linux-kernel - Re: [PATCH v3] scx: Fix raciness in scx_ops

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: <ZxwJovsaUSv8b_Zg@slm.duckdns.org>
Date: Fri, 25 Oct 2024 11:12:02 -1000
From: Tejun Heo <tj@...nel.org>
To: David Vernet <void@...ifault.com>
Cc: sched-ext@...a.com, kernel-team@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] scx: Fix raciness in scx_ops_bypass()

On Fri, Oct 25, 2024 at 03:54:08PM -0500, David Vernet wrote:
> scx_ops_bypass() can currently race on the ops enable / disable path as
> follows:
> 
> 1. scx_ops_bypass(true) called on enable path, bypass depth is set to 1
> 2. An op on the init path exits, which schedules scx_ops_disable_workfn()
> 3. scx_ops_bypass(false) is called on the disable path, and bypass depth
>    is decremented to 0
> 4. kthread is scheduled to execute scx_ops_disable_workfn()
> 5. scx_ops_bypass(true) called, bypass depth set to 1
> 6. scx_ops_bypass() races when iterating over CPUs
> 
> While it's not safe to take any blocking locks on the bypass path, it is
> safe to take a raw spinlock which cannot be preempted. This patch therefore
> updates scx_ops_bypass() to use a raw spinlock to synchronize, and changes
> scx_ops_bypass_depth to be a regular int.
> 
> Without this change, we observe the following warnings when running the
> 'exit' sched_ext selftest (sometimes requires a couple of runs):
...
> Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class")
> Signed-off-by: David Vernet <void@...ifault.com>

Applied to sched_ext/for-6.12-fixes. Thanks!

-- 
tejun