[LU-11827] Race between llog_cat_declare_add_rec and llog_cat_current_log

Duplicate — Mon, 1 Apr 2019 14:16:11 +0000

llog_cat_declare_add_rec() operates on &cathandle->u.chd.chd_next_log without having it protected:

int llog_cat_declare_add_rec(const struct lu_env *env,
...
        rc = llog_cat_prep_log(env, cathandle,
                               &cathandle->u.chd.chd_current_log, th);
...
	rc = llog_cat_prep_log(env, cathandle, &cathandle->u.chd.chd_next_log,
                               th);

That races with llog_cat_current_log() when it switches to next log and updates cathandle->u.chd.chd_next_log:

static struct llog_handle *llog_cat_current_log(struct llog_handle *cathandle,
...
        down_write_nested(&cathandle->lgh_lock, LLOGH_CAT);
...
        CDEBUG(D_INODE, "use next log\n");
 
        loghandle = cathandle->u.chd.chd_next_log;
        cathandle->u.chd.chd_current_log = loghandle;
        cathandle->u.chd.chd_next_log = NULL;
        down_write_nested(&loghandle->lgh_lock, LLOGH_LOG);
...

The following trace has been observed:
Process 177713 enters llog_cat_declare_add_rec():

00000040:00000001:19.0:1545138333.143874:0:177713:0:(llog_cat.c:605:llog_cat_declare_add_rec()) Process entered
00000040:00000001:19.0:1545138333.143875:0:177713:0:(llog.c:940:llog_exist()) Process leaving (rc=1 : 1 : 1)
00000040:00000001:19.0:1545138333.143876:0:177713:0:(llog.c:940:llog_exist()) Process leaving (rc=0 : 0 : 0)

Process 99986 jumps in and switches pointer to next log in cathalog handle to NULL:

00000040:00000002:21.0:1545138333.143876:0:99986:0:(llog_cat.c:521:llog_cat_current_log()) use next log

Process 177713 continues: llog_cat_prep_log->llog_declare_create->llog_handle2ops, find NULL in and fails in llog_handle2ops() with -22 as long as *ploghandle is NULL:

00000040:00000001:19.0:1545138333.143877:0:177713:0:(llog.c:954:llog_declare_create()) Process leaving (rc=18446744073709551594 : -22 : ffffffffffffffea)

Whamcloud Community JIRA

[LU-11827] Race between llog_cat_declare_add_rec and llog_cat_current_log