Re: [PATCH 2/2] ethdev: fix race on ports for telemetry commands

["Robin Jarry" <rjarry@redhat.com>]

David Marchand, Oct 02, 2024 at 21:06:
> On Wed, Oct 2, 2024 at 6:27 PM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
>>
>> On Wed, Oct 02, 2024 at 05:57:08PM +0200, David Marchand wrote:
>> > While invoking telemetry commands (which may happen at any time,
>> > out of control of the application), an application thread may
>> > concurrently add/remove ports.
>> > The telemetry callbacks may then access partially
>> > initialised/uninitialised ethdev data.
>> >
>> > Reuse the ethdev lock that protects port allocation/destruction.
>> >
>> > Fixes: c190daedb9b1 ("ethdev: add telemetry callbacks")
>> > Cc: stable@dpdk.org
>> >
>> > Signed-off-by: David Marchand <david.marchand@redhat.com>
>> > ---
>> >  lib/ethdev/rte_ethdev_telemetry.c | 93 +++++++++++++++++++------------
>> >  1 file changed, 56 insertions(+), 37 deletions(-)
>> >
>> > diff --git a/lib/ethdev/rte_ethdev_telemetry.c b/lib/ethdev/rte_ethdev_telemetry.c
>> > index 8031a58595..7f9c924209 100644
>> > --- a/lib/ethdev/rte_ethdev_telemetry.c
>> > +++ b/lib/ethdev/rte_ethdev_telemetry.c
>> > @@ -6,6 +6,7 @@
>> >  #include <stdlib.h>
>> >
>> >  #include <rte_kvargs.h>
>> > +#include <rte_spinlock.h>
>> >  #include <rte_telemetry.h>
>> >
>> >  #include "rte_ethdev.h"
>> > @@ -1403,43 +1404,61 @@ eth_dev_handle_port_tm_node_caps(const char *cmd __rte_unused,
>> >       return ret;
>> >  }
>> >
>> > +#define ETHDEV_TELEMETRY_HANDLERS \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/list", eth_dev_handle_port_list, \
>> > +             "Returns list of available ethdev ports. Takes no parameters") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/stats", eth_dev_handle_port_stats, \
>> > +             "Returns the common stats for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/xstats", eth_dev_handle_port_xstats, \
>> > +             "Returns the extended stats for a port. Parameters: int port_id,hide_zero=true|false(Optional for indicates hide zero xstats)") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/dump_priv", eth_dev_handle_port_dump_priv, \
>> > +             "Returns dump private information for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/link_status", eth_dev_handle_port_link_status, \
>> > +             "Returns the link status for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/info", eth_dev_handle_port_info, \
>> > +             "Returns the device info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/module_eeprom", eth_dev_handle_port_module_eeprom, \
>> > +             "Returns module EEPROM info with SFF specs. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/macs", eth_dev_handle_port_macs, \
>> > +             "Returns the MAC addresses for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/flow_ctrl", eth_dev_handle_port_flow_ctrl, \
>> > +             "Returns flow ctrl info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/rx_queue", eth_dev_handle_port_rxq, \
>> > +             "Returns Rx queue info for a port. Parameters: int port_id, int queue_id (Optional if only one queue)") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/tx_queue", eth_dev_handle_port_txq, \
>> > +             "Returns Tx queue info for a port. Parameters: int port_id, int queue_id (Optional if only one queue)") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/dcb", eth_dev_handle_port_dcb, \
>> > +             "Returns DCB info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/rss_info", eth_dev_handle_port_rss_info, \
>> > +             "Returns RSS info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/fec", eth_dev_handle_port_fec, \
>> > +             "Returns FEC info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/vlan", eth_dev_handle_port_vlan, \
>> > +             "Returns VLAN info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/tm_capability", eth_dev_handle_port_tm_caps, \
>> > +             "Returns TM Capabilities info for a port. Parameters: int port_id") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/tm_level_capability", eth_dev_handle_port_tm_level_caps, \
>> > +             "Returns TM Level Capabilities info for a port. Parameters: int port_id, int level_id (see tm_capability for the max)") \
>> > +     ETHDEV_TELEMETRY_HANDLER("/ethdev/tm_node_capability", eth_dev_handle_port_tm_node_caps, \
>> > +             "Returns TM Node Capabilities info for a port. Parameters: int port_id, int node_id (see tm_capability for the max)")
>> > +
>> > +#define ETHDEV_TELEMETRY_HANDLER(command, func, usage) \
>> > +static int func ## _locked(const char *cmd __rte_unused, const char *params, \
>> > +     struct rte_tel_data *d) \
>> > +{ \
>> > +     int ret; \
>> > +     rte_spinlock_lock(rte_mcfg_ethdev_get_lock()); \
