Btrfs: fix deadlock on page lock when doing auto-defragment
When I ran xfstests circularly on a auto-defragment btrfs, the deadlock happened. Steps to reproduce: [tty0] # export MOUNT_OPTIONS="-o autodefrag" # export TEST_DEV=<partition1> # export TEST_DIR=<mountpoint1> # export SCRATCH_DEV=<partition2> # export SCRATCH_MNT=<mountpoint2> # while [ 1 ] > do > ./check 091 127 263 > sleep 1 > done [tty1] # while [ 1 ] > do > echo 3 > /proc/sys/vm/drop_caches > done Several hours later, the test processes will hang on, and the deadlock will happen on page lock. The reason is that: Auto defrag task Flush thread Test task btrfs_writepages() add ordered extent (including page 1, 2) set page 1 writeback set page 2 writeback endio_fn() end page 2 writeback release page 2 lock page 1 alloc and lock page 2 page 2 is not uptodate btrfs_readpage() start ordered extent() btrfs_writepages() try to lock page 1 so deadlock happens. Fix this bug by unlocking the page which is in writeback, and re-locking it after the writeback end. Signed-off-by: Miao Xie <miax@cn.fujitsu.com>
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@ -862,6 +862,7 @@ static int cluster_pages_for_defrag(struct inode *inode,
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int i_done;
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struct btrfs_ordered_extent *ordered;
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struct extent_state *cached_state = NULL;
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struct extent_io_tree *tree;
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gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
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if (isize == 0)
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@ -872,18 +873,34 @@ static int cluster_pages_for_defrag(struct inode *inode,
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num_pages << PAGE_CACHE_SHIFT);
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if (ret)
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return ret;
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again:
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ret = 0;
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i_done = 0;
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tree = &BTRFS_I(inode)->io_tree;
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/* step one, lock all the pages */
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for (i = 0; i < num_pages; i++) {
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struct page *page;
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again:
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page = find_or_create_page(inode->i_mapping,
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start_index + i, mask);
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start_index + i, mask);
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if (!page)
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break;
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page_start = page_offset(page);
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page_end = page_start + PAGE_CACHE_SIZE - 1;
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while (1) {
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lock_extent(tree, page_start, page_end, GFP_NOFS);
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ordered = btrfs_lookup_ordered_extent(inode,
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page_start);
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unlock_extent(tree, page_start, page_end, GFP_NOFS);
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if (!ordered)
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break;
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unlock_page(page);
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btrfs_start_ordered_extent(inode, ordered, 1);
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btrfs_put_ordered_extent(ordered);
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lock_page(page);
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}
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if (!PageUptodate(page)) {
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btrfs_readpage(NULL, page);
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lock_page(page);
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@ -894,15 +911,22 @@ again:
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break;
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}
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}
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isize = i_size_read(inode);
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file_end = (isize - 1) >> PAGE_CACHE_SHIFT;
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if (!isize || page->index > file_end ||
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page->mapping != inode->i_mapping) {
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if (!isize || page->index > file_end) {
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/* whoops, we blew past eof, skip this page */
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unlock_page(page);
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page_cache_release(page);
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break;
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}
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if (page->mapping != inode->i_mapping) {
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unlock_page(page);
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page_cache_release(page);
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goto again;
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}
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pages[i] = page;
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i_done++;
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}
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@ -925,25 +949,6 @@ again:
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lock_extent_bits(&BTRFS_I(inode)->io_tree,
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page_start, page_end - 1, 0, &cached_state,
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GFP_NOFS);
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ordered = btrfs_lookup_first_ordered_extent(inode, page_end - 1);
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if (ordered &&
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ordered->file_offset + ordered->len > page_start &&
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ordered->file_offset < page_end) {
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btrfs_put_ordered_extent(ordered);
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unlock_extent_cached(&BTRFS_I(inode)->io_tree,
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page_start, page_end - 1,
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&cached_state, GFP_NOFS);
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for (i = 0; i < i_done; i++) {
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unlock_page(pages[i]);
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page_cache_release(pages[i]);
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}
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btrfs_wait_ordered_range(inode, page_start,
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page_end - page_start);
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goto again;
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}
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if (ordered)
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btrfs_put_ordered_extent(ordered);
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clear_extent_bit(&BTRFS_I(inode)->io_tree, page_start,
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page_end - 1, EXTENT_DIRTY | EXTENT_DELALLOC |
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EXTENT_DO_ACCOUNTING, 0, 0, &cached_state,
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