On Sun, Dec 17, 2023 at 5:39 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote: > [...] > > > > We only use this for idle or not check, the behavior is OK (I think). > > However, this logic is error prone. > > > > On 64-bit systems, there is a 4-byte hole behind sync_io. I think we can > > just use it for atomic64_t so that we don't have to worry about overflow. > > I'm not sure about this, because other than this ubsan warning, this > overflow doesn't have any impact on functionality to me. Fixing warnings for zero or low cost is always a good idea. It helps boost the signal when UBSAN (and other debug features) detects real issues. > If we care about this 'hole', there are lots of holes in gendisk, and > can be avoiled, for example, moving 'sync_io' near to 'node_id'. The point was not "let's fill the hole", but "we can use atomic64_t without extra memory cost". In general, I don't think we care too much about holes in "struct gendisk". Does this make sense? Thanks, Song
