Mysql order by index problem

SELECT
    umb.m AS id,
    umb.s AS STATUS,
    pm.c AS ct,
    pm.v AS vt,
    pm.u AS ut,
    pm.a AS attribute 
FROM
    u umb,
    p pm 
WHERE
    pm.id = umb.m
    AND umb.u = "****" 
    AND ( pm.p = 0 OR pm.p = 1 ) 
ORDER BY
    pm.c DESC
    

two tables are used here: U and p
explain, the result is:
p table is a full table query, extra is Using where; Using filesort
Please tell me how to optimize the query speed, if it is indexing, how to add it, thank you-sharp-sharp-sharp problem description

Sep.21,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b36931-2c03a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36931-2c03a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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