5_command_str(ent->op), ent->op);
+			if (ent->callback) {
+				ent->callback(-EBUSY, ent->context);
+				mlx5_free_cmd_msg(dev, ent->out);
+				free_msg(dev, ent->in);
+				cmd_ent_put(ent);
+			} else {
+				ent->ret = -EBUSY;
+				complete(&ent->done);
+			}
+			complete(&ent->slotted);
+			return;
+		}
 		alloc_ret = cmd_alloc_index(cmd, ent);
 		if (alloc_ret < 0) {
 			mlx5_core_err_rl(dev, "failed to allocate command entry\n");
@@ -994,10 +1007,11 @@ static void cmd_work_handler(struct work_struct *work)
 				ent->ret = -EAGAIN;
 				complete(&ent->done);
 			}
-			up(sem);
+			up(&cmd->vars.sem);
 			return;
 		}
 	} else {
+		down(&cmd->vars.pages_sem);
 		ent->idx = cmd->vars.max_reg_cmds;
 		spin_lock_irqsave(&cmd->alloc_lock, flags);
 		clear_bit(ent->idx, &cmd->vars.bitmask);
@@ -1005,6 +1019,8 @@ static void cmd_work_handler(struct work_struct *work)
 		spin_unlock_irqrestore(&cmd->alloc_lock, flags);
 	}
 
+	complete(&ent->slotted);
+
 	lay = get_inst(cmd, ent->idx);
 	ent->lay = lay;
 	memset(lay, 0, sizeof(*lay));
@@ -1023,7 +1039,7 @@ static void cmd_work_handler(struct work_struct *work)
 	ent->ts1 = ktime_get_ns();
 	cmd_mode = cmd->mode;
 
-	if (ent->callback && schedule_delayed_work(&ent->cb_timeout_work, cb_timeout))
+	if (ent->callback && schedule_delayed_work(&ent->cb_timeout_work, timeout))
 		cmd_ent_get(ent);
 	set_bit(MLX5_CMD_ENT_STATE_PENDING_COMP, &ent->state);
 
@@ -1143,6 +1159,9 @@ static int wait_func(struct mlx5_core_dev *dev, struct mlx5_cmd_work_ent *ent)
 		ent->ret = -ECANCELED;
 		goto out_err;
 	}
+
+	wait_for_completion(&ent->slotted);
+
 	if (cmd->mode == CMD_MODE_POLLING || ent->polling)
 		wait_for_completion(&ent->done);
 	else if (!wait_for_completion_timeout(&ent->done, timeout))
@@ -1157,6 +1176,9 @@ static int wait_func(struct mlx5_core_dev *dev, struct mlx5_cmd_work_ent *ent)
 	} else if (err == -ECANCELED) {
 		mlx5_core_warn(dev, "%s(0x%x) canceled on out of queue timeout.\n",
 			       mlx5_command_str(ent->op), ent->op);
+	} else if (err == -EBUSY) {
+		mlx5_core_warn(dev, "%s(0x%x) timeout while waiting for command semaphore.\n",
+			       mlx5_command_str(ent->op), ent->op);
 	}
 	mlx5_core_dbg(dev, "err %d, delivery status %s(%d)\n",
 		      err, deliv_status_to_str(ent->status), ent->status);
@@ -1208,6 +1230,7 @@ static int mlx5_cmd_invoke(struct mlx5_core_dev *dev, struct mlx5_cmd_msg *in,
 	ent->polling = force_polling;
 
 	init_completion(&ent->handling);
+	init_completion(&ent->slotted);
 	if (!callback)
 		init_completion(&ent->done);
 
@@ -1225,7 +1248,7 @@ static int mlx5_cmd_invoke(struct mlx5_core_dev *dev, struct mlx5_cmd_msg *in,
 		return 0; /* mlx5_cmd_comp_handler() will put(ent) */
 
 	err = wait_func(dev, ent);
-	if (err == -ETIMEDOUT || err == -ECANCELED)
+	if (err == -ETIMEDOUT || err == -ECANCELED || err == -EBUSY)
 		goto out_free;
 
 	ds = ent->ts2 - ent->ts1;

include/linux/mlx5/driver.h

@@ -862,6 +862,7 @@ struct mlx5_cmd_work_ent {
 	void		       *context;
 	int			idx;
 	struct completion	handling;
+	struct completion	slotted;
 	struct completion	done;
 	struct mlx5_cmd        *cmd;
 	struct work_struct	work;