Subject: Re: [PATCH v2] net/mlx5: don't printk garbage when transceiver overheats

From: Leon Romanovsky <[email-masked]>
Date: Thu, 14 May 2026 14:32:57 +0300

On Tue, May 12, 2026 at 12:32:38AM -0700, Will Mortensen wrote:
> When the mlx5 driver processes a temperature warning event, in events.c
> and hwmon.c, temp_warn() calls print_sensor_names_in_bit_set(), which
> calls hwmon_get_sensor_name() to get the NUL-terminated name of the
> relevant sensor, and then prints it to dmesg. In particular,
> print_sensor_names_in_bit_set() passes the bit index ("sensor index")
> within the 128-bit vector in the warning event to
> hwmon_get_sensor_name(). But hwmon_get_sensor_name() was expecting the
> index of the hwmon channel, and the driver registers hwmon channels for
> at most only two sensors: the ASIC sensor (sensor index 0) and the
> module sensor (sensor index 64 or 65 if we're on a 2-port NIC). So when
> the warning event concerned a module, hwmon_get_sensor_name() took the
> 64th or 65th element of the likely 2-element temp_channel_desc array and
> thus returned a pointer to some other kernel memory past the end of it,
> which was printed to dmesg up to the first NUL byte.
> 
> A further difficulty is that, at least in testing on our CX-8 C8240 with
> firmware 40.47.1088, the warning event can have bits set for other
> modules, e.g. if this PCI physical function is associated with
> port/module 0, we might expect bit 64 to be set, but bit 65 (for port/
> module 1) can also be set.
> 
> Fix this by clarifying that the argument to hwmon_get_sensor_name() is
> the raw sensor index, and correctly converting it to the hwmon channel
> index. Return NULL if the sensor index doesn't correspond to a hwmon
> channel (e.g. because it's for the other port's module).
> 
> Fixes: 46fd50cfcc12 ("net/mlx5: Add sensor name to temperature event message")
> Signed-off-by: Will Mortensen <[email-masked]>

Your Signed-off-by needs to be last.

> Reviewed-by: Jeremy Royal <[email-masked]>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/events.c |  2 ++
>  drivers/net/ethernet/mellanox/mlx5/core/hwmon.c  | 15 ++++++++++++++-
>  drivers/net/ethernet/mellanox/mlx5/core/hwmon.h  |  2 +-
>  3 files changed, 17 insertions(+), 2 deletions(-)

I would take a simpler approach by removing this extra complexity and  
using a static temp_channel_desc[64] array, avoiding any dynamic  
allocation. But this change is acceptable as well.

Thanks