linux-kernel - Re: [PATCH] cgroup/rstat: change cgroup_base

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] [day] [month] [year] [list]

Message-ID: <4rj2fju2cerlxarbqjmd4222jqeoqtltz57uo3ztw6nhirbotk@66brhfp3t5dc>
Date: Wed, 18 Jun 2025 10:21:24 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Bertrand Wlodarczyk <bertrand.wlodarczyk@...el.com>
Cc: tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup/rstat: change cgroup_base_stat to atomic

On Tue, Jun 17, 2025 at 12:26:45PM +0200, Bertrand Wlodarczyk wrote:
> The kernel currently faces scalability issues when multiple userspace
> programs attempt to read cgroup statistics concurrently.
> 
> The primary bottleneck is the css_cgroup_lock in cgroup_rstat_flush,
> which prevents access and updates to the statistics
> of the css from multiple CPUs in parallel.
> 
> Given that rstat operates on a per-CPU basis and only aggregates
> statistics in the parent cgroup, there is no compelling reason
> why these statistics cannot be atomic.
> By eliminating the lock, each CPU can traverse its rstat hierarchy
> independently, without blocking. Synchronization is achieved during
> parent propagation through atomic operations.
> 
> This change significantly enhances performance in scenarios
> where multiple CPUs access CPU rstat within a single cgroup hierarchy,
> yielding a performance improvement of around 50 times compared
> to the mainline version.
> Notably, performance for memory and I/O rstats remains unchanged,
> as these are managed in separate submodules.
> 
> Additionally, this patch addresses a race condition detectable
> in the current mainline by KCSAN in __cgroup_account_cputime,
> which occurs when attempting to read a single hierarchy
> from multiple CPUs.
> 
> Signed-off-by: Bertrand Wlodarczyk <bertrand.wlodarczyk@...el.com>

Can you please rebase your change over for-6.17 branch of the cgroup
tree and resend?