net/mlx5: Add retry mechanism to the command entry index allocation

commit 410bd754cd73c4a2ac3856d9a03d7b08f9c906bf upstream.

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@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Cc: Timo Rothenpieler <timo@rothenpieler.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/cmd.c b/drivers/net/ethernet/mellanox/mlx5/core/cmd.c
index b00e72b86863a2b80682c33894fb9b590bdb9429..76547d35cd0e1836a6d2ed808bff0f65b2f6b1ba 100644 (file)
--- 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(dev, "failed to allocate command entry\n");
                        if (ent->callback) {