Where to look for possible deadlock causes?

We've been having several problems the past days in our production environment, and some of them seem to boil down to database issues.

Just realized we are having deadlocks (68 actually), on database "waypoint":

Can anyone please provide hints on where / how to search for possible deadlock causes?

select version();=> PostgreSQL 9.4.5 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, 64-bit

Found this evidence in log:

2016-03-06 06:58:39 UTC [11807-1] waypointtx@waypoint ERROR:  deadlock detected2016-03-06 06:58:39 UTC [11807-2] waypointtx@waypoint DETAIL:  Process 11807 waits for ShareLock on transaction 370917997; blocked by process 11788.    Process 11788 waits for ShareLock on transaction 370917865; blocked by process 11807.    Process 11807: select * from telemetria_data.insert_tabla_instantaneo($1,$2,$3,$4,$5,$6 ) as result    Process 11788: select * from telemetria_data.insert_tabla_instantaneo($1,$2,$3,$4,$5,$6 ) as result2016-03-06 06:58:39 UTC [11807-3] waypointtx@waypoint HINT:  See server log for query details.2016-03-06 06:58:39 UTC [11807-4] waypointtx@waypoint CONTEXT:  while updating tuple (2836,88) in relation "instantaneo"    SQL statement "UPDATE telemetria_data.instantaneo SET utc = '2016-03-06 06:58:34', registro=now(), power=0, voltaje = 0, valor ='{2147}'::double precision [] WHERE imei=354676055362536 and clase=40;"    PL/pgSQL function telemetria_data.insert_tabla_instantaneo(bigint,timestamp without time zone,integer,double precision[],integer,double precision) line 13 at EXECUTE statement2016-03-06 06:58:39 UTC [11807-5] waypointtx@waypoint STATEMENT:  select * from telemetria_data.insert_tabla_instantaneo($1,$2,$3,$4,$5,$6 ) as result

So it seems that the following part is the problem:

UPDATE telemetria_data.instantaneo ....... WHERE imei=354676055362536 and clase=40;

Am I right?

Possible offending function:

CREATE OR REPLACE FUNCTION telemetria_data.insert_tabla_instantaneo(    bigint,    timestamp without time zone,    integer,    double precision[],    integer,    double precision)  RETURNS boolean AS$BODY$DECLARE     imei ALIAS FOR $1;    utc ALIAS FOR $2;    clase ALIAS FOR $3;    valor ALIAS FOR $4;    power ALIAS FOR $5;    voltaje ALIAS FOR $6;    num_rows int;BEGIN    EXECUTE 'UPDATE telemetria_data.instantaneo SET utc = ''' || utc || ''', registro=now(), power='|| power ||', voltaje = '|| voltaje ||', valor =''{' || array_to_string(valor,',')  ||'}''::double precision [] WHERE imei='|| imei ||' and clase=' || clase || ';';    GET DIAGNOSTICS num_rows = ROW_COUNT;    IF num_rows > 0 THEN    RETURN TRUE;    ELSE    EXECUTE 'insert into telemetria_data.enabled_units (imei,clase) values ('|| imei ||','|| clase ||');';    EXECUTE 'insert into telemetria_data.instantaneo (imei,utc,clase,valor,registro,power,voltaje) values ('|| imei ||',''' || utc || ''','|| clase ||',''{' || array_to_string(valor,',')  ||'}''::double precision [],now(),'|| power ||','|| voltaje ||');';     RETURN TRUE;    END IF;    EXCEPTION    WHEN UNIQUE_VIOLATION THEN        EXECUTE 'insert into telemetria_data.instantaneo (imei,utc,clase,valor,registro,power,voltaje) values ('|| imei ||',''' || utc || ''','|| clase ||',''{' || array_to_string(valor,',')  ||'}''::double precision [],now(),'|| power ||','|| voltaje ||');';         RETURN TRUE;    WHEN foreign_key_violation THEN        RETURN FALSE;END;$BODY$  LANGUAGE plpgsql VOLATILE  COST 100;

Related table structure:

CREATE TABLE telemetria_data.instantaneo(  imei bigint NOT NULL,  utc timestamp without time zone NOT NULL,  clase integer NOT NULL,  valor double precision[],  registro timestamp without time zone DEFAULT now(),  power integer DEFAULT (-1),  voltaje double precision DEFAULT 0.0,  CONSTRAINT pk_telemetria_data_instantaeo PRIMARY KEY (imei, clase),  CONSTRAINT fk_telemetria_data_clase_id FOREIGN KEY (clase)      REFERENCES telemetria_data.clase (id) MATCH SIMPLE      ON UPDATE CASCADE ON DELETE CASCADE)WITH (  OIDS=FALSE);