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

kernel test robot
2021-10-20T02:23:24Z

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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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