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Date:   Thu, 11 Nov 2021 18:03:22 +0800
From:   kernel test robot <yujie.liu@...el.com>
To:     brookxu <brookxu.cn@...il.com>
CC:     <llvm@...ts.linux.dev>, <kbuild-all@...ts.01.org>,
        <linux-ext4@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: fix a possible ABBA deadlock dued to busy PA

Hi Chunguang,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tytso-ext4/dev]
[also build test WARNING on v5.15 next-20211109]
[cannot apply to tytso-fscrypt/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/brookxu/ext4-fix-a-possible-ABBA-deadlock-dued-to-busy-PA/20210929-091410
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev
config: i386-randconfig-c001-20210929 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project dc6e8dfdfe7efecfda318d43a06fae18b40eb498)
reproduce (this is a W=1 build):
         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
         chmod +x ~/bin/make.cross
         # https://github.com/0day-ci/linux/commit/5e956ecab47126f1d065a1ac6e6d5077e02e6f87
         git remote add linux-review https://github.com/0day-ci/linux
         git fetch --no-tags linux-review brookxu/ext4-fix-a-possible-ABBA-deadlock-dued-to-busy-PA/20210929-091410
         git checkout 5e956ecab47126f1d065a1ac6e6d5077e02e6f87
         # save the attached .config to linux build tree
         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=i386 clang-analyzer

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


clang-analyzer warnings: (new ones prefixed by >>)

 >> fs/ext4/mballoc.c:4849:3: warning: Value stored to 'needed' is never read [clang-analyzer-deadcode.DeadStores]
                    needed = EXT4_CLUSTERS_PER_GROUP(sb) + 1;
                    ^

