On Mon, Jan 12, 2026 at 04:23:51PM +0100, Fiona Ebner wrote: > Some Proxmox users reported an occasional assertion failure [0][1] in > busy VMs when using drive mirror with active mode. In particular, the > failure may occur for zero writes shorter than the job granularity: > > > #0 0x00007b421154b507 in abort () > > #1 0x00007b421154b420 in ?? () > > #2 0x0000641c582e061f in bitmap_set (map=0x7b4204014e00, start=14, nr=-1) > > #3 0x0000641c58062824 in do_sync_target_write (job=0x641c7e73d1e0, > > method=MIRROR_METHOD_ZERO, offset=852480, bytes=4096, qiov=0x0, > > flags=0) > > #4 0x0000641c58062250 in bdrv_mirror_top_do_write (bs=0x641c7e62e1f0, > method=MIRROR_METHOD_ZERO, copy_to_target=true, offset=852480, > bytes=4096, qiov=0x0, flags=0) > > #5 0x0000641c58061f31 in bdrv_mirror_top_pwrite_zeroes (bs=0x641c7e62e1f0, > offset=852480, bytes=4096, flags=0) > > The range for the dirty bitmap described by dirty_bitmap_offset and > dirty_bitmap_end is narrower than the original range and in fact, > dirty_bitmap_end might be smaller than dirty_bitmap_offset. There > already is a check for 'dirty_bitmap_offset < dirty_bitmap_end' before > resetting the dirty bitmap. Add such a check for setting the zero > bitmap too, which uses the same narrower range. > > [0]: https://forum.proxmox.com/threads/177981/ > [1]: https://bugzilla.proxmox.com/show_bug.cgi?id=7222 > > Cc: [email protected] > Fixes: 7e277545b9 ("mirror: Skip writing zeroes when target is already zero") > Signed-off-by: Fiona Ebner <[email protected]> > --- > block/mirror.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/block/mirror.c b/block/mirror.c > index b344182c74..bc982cb99a 100644 > --- a/block/mirror.c > +++ b/block/mirror.c > @@ -1514,9 +1514,12 @@ do_sync_target_write(MirrorBlockJob *job, MirrorMethod > method, > assert(!qiov); > ret = blk_co_pwrite_zeroes(job->target, offset, bytes, flags); > if (job->zero_bitmap && ret >= 0) { > - bitmap_set(job->zero_bitmap, dirty_bitmap_offset / > job->granularity, > - (dirty_bitmap_end - dirty_bitmap_offset) / > - job->granularity); > + if (dirty_bitmap_offset < dirty_bitmap_end) { > + bitmap_set(job->zero_bitmap, > + dirty_bitmap_offset / job->granularity, > + (dirty_bitmap_end - dirty_bitmap_offset) / > + job->granularity); > + }
Why does this case clause use dirty_bitmap_offset and dirty_bitmap_end
instead of zero_bitmap_offset and zero_bitmap_end like the other
zero_bitmap operations in this switch statement?
if (job->zero_bitmap && ret >= 0) {
- bitmap_set(job->zero_bitmap, dirty_bitmap_offset / job->granularity,
- (dirty_bitmap_end - dirty_bitmap_offset) /
- job->granularity);
+ bitmap_set(job->zero_bitmap, zero_bitmap_offset,
+ zero_bitmap_end - zero_bitmap_offset);
}
I'm probably missing something, but it's not obvious to me :).
Stefan
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