Re: [PATCH] btrfs: fix deadlock when defragging transparent huge pages

[kernel test robot <lkp@intel.com>]

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Hi Omar,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kdave/for-next]
[also build test WARNING on next-20211019]
[cannot apply to v5.15-rc6]
[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/Omar-Sandoval/btrfs-fix-deadlock-when-defragging-transparent-huge-pages/20211020-051720
base:   https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git for-next
config: arm64-buildonly-randconfig-r006-20211019 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project b37efed957ed0a0193d80020aefd55cb587dfc1f)
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
        # install arm64 cross compiling tool for clang build
        # apt-get install binutils-aarch64-linux-gnu
        # https://github.com/0day-ci/linux/commit/de2627b93b1f0e1c54aece05172608bb4eff77ac
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Omar-Sandoval/btrfs-fix-deadlock-when-defragging-transparent-huge-pages/20211020-051720
        git checkout de2627b93b1f0e1c54aece05172608bb4eff77ac
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=arm64 

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

All warnings (new ones prefixed by >>):

>> fs/btrfs/ioctl.c:1083:10: warning: incompatible integer to pointer conversion returning 'int' from a function with result type 'struct page *' [-Wint-conversion]
                   return -ETXTBSY;
                          ^~~~~~~~
   1 warning generated.


vim +1083 fs/btrfs/ioctl.c

  1043	
  1044	/*
  1045	 * Prepare one page to be defragged.
  1046	 *
  1047	 * This will ensure:
  1048	 *
  1049	 * - Returned page is locked and has been set up properly.
  1050	 * - No ordered extent exists in the page.
  1051	 * - The page is uptodate.
  1052	 *
  1053	 * NOTE: Caller should also wait for page writeback after the cluster is
  1054	 * prepared, here we don't do writeback wait for each page.
  1055	 */
  1056	static struct page *defrag_prepare_one_page(struct btrfs_inode *inode,
  1057						    pgoff_t index)
  1058	{
  1059		struct address_space *mapping = inode->vfs_inode.i_mapping;
  1060		gfp_t mask = btrfs_alloc_write_mask(mapping);
  1061		u64 page_start = (u64)index << PAGE_SHIFT;
  1062		u64 page_end = page_start + PAGE_SIZE - 1;
  1063		struct extent_state *cached_state = NULL;
  1064		struct page *page;
  1065		int ret;
  1066	
  1067	again:
  1068		page = find_or_create_page(mapping, index, mask);
  1069		if (!page)
  1070			return ERR_PTR(-ENOMEM);
  1071	
  1072		/*
  1073		 * Since we can defragment files opened read-only, we can encounter
  1074		 * transparent huge pages here (see CONFIG_READ_ONLY_THP_FOR_FS). We
  1075		 * can't do I/O using huge pages yet, so return an error for now.
  1076		 * Filesystem transparent huge pages are typically only used for
  1077		 * executables that explicitly enable them, so this isn't very
  1078		 * restrictive.
  1079		 */
  1080		if (PageCompound(page)) {
  1081			unlock_page(page);
  1082			put_page(page);
> 1083			return -ETXTBSY;
  1084		}
  1085	
  1086		ret = set_page_extent_mapped(page);
  1087		if (ret < 0) {
  1088			unlock_page(page);
  1089			put_page(page);
  1090			return ERR_PTR(ret);
  1091		}
  1092	
  1093		/* Wait for any existing ordered extent in the range */
  1094		while (1) {
  1095			struct btrfs_ordered_extent *ordered;
  1096	
  1097			lock_extent_bits(&inode->io_tree, page_start, page_end, &cached_state);
  1098			ordered = btrfs_lookup_ordered_range(inode, page_start, PAGE_SIZE);
  1099			unlock_extent_cached(&inode->io_tree, page_start, page_end,
  1100					     &cached_state);
  1101			if (!ordered)
  1102				break;
  1103	
  1104			unlock_page(page);
  1105			btrfs_start_ordered_extent(ordered, 1);
  1106			btrfs_put_ordered_extent(ordered);
  1107			lock_page(page);
  1108			/*
  1109			 * We unlocked the page above, so we need check if it was
  1110			 * released or not.
  1111			 */
  1112			if (page->mapping != mapping || !PagePrivate(page)) {
  1113				unlock_page(page);
  1114				put_page(page);
  1115				goto again;
  1116			}
  1117		}
  1118	
  1119		/*
  1120		 * Now the page range has no ordered extent any more.  Read the page to
  1121		 * make it uptodate.
  1122		 */
  1123		if (!PageUptodate(page)) {
  1124			btrfs_readpage(NULL, page);
  1125			lock_page(page);
  1126			if (page->mapping != mapping || !PagePrivate(page)) {
  1127				unlock_page(page);
  1128				put_page(page);
  1129				goto again;
  1130			}
  1131			if (!PageUptodate(page)) {
  1132				unlock_page(page);
  1133				put_page(page);
  1134				return ERR_PTR(-EIO);
  1135			}
  1136		}
  1137		return page;
  1138	}
  1139	

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

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