vim +/needed +4849 fs/ext4/mballoc.c

c9de560ded61faa Alex Tomas            2008-01-29  4805
c9de560ded61faa Alex Tomas            2008-01-29  4806  /*
c9de560ded61faa Alex Tomas            2008-01-29  4807   * releases all preallocations in given group
c9de560ded61faa Alex Tomas            2008-01-29  4808   *
c9de560ded61faa Alex Tomas            2008-01-29  4809   * first, we need to decide discard policy:
c9de560ded61faa Alex Tomas            2008-01-29  4810   * - when do we discard
c9de560ded61faa Alex Tomas            2008-01-29  4811   *   1) ENOSPC
c9de560ded61faa Alex Tomas            2008-01-29  4812   * - how many do we discard
c9de560ded61faa Alex Tomas            2008-01-29  4813   *   1) how many requested
c9de560ded61faa Alex Tomas            2008-01-29  4814   */
4ddfef7b41aebbb Eric Sandeen          2008-04-29  4815  static noinline_for_stack int
4ddfef7b41aebbb Eric Sandeen          2008-04-29  4816  ext4_mb_discard_group_preallocations(struct super_block *sb,
5e956ecab47126f Chunguang Xu          2021-09-29  4817  				     ext4_group_t group, int needed, int *busy)
c9de560ded61faa Alex Tomas            2008-01-29  4818  {
c9de560ded61faa Alex Tomas            2008-01-29  4819  	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
c9de560ded61faa Alex Tomas            2008-01-29  4820  	struct buffer_head *bitmap_bh = NULL;
c9de560ded61faa Alex Tomas            2008-01-29  4821  	struct ext4_prealloc_space *pa, *tmp;
c9de560ded61faa Alex Tomas            2008-01-29  4822  	struct list_head list;
c9de560ded61faa Alex Tomas            2008-01-29  4823  	struct ext4_buddy e4b;
c9de560ded61faa Alex Tomas            2008-01-29  4824  	int err;
5e956ecab47126f Chunguang Xu          2021-09-29  4825  	int free = 0;
c9de560ded61faa Alex Tomas            2008-01-29  4826
d3df14535f4a5b5 Ritesh Harjani        2020-05-10  4827  	mb_debug(sb, "discard preallocation for group %u\n", group);
c9de560ded61faa Alex Tomas            2008-01-29  4828  	if (list_empty(&grp->bb_prealloc_list))
bbc4ec77e9f9c7a Ritesh Harjani        2020-05-10  4829  		goto out_dbg;
c9de560ded61faa Alex Tomas            2008-01-29  4830
574ca174c97f790 Theodore Ts'o         2008-07-11  4831  	bitmap_bh = ext4_read_block_bitmap(sb, group);
9008a58e5dcee01 Darrick J. Wong       2015-10-17  4832  	if (IS_ERR(bitmap_bh)) {
9008a58e5dcee01 Darrick J. Wong       2015-10-17  4833  		err = PTR_ERR(bitmap_bh);
54d3adbc29f0c7c Theodore Ts'o         2020-03-28  4834  		ext4_error_err(sb, -err,
54d3adbc29f0c7c Theodore Ts'o         2020-03-28  4835  			       "Error %d reading block bitmap for %u",
9008a58e5dcee01 Darrick J. Wong       2015-10-17  4836  			       err, group);
bbc4ec77e9f9c7a Ritesh Harjani        2020-05-10  4837  		goto out_dbg;
c9de560ded61faa Alex Tomas            2008-01-29  4838  	}
c9de560ded61faa Alex Tomas            2008-01-29  4839
c9de560ded61faa Alex Tomas            2008-01-29  4840  	err = ext4_mb_load_buddy(sb, group, &e4b);
ce89f46cb833f89 Aneesh Kumar K.V      2008-07-23  4841  	if (err) {
9651e6b2e20648d Konstantin Khlebnikov 2017-05-21  4842  		ext4_warning(sb, "Error %d loading buddy information for %u",
9651e6b2e20648d Konstantin Khlebnikov 2017-05-21  4843  			     err, group);
ce89f46cb833f89 Aneesh Kumar K.V      2008-07-23  4844  		put_bh(bitmap_bh);
bbc4ec77e9f9c7a Ritesh Harjani        2020-05-10  4845  		goto out_dbg;
ce89f46cb833f89 Aneesh Kumar K.V      2008-07-23  4846  	}
c9de560ded61faa Alex Tomas            2008-01-29  4847
c9de560ded61faa Alex Tomas            2008-01-29  4848  	if (needed == 0)
7137d7a48e2213e Theodore Ts'o         2011-09-09 @4849  		needed = EXT4_CLUSTERS_PER_GROUP(sb) + 1;
c9de560ded61faa Alex Tomas            2008-01-29  4850
c9de560ded61faa Alex Tomas            2008-01-29  4851  	INIT_LIST_HEAD(&list);
c9de560ded61faa Alex Tomas            2008-01-29  4852  	ext4_lock_group(sb, group);
c9de560ded61faa Alex Tomas            2008-01-29  4853  	list_for_each_entry_safe(pa, tmp,
c9de560ded61faa Alex Tomas            2008-01-29  4854  				&grp->bb_prealloc_list, pa_group_list) {
c9de560ded61faa Alex Tomas            2008-01-29  4855  		spin_lock(&pa->pa_lock);
