git: hammer2 - Correct allocator race and related corruption

Matthew Dillon dillon at
Thu Apr 11 20:08:24 PDT 2019

commit 83815ec6515002d007c3800cb9fd83c9451852f7
Author: Matthew Dillon <dillon at>
Date:   Thu Apr 11 19:04:56 2019 -0700

    hammer2 - Correct allocator race and related corruption
    * When allocating fragments (below 16KB), for example 1K directory
      entries, 1K inodes, compressed file blocks that happen to be
      fragments, or end-of-file fragments, the allocator must ensure
      that any partially freed block is set back to fully allocated.
    * In this specific case the allocator was not setting the
      correct bits in the freemap.  The situation never occurs
      on a block boundary (different code is executed which does
      the correct calculation), so the related block will always
      be in a minimally allocated state (either partially allocated
      or fully allocated).
      This means that the corruption can only happen under the specific
      circumstance where a fragment is allocated out of a block that
      the bulkfree code is simultaneously trying to free (marking it
      partially-allocated).  Because the wrong bits are set, the NEXT
      bulkfree pass can also miss the fact that the fragment is
      allocated and finish transitioning the block from partially-
      allocated to fully-free.
      A later allocation then corrupts the block, resulting in CHECK
      errors on the console.
    * Because the bulkfree code always comes in and in ALL SITUATIONS OTHER
      THAN THIS SPECIFIC RACE will re-mark the blocks fully-allocated,
      the corruption can ONLY occur during heavy write activity during
      a bulkfree operation, typically when heavy manipulation of directory
      entries or inodes occurs.
    * Correct the fragmentary bitmap calculation to set the proper

Summary of changes:
 sys/vfs/hammer2/hammer2_bulkfree.c | 36 +++++++++++++++++++++---------------
 sys/vfs/hammer2/hammer2_freemap.c  | 11 +++++++++--
 2 files changed, 30 insertions(+), 17 deletions(-)

DragonFly BSD source repository

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