linux-ext4 - Re: [PATCH 5/5] ext4: Use buckets for cr 1 block scan instead of rbtree

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Date:   Thu, 8 Sep 2022 14:00:17 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...ts.01.org, Jan Kara <jack@...e.cz>,
        Ted Tso <tytso@....edu>
Cc:     lkp@...el.com, kbuild-all@...ts.01.org, linux-ext4@...r.kernel.org,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Ojaswin Mujoo <ojaswin@...ux.ibm.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 5/5] ext4: Use buckets for cr 1 block scan instead of
 rbtree

Hi Jan,

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Jan-Kara/ext4-Fix-performance-regression-with-mballoc/20220907-000945
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 53e99dcff61e1523ec1c3628b2d564ba15d32eb7
config: m68k-randconfig-m041-20220906 (https://download.01.org/0day-ci/archive/20220907/202209071206.u1iHKVzB-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 12.1.0

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

New smatch warnings:
fs/ext4/mballoc.c:945 ext4_mb_choose_next_group_cr1() error: uninitialized symbol 'grp'.

vim +/grp +945 fs/ext4/mballoc.c

196e402adf2e4c Harshad Shirwadkar 2021-04-01  909  static void ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
196e402adf2e4c Harshad Shirwadkar 2021-04-01  910  		int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
196e402adf2e4c Harshad Shirwadkar 2021-04-01  911  {
196e402adf2e4c Harshad Shirwadkar 2021-04-01  912  	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
31b571b608cf66 Jan Kara           2022-09-06  913  	struct ext4_group_info *grp, *iter;
31b571b608cf66 Jan Kara           2022-09-06  914  	int i;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  915  
196e402adf2e4c Harshad Shirwadkar 2021-04-01  916  	if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
196e402adf2e4c Harshad Shirwadkar 2021-04-01  917  		if (sbi->s_mb_stats)
196e402adf2e4c Harshad Shirwadkar 2021-04-01  918  			atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
31b571b608cf66 Jan Kara           2022-09-06  919  	}
31b571b608cf66 Jan Kara           2022-09-06  920  
31b571b608cf66 Jan Kara           2022-09-06  921  	for (i = mb_avg_fragment_size_order(ac->ac_sb, ac->ac_g_ex.fe_len);
31b571b608cf66 Jan Kara           2022-09-06  922  	     i < MB_NUM_ORDERS(ac->ac_sb); i++) {
31b571b608cf66 Jan Kara           2022-09-06  923  		if (list_empty(&sbi->s_mb_avg_fragment_size[i]))
31b571b608cf66 Jan Kara           2022-09-06  924  			continue;
31b571b608cf66 Jan Kara           2022-09-06  925  		read_lock(&sbi->s_mb_avg_fragment_size_locks[i]);
31b571b608cf66 Jan Kara           2022-09-06  926  		if (list_empty(&sbi->s_mb_avg_fragment_size[i])) {
31b571b608cf66 Jan Kara           2022-09-06  927  			read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
31b571b608cf66 Jan Kara           2022-09-06  928  			continue;

Smatch worries that we can hit these two continues on every iteration.
Why not just initialize "grp = NULL;" at the start of the function?

31b571b608cf66 Jan Kara           2022-09-06  929  		}
31b571b608cf66 Jan Kara           2022-09-06  930  		grp = NULL;
31b571b608cf66 Jan Kara           2022-09-06  931  		list_for_each_entry(iter, &sbi->s_mb_avg_fragment_size[i],
31b571b608cf66 Jan Kara           2022-09-06  932  				    bb_avg_fragment_size_node) {
196e402adf2e4c Harshad Shirwadkar 2021-04-01  933  			if (sbi->s_mb_stats)
196e402adf2e4c Harshad Shirwadkar 2021-04-01  934  				atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
31b571b608cf66 Jan Kara           2022-09-06  935  			if (likely(ext4_mb_good_group(ac, iter->bb_group, 1))) {
31b571b608cf66 Jan Kara           2022-09-06  936  				grp = iter;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  937  				break;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  938  			}
196e402adf2e4c Harshad Shirwadkar 2021-04-01  939  		}
31b571b608cf66 Jan Kara           2022-09-06  940  		read_unlock(&sbi->s_mb_avg_fragment_size_locks[i]);
31b571b608cf66 Jan Kara           2022-09-06  941  		if (grp)
31b571b608cf66 Jan Kara           2022-09-06  942  			break;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  943  	}
196e402adf2e4c Harshad Shirwadkar 2021-04-01  944  
31b571b608cf66 Jan Kara           2022-09-06 @945  	if (grp) {
196e402adf2e4c Harshad Shirwadkar 2021-04-01  946  		*group = grp->bb_group;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  947  		ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  948  	} else {
196e402adf2e4c Harshad Shirwadkar 2021-04-01  949  		*new_cr = 2;
196e402adf2e4c Harshad Shirwadkar 2021-04-01  950  	}
196e402adf2e4c Harshad Shirwadkar 2021-04-01  951  }

-- 
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