block_copy_reset_unallocated may yield, and during this yield someone may handle dirty bits which we are handling. Calling block_copy_with_* functions on non-dirty region will lead to copying updated data, which is wrong.
To be sure, that we call block_copy_with_* functions on dirty region, check dirty bitmap _after_ block_copy_reset_unallocated. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- Hi! Suddenly I understand that there is a bug in [PATCH v13 15/15] block/backup: use backup-top instead of write notifiers (queued at Max's https://git.xanclic.moe/XanClic/qemu/commits/branch/block) And here is a fix, which may be squashed to "block/backup: use backup-top instead of write notifiers" commit. block/block-copy.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-) diff --git a/block/block-copy.c b/block/block-copy.c index 55bc360d22..430b88124f 100644 --- a/block/block-copy.c +++ b/block/block-copy.c @@ -292,7 +292,7 @@ int coroutine_fn block_copy(BlockCopyState *s, assert(QEMU_IS_ALIGNED(end, s->cluster_size)); while (start < end) { - int64_t dirty_end; + int64_t chunk_end = end, dirty_end; if (!bdrv_dirty_bitmap_get(s->copy_bitmap, start)) { trace_block_copy_skip(s, start); @@ -300,12 +300,6 @@ int coroutine_fn block_copy(BlockCopyState *s, continue; /* already copied */ } - dirty_end = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, start, - (end - start)); - if (dirty_end < 0) { - dirty_end = end; - } - if (s->skip_unallocated) { ret = block_copy_reset_unallocated(s, start, &status_bytes); if (ret == 0) { @@ -313,20 +307,37 @@ int coroutine_fn block_copy(BlockCopyState *s, start += status_bytes; continue; } + + if (!bdrv_dirty_bitmap_get(s->copy_bitmap, start)) { + /* + * Someone already handled this bit during yield in + * block_copy_reset_unallocated. + */ + trace_block_copy_skip(s, start); + start += s->cluster_size; + continue; + } + /* Clamp to known allocated region */ - dirty_end = MIN(dirty_end, start + status_bytes); + chunk_end = MIN(chunk_end, start + status_bytes); + } + + dirty_end = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, start, + chunk_end - start); + if (dirty_end >= 0) { + chunk_end = MIN(chunk_end, dirty_end); } trace_block_copy_process(s, start); if (s->use_copy_range) { - ret = block_copy_with_offload(s, start, dirty_end); + ret = block_copy_with_offload(s, start, chunk_end); if (ret < 0) { s->use_copy_range = false; } } if (!s->use_copy_range) { - ret = block_copy_with_bounce_buffer(s, start, dirty_end, + ret = block_copy_with_bounce_buffer(s, start, chunk_end, error_is_read, &bounce_buffer); } if (ret < 0) { -- 2.21.0
