From: Jiayuan Chen <jiayuan.chen@linux.dev>
To: cgroups@vger.kernel.org
Cc: tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com,
linux-kernel@vger.kernel.org,
Jiayuan Chen <jiayuan.chen@linux.dev>
Subject: [PATCH v1] cgroup: drop preemption_disabled checking
Date: Wed, 19 Nov 2025 19:14:01 +0800 [thread overview]
Message-ID: <20251119111402.153727-1-jiayuan.chen@linux.dev> (raw)
BPF programs do not disable preemption, they only disable migration.
Therefore, when running the cgroup_hierarchical_stats selftest, a
warning [1] is generated.
The css_rstat_updated() function is lockless and reentrant, so checking
for disabled preemption is unnecessary (please correct me if I'm wrong).
[1]:
~/tools/testing/selftests/bpf$
test_progs -a cgroup_hierarchical_stats
...
------------[ cut here ]------------
WARNING: CPU: 0 PID: 382 at kernel/cgroup/rstat.c:84
Modules linked in:
RIP: 0010:css_rstat_updated+0x9d/0x160
...
PKRU: 55555554
Call Trace:
<TASK>
bpf_prog_16a1c2d081688506_counter+0x143/0x14e
bpf_trampoline_6442524909+0x4b/0xb7
cgroup_attach_task+0x5/0x330
? __cgroup_procs_write+0x1d7/0x2f0
cgroup_procs_write+0x17/0x30
cgroup_file_write+0xa6/0x2d0
kernfs_fop_write_iter+0x188/0x240
vfs_write+0x2da/0x5a0
ksys_write+0x77/0x100
__x64_sys_write+0x19/0x30
x64_sys_call+0x79/0x26a0
do_syscall_64+0x89/0x790
? irqentry_exit+0x77/0xb0
? __this_cpu_preempt_check+0x13/0x20
? lockdep_hardirqs_on+0xce/0x170
? irqentry_exit_to_user_mode+0xf2/0x290
? irqentry_exit+0x77/0xb0
? clear_bhb_loop+0x50/0xa0
? clear_bhb_loop+0x50/0xa0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
---[ end trace 0000000000000000 ]---
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
kernel/cgroup/rstat.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index a198e40c799b..fe0d22280cbd 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -81,8 +81,6 @@ __bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu)
if (!css_uses_rstat(css))
return;
- lockdep_assert_preemption_disabled();
-
/*
* For archs withnot nmi safe cmpxchg or percpu ops support, ignore
* the requests from nmi context.
--
2.43.0
next reply other threads:[~2025-11-19 11:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-19 11:14 Jiayuan Chen [this message]
2025-11-19 15:59 ` [PATCH v1] cgroup: drop preemption_disabled checking Tejun Heo
2025-11-20 1:57 ` Jiayuan Chen
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