linux-kernel - [PATCH 5.8 087/124] net/mlx5: Add retry mechanism to the command entry index allocation

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Message-Id: <20201012133151.073837836@linuxfoundation.org>
Date:   Mon, 12 Oct 2020 15:31:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eran Ben Elisha <eranbe@...dia.com>,
        Moshe Shemesh <moshe@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.8 087/124] net/mlx5: Add retry mechanism to the command entry index allocation

From: Eran Ben Elisha <eranbe@...dia.com>

[ Upstream commit 410bd754cd73c4a2ac3856d9a03d7b08f9c906bf ]

It is possible that new command entry index allocation will temporarily
fail. The new command holds the semaphore, so it means that a free entry
should be ready soon. Add one second retry mechanism before returning an
error.

Patch "net/mlx5: Avoid possible free of command entry while timeout comp
handler" increase the possibility to bump into this temporarily failure
as it delays the entry index release for non-callback commands.

Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB adapters")
Signed-off-by: Eran Ben Elisha <eranbe@...dia.com>
Reviewed-by: Moshe Shemesh <moshe@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/ethernet/mellanox/mlx5/core/cmd.c | 21 ++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index 37dae95e61d5f..2b597ac365f84 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
@@ -883,6 +883,25 @@ static bool opcode_allowed(struct mlx5_cmd *cmd, u16 opcode)
 	return cmd->allowed_opcode == opcode;
 }
 
+static int cmd_alloc_index_retry(struct mlx5_cmd *cmd)
+{
+	unsigned long alloc_end = jiffies + msecs_to_jiffies(1000);
+	int idx;
+
+retry:
+	idx = cmd_alloc_index(cmd);
+	if (idx < 0 && time_before(jiffies, alloc_end)) {
+		/* Index allocation can fail on heavy load of commands. This is a temporary
+		 * situation as the current command already holds the semaphore, meaning that
+		 * another command completion is being handled and it is expected to release
+		 * the entry index soon.
+		 */
+		cpu_relax();
+		goto retry;
+	}
+	return idx;
+}
+
 static void cmd_work_handler(struct work_struct *work)
 {
 	struct mlx5_cmd_work_ent *ent = container_of(work, struct mlx5_cmd_work_ent, work);
@@ -900,7 +919,7 @@ static void cmd_work_handler(struct work_struct *work)
 	sem = ent->page_queue ? &cmd->pages_sem : &cmd->sem;
 	down(sem);
 	if (!ent->page_queue) {
-		alloc_ret = cmd_alloc_index(cmd);
+		alloc_ret = cmd_alloc_index_retry(cmd);
 		if (alloc_ret < 0) {
 			mlx5_core_err_rl(dev, "failed to allocate command entry\n");
 			if (ent->callback) {
-- 
2.25.1