linux-kernel - Re: [PATCH v2] blk-cgroup: Replace u64_sync with blkg_stat

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Zo8HTD2AD-b51q0C@slm.duckdns.org>
Date: Wed, 10 Jul 2024 12:12:28 -1000
From: Tejun Heo <tj@...nel.org>
To: "boy.wu" <boy.wu@...iatek.com>
Cc: Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Boris Burkov <boris@....io>, cgroups@...r.kernel.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, iverlin.wang@...iatek.com
Subject: Re: [PATCH v2] blk-cgroup: Replace u64_sync with blkg_stat_lock for
 stats update

Hello,

On Wed, Jul 10, 2024 at 02:13:34PM +0800, boy.wu wrote:
...
> @@ -952,7 +952,6 @@ static void blkcg_fill_root_iostats(void)
>  		struct blkcg_gq *blkg = bdev->bd_disk->queue->root_blkg;
>  		struct blkg_iostat tmp;
>  		int cpu;
> -		unsigned long flags;
>  
>  		memset(&tmp, 0, sizeof(tmp));
>  		for_each_possible_cpu(cpu) {
> @@ -974,9 +973,10 @@ static void blkcg_fill_root_iostats(void)
>  				cpu_dkstats->sectors[STAT_DISCARD] << 9;
>  		}
>  
> -		flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
> +#if BITS_PER_LONG == 32
> +		guard(raw_spinlock_irqsave)(&blkg_stat_lock);
> +#endif
>  		blkg_iostat_set(&blkg->iostat.cur, &tmp);
> -		u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);

Isn't the problem shared across other blkg->iostat.sync users too? Also,
maybe, we can just grab the spinlock without testing for 32bit. blkg->iostat
(unlike the per-cpu counterpart) isn't accessed that frequently, so keeping
it simple and consistent probably makes more sense, right?

Thanks.

-- 
tejun