>> > +     ret = func(cmd, params, d); \
>> > +     rte_spinlock_unlock(rte_mcfg_ethdev_get_lock()); \
>> > +     return ret; \
>> > +}
>> > +ETHDEV_TELEMETRY_HANDLERS
>> > +#undef ETHDEV_TELEMETRY_HANDLER
>> > +
>>
>> Not really a massive fan of such use of macros in the code, since I think
>> it makes things obscure for the casual reader. However, I see why this
>> approach has been taken. I think the macro code needs some documentation
>> explaining why this was done this way.
>
> I can add comments explaining how this is for protecting accesses to port.
>
>>
>> >  RTE_INIT(ethdev_init_telemetry)
>> >  {
>> > -     rte_telemetry_register_cmd("/ethdev/list", eth_dev_handle_port_list,
>> > -                     "Returns list of available ethdev ports. Takes no parameters");
>> > -     rte_telemetry_register_cmd("/ethdev/stats", eth_dev_handle_port_stats,
>> > -                     "Returns the common stats for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/xstats", eth_dev_handle_port_xstats,
>> > -                     "Returns the extended stats for a port. Parameters: int port_id,hide_zero=true|false(Optional for indicates hide zero xstats)");
>> > -     rte_telemetry_register_cmd("/ethdev/dump_priv", eth_dev_handle_port_dump_priv,
>> > -                     "Returns dump private information for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/link_status",
>> > -                     eth_dev_handle_port_link_status,
>> > -                     "Returns the link status for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/info", eth_dev_handle_port_info,
>> > -                     "Returns the device info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/module_eeprom", eth_dev_handle_port_module_eeprom,
>> > -                     "Returns module EEPROM info with SFF specs. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/macs", eth_dev_handle_port_macs,
>> > -                     "Returns the MAC addresses for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/flow_ctrl", eth_dev_handle_port_flow_ctrl,
>> > -                     "Returns flow ctrl info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/rx_queue", eth_dev_handle_port_rxq,
>> > -                     "Returns Rx queue info for a port. Parameters: int port_id, int queue_id (Optional if only one queue)");
>> > -     rte_telemetry_register_cmd("/ethdev/tx_queue", eth_dev_handle_port_txq,
>> > -                     "Returns Tx queue info for a port. Parameters: int port_id, int queue_id (Optional if only one queue)");
>> > -     rte_telemetry_register_cmd("/ethdev/dcb", eth_dev_handle_port_dcb,
>> > -                     "Returns DCB info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/rss_info", eth_dev_handle_port_rss_info,
>> > -                     "Returns RSS info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/fec", eth_dev_handle_port_fec,
>> > -                     "Returns FEC info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/vlan", eth_dev_handle_port_vlan,
>> > -                     "Returns VLAN info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/tm_capability", eth_dev_handle_port_tm_caps,
>> > -                     "Returns TM Capabilities info for a port. Parameters: int port_id");
>> > -     rte_telemetry_register_cmd("/ethdev/tm_level_capability", eth_dev_handle_port_tm_level_caps,
>> > -                     "Returns TM Level Capabilities info for a port. Parameters: int port_id, int level_id (see tm_capability for the max)");
>> > -     rte_telemetry_register_cmd("/ethdev/tm_node_capability", eth_dev_handle_port_tm_node_caps,
>> > -                     "Returns TM Node Capabilities info for a port. Parameters: int port_id, int node_id (see tm_capability for the max)");
>> > +#define ETHDEV_TELEMETRY_HANDLER(command, func, usage) \
>> > +     rte_telemetry_register_cmd(command, func ## _locked, usage);
>> > +     ETHDEV_TELEMETRY_HANDLERS
>> > +#undef ETHDEV_TELEMETRY_HANDLER
>> >  }
>>
>> An alternative to this macro-fu, is to just define a single ethdev
>> telemetry function, and within that, take the lock and then dispatch to the
>> appropriate subfunction based upon the actual command coming in. The
>> dispatch may be slightly slower due to the additional text matching (only
>> from byte 8 onwards, so very short strings), but I think the code could be
>> a simpler in C rather than in macros, and the perf impact for telemetry is
>> likely to be negligible, compared to the overhead of the socket I/O etc.
>
> Hopefully, dispatching performance is not important here.

I was going to suggest adding a rte_spinlock_t* parameter to a new 
telemetry register function that would need to be held while the 
callback is invoked. Or if we want to keep doors open to other kinds of 
lock, a wrapper callback.

Thoughts?