c9de560ded61faa Alex Tomas            2008-01-29  4856  		if (atomic_read(&pa->pa_count)) {
c9de560ded61faa Alex Tomas            2008-01-29  4857  			spin_unlock(&pa->pa_lock);
5e956ecab47126f Chunguang Xu          2021-09-29  4858  			*busy = 1;
c9de560ded61faa Alex Tomas            2008-01-29  4859  			continue;
c9de560ded61faa Alex Tomas            2008-01-29  4860  		}
c9de560ded61faa Alex Tomas            2008-01-29  4861  		if (pa->pa_deleted) {
c9de560ded61faa Alex Tomas            2008-01-29  4862  			spin_unlock(&pa->pa_lock);
c9de560ded61faa Alex Tomas            2008-01-29  4863  			continue;
c9de560ded61faa Alex Tomas            2008-01-29  4864  		}
c9de560ded61faa Alex Tomas            2008-01-29  4865
c9de560ded61faa Alex Tomas            2008-01-29  4866  		/* seems this one can be freed ... */
27bc446e2def38d brookxu               2020-08-17  4867  		ext4_mb_mark_pa_deleted(sb, pa);
c9de560ded61faa Alex Tomas            2008-01-29  4868
70022da804f0f3f Ye Bin                2020-09-16  4869  		if (!free)
70022da804f0f3f Ye Bin                2020-09-16  4870  			this_cpu_inc(discard_pa_seq);
70022da804f0f3f Ye Bin                2020-09-16  4871
c9de560ded61faa Alex Tomas            2008-01-29  4872  		/* we can trust pa_free ... */
c9de560ded61faa Alex Tomas            2008-01-29  4873  		free += pa->pa_free;
c9de560ded61faa Alex Tomas            2008-01-29  4874
c9de560ded61faa Alex Tomas            2008-01-29  4875  		spin_unlock(&pa->pa_lock);
c9de560ded61faa Alex Tomas            2008-01-29  4876
c9de560ded61faa Alex Tomas            2008-01-29  4877  		list_del(&pa->pa_group_list);
c9de560ded61faa Alex Tomas            2008-01-29  4878  		list_add(&pa->u.pa_tmp_list, &list);
c9de560ded61faa Alex Tomas            2008-01-29  4879  	}
c9de560ded61faa Alex Tomas            2008-01-29  4880
c9de560ded61faa Alex Tomas            2008-01-29  4881  	/* now free all selected PAs */
c9de560ded61faa Alex Tomas            2008-01-29  4882  	list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {
c9de560ded61faa Alex Tomas            2008-01-29  4883
c9de560ded61faa Alex Tomas            2008-01-29  4884  		/* remove from object (inode or locality group) */
c9de560ded61faa Alex Tomas            2008-01-29  4885  		spin_lock(pa->pa_obj_lock);
c9de560ded61faa Alex Tomas            2008-01-29  4886  		list_del_rcu(&pa->pa_inode_list);
c9de560ded61faa Alex Tomas            2008-01-29  4887  		spin_unlock(pa->pa_obj_lock);
c9de560ded61faa Alex Tomas            2008-01-29  4888
cc0fb9ad7dbc5a1 Aneesh Kumar K.V      2009-03-27  4889  		if (pa->pa_type == MB_GROUP_PA)
3e1e5f501632460 Eric Sandeen          2010-10-27  4890  			ext4_mb_release_group_pa(&e4b, pa);
c9de560ded61faa Alex Tomas            2008-01-29  4891  		else
3e1e5f501632460 Eric Sandeen          2010-10-27  4892  			ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);
c9de560ded61faa Alex Tomas            2008-01-29  4893
c9de560ded61faa Alex Tomas            2008-01-29  4894  		list_del(&pa->u.pa_tmp_list);
c9de560ded61faa Alex Tomas            2008-01-29  4895  		call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
c9de560ded61faa Alex Tomas            2008-01-29  4896  	}
c9de560ded61faa Alex Tomas            2008-01-29  4897
c9de560ded61faa Alex Tomas            2008-01-29  4898  	ext4_unlock_group(sb, group);
e39e07fdfd98be8 Jing Zhang            2010-05-14  4899  	ext4_mb_unload_buddy(&e4b);
c9de560ded61faa Alex Tomas            2008-01-29  4900  	put_bh(bitmap_bh);
bbc4ec77e9f9c7a Ritesh Harjani        2020-05-10  4901  out_dbg:
d3df14535f4a5b5 Ritesh Harjani        2020-05-10  4902  	mb_debug(sb, "discarded (%d) blocks preallocated for group %u bb_free (%d)\n",
5e956ecab47126f Chunguang Xu          2021-09-29  4903  		 free, group, grp->bb_free);
5e956ecab47126f Chunguang Xu          2021-09-29  4904  	return free;
c9de560ded61faa Alex Tomas            2008-01-29  4905  }
c9de560ded61faa Alex Tomas            2008-01-29  4906

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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