netdev - [net 02/11] net/mlx5: Allow async trigger completion execution on single CPU systems

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Date:   Wed,  2 Nov 2022 23:55:38 -0700
From:   Saeed Mahameed <saeed@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     Saeed Mahameed <saeedm@...dia.com>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Roy Novich <royno@...dia.com>,
        Alexander Schmidt <alexschm@...ibm.com>,
        Moshe Shemesh <moshe@...dia.com>
Subject: [net 02/11] net/mlx5: Allow async trigger completion execution on single CPU systems

From: Roy Novich <royno@...dia.com>

For a single CPU system, the kernel thread executing mlx5_cmd_flush()
never releases the CPU but calls down_trylock(&cmd→sem) in a busy loop.
On a single processor system, this leads to a deadlock as the kernel
thread which executes mlx5_cmd_invoke() never gets scheduled. Fix this,
by adding the cond_resched() call to the loop, allow the command
completion kernel thread to execute.

Fixes: 8e715cd613a1 ("net/mlx5: Set command entry semaphore up once got index free")
Signed-off-by: Alexander Schmidt <alexschm@...ibm.com>
Signed-off-by: Roy Novich <royno@...dia.com>
Reviewed-by: Moshe Shemesh <moshe@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index 46ba4c2faad2..2e0d59ca62b5 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -1770,12 +1770,17 @@ void mlx5_cmd_flush(struct mlx5_core_dev *dev)
 	struct mlx5_cmd *cmd = &dev->cmd;
 	int i;
 
-	for (i = 0; i < cmd->max_reg_cmds; i++)
-		while (down_trylock(&cmd->sem))
+	for (i = 0; i < cmd->max_reg_cmds; i++) {
+		while (down_trylock(&cmd->sem)) {
 			mlx5_cmd_trigger_completions(dev);
+			cond_resched();
+		}
+	}
 
-	while (down_trylock(&cmd->pages_sem))
+	while (down_trylock(&cmd->pages_sem)) {
 		mlx5_cmd_trigger_completions(dev);
+		cond_resched();
+	}
 
 	/* Unlock cmdif */
 	up(&cmd->pages_sem);
-- 
2.38.1