• Ryusuke Konishi's avatar
    nilfs2: fix lockdep warnings in page operations for btree nodes · e897be17
    Ryusuke Konishi authored
    Patch series "nilfs2 lockdep warning fixes".
    
    The first two are to resolve the lockdep warning issue, and the last one
    is the accompanying cleanup and low priority.
    
    Based on your comment, this series solves the issue by separating inode
    object as needed.  Since I was worried about the impact of the object
    composition changes, I tested the series carefully not to cause
    regressions especially for delicate functions such like disk space
    reclamation and snapshots.
    
    This patch (of 3):
    
    If CONFIG_LOCKDEP is enabled, nilfs2 hits lockdep warnings at
    inode_to_wb() during page/folio operations for btree nodes:
    
      WARNING: CPU: 0 PID: 6575 at include/linux/backing-dev.h:269 inode_to_wb include/linux/backing-dev.h:269 [inline]
      WARNING: CPU: 0 PID: 6575 at include/linux/backing-dev.h:269 folio_account_dirtied mm/page-writeback.c:2460 [inline]
      WARNING: CPU: 0 PID: 6575 at include/linux/backing-dev.h:269 __folio_mark_dirty+0xa7c/0xe30 mm/page-writeback.c:2509
      Modules linked in:
      ...
      RIP: 0010:inode_to_wb include/linux/backing-dev.h:269 [inline]
      RIP: 0010:folio_account_dirtied mm/page-writeback.c:2460 [inline]
      RIP: 0010:__folio_mark_dirty+0xa7c/0xe30 mm/page-writeback.c:2509
      ...
      Call Trace:
        __set_page_dirty include/linux/pagemap.h:834 [inline]
        mark_buffer_dirty+0x4e6/0x650 fs/buffer.c:1145
        nilfs_btree_propagate_p fs/nilfs2/btree.c:1889 [inline]
        nilfs_btree_propagate+0x4ae/0xea0 fs/nilfs2/btree.c:2085
        nilfs_bmap_propagate+0x73/0x170 fs/nilfs2/bmap.c:337
        nilfs_collect_dat_data+0x45/0xd0 fs/nilfs2/segment.c:625
        nilfs_segctor_apply_buffers+0x14a/0x470 fs/nilfs2/segment.c:1009
        nilfs_segctor_scan_file+0x47a/0x700 fs/nilfs2/segment.c:1048
        nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1224 [inline]
        nilfs_segctor_collect fs/nilfs2/segment.c:1494 [inline]
        nilfs_segctor_do_construct+0x14f3/0x6c60 fs/nilfs2/segment.c:2036
        nilfs_segctor_construct+0x7a7/0xb30 fs/nilfs2/segment.c:2372
        nilfs_segctor_thread_construct fs/nilfs2/segment.c:2480 [inline]
        nilfs_segctor_thread+0x3c3/0xf90 fs/nilfs2/segment.c:2563
        kthread+0x405/0x4f0 kernel/kthread.c:327
        ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
    
    This is because nilfs2 uses two page caches for each inode and
    inode->i_mapping never points to one of them, the btree node cache.
    
    This causes inode_to_wb(inode) to refer to a different page cache than
    the caller page/folio operations such like __folio_start_writeback(),
    __folio_end_writeback(), or __folio_mark_dirty() acquired the lock.
    
    This patch resolves the issue by allocating and using an additional
    inode to hold the page cache of btree nodes.  The inode is attached
    one-to-one to the traditional nilfs2 inode if it requires a block
    mapping with b-tree.  This setup change is in memory only and does not
    affect the disk format.
    
    Link: https://lkml.kernel.org/r/1647867427-30498-1-git-send-email-konishi.ryusuke@gmail.com
    Link: https://lkml.kernel.org/r/1647867427-30498-2-git-send-email-konishi.ryusuke@gmail.com
    Link: https://lore.kernel.org/r/YXrYvIo8YRnAOJCj@casper.infradead.org
    Link: https://lore.kernel.org/r/9a20b33d-b38f-b4a2-4742-c1eb5b8e4d6c@redhat.comSigned-off-by: default avatarRyusuke Konishi <konishi.ryusuke@gmail.com>
    Reported-by: syzbot+0d5b462a6f07447991b3@syzkaller.appspotmail.com
    Reported-by: syzbot+34ef28bb2aeb28724aa0@syzkaller.appspotmail.com
    Reported-by: default avatarHao Sun <sunhao.th@gmail.com>
    Reported-by: default avatarDavid Hildenbrand <david@redhat.com>
    Tested-by: default avatarRyusuke Konishi <konishi.ryusuke@gmail.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    e897be17
btnode.c 6.99 KB