linux-kernel - [peterz-queue:sched/core 13/19] kernel/sched/debug.c:453 print_cfs_group_stats() warn: variable dereferenced before check 'se' (see line 444)

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Date:   Mon, 13 Sep 2021 11:47:51 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Yafang Shao <laoar.shao@...il.com>
Cc:     lkp@...el.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: [peterz-queue:sched/core 13/19] kernel/sched/debug.c:453
 print_cfs_group_stats() warn: variable dereferenced before check 'se' (see
 line 444)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/core
head:   2dfdb3d20ad50e2ae2cb84cbceb0f0fc75e79e5d
commit: 445d9e8ba05d5e9e4b26956b7fe529223e29d8d1 [13/19] sched: make struct sched_statistics independent of fair sched class
config: x86_64-randconfig-m001-20210910 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>

smatch warnings:
kernel/sched/debug.c:453 print_cfs_group_stats() warn: variable dereferenced before check 'se' (see line 444)

vim +/se +453 kernel/sched/debug.c

3866e845ed5222 kernel/sched/debug.c Steven Rostedt (Red Hat  2016-02-22  439) 
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  440  #ifdef CONFIG_FAIR_GROUP_SCHED
5091faa449ee0b kernel/sched_debug.c Mike Galbraith           2010-11-30  441  static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group *tg)
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  442  {
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  443  	struct sched_entity *se = tg->se[cpu];
445d9e8ba05d5e kernel/sched/debug.c Yafang Shao              2021-09-05 @444  	struct sched_statistics *stats = __schedstats_from_se(se);
                                                                                                                                      ^^
New unchecked dereference.

ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  445  
97fb7a0a8944bd kernel/sched/debug.c Ingo Molnar              2018-03-03  446  #define P(F)		SEQ_printf(m, "  .%-30s: %lld\n",	#F, (long long)F)
445d9e8ba05d5e kernel/sched/debug.c Yafang Shao              2021-09-05  447  #define P_SCHEDSTAT(F)	SEQ_printf(m, "  .%-30s: %lld\n",	\
445d9e8ba05d5e kernel/sched/debug.c Yafang Shao              2021-09-05  448  		#F, (long long)schedstat_val(stats->F))
97fb7a0a8944bd kernel/sched/debug.c Ingo Molnar              2018-03-03  449  #define PN(F)		SEQ_printf(m, "  .%-30s: %lld.%06ld\n", #F, SPLIT_NS((long long)F))
445d9e8ba05d5e kernel/sched/debug.c Yafang Shao              2021-09-05  450  #define PN_SCHEDSTAT(F)	SEQ_printf(m, "  .%-30s: %lld.%06ld\n", \
445d9e8ba05d5e kernel/sched/debug.c Yafang Shao              2021-09-05  451  		#F, SPLIT_NS((long long)schedstat_val(stats->F)))
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  452  
cd126afe838d7e kernel/sched/debug.c Yuyang Du                2015-07-15 @453  	if (!se)
                                                                                    ^^^
The old code assumed "se" can be NULL.

18bf2805d9b30c kernel/sched/debug.c Ben Segall               2012-10-04  454  		return;
18bf2805d9b30c kernel/sched/debug.c Ben Segall               2012-10-04  455  
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  456  	PN(se->exec_start);
ff9b48c3598732 kernel/sched_debug.c Bharata B Rao            2008-11-10  457  	PN(se->vruntime);

---
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