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Message-ID: <CAPhsuW61yzkH5Tp0ku37DBjnQzT81yJUx0F4bag4xdq1rX5gsA@mail.gmail.com> Date: Mon, 18 Dec 2023 08:04:50 -0800 From: Song Liu <song@...nel.org> To: Yu Kuai <yukuai1@...weicloud.com> Cc: linan666@...weicloud.com, axboe@...nel.dk, linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com> Subject: Re: [PATCH v2 1/2] md: Fix overflow in is_mddev_idle On Sun, Dec 17, 2023 at 5:39 PM Yu Kuai <yukuai1@...weicloud.com> 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
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