diff options
| author | Cunlong Li <shenxiaogll@gmail.com> | 2026-05-20 11:30:54 +0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-05-20 09:44:35 -1000 |
| commit | 22572dbcd3486e6c4dced877125bbf50e4e24edf (patch) | |
| tree | 31e4b595959b5d9c5ed80776678ceb55658614a9 /kernel/cgroup | |
| parent | 8817005efbdfdf5d4e4814cb5dc52b53d12917d7 (diff) | |
cgroup: rstat: relax NMI guard after switch to try_cmpxchg
Commit 36df6e3dbd7e ("cgroup: make css_rstat_updated nmi safe") used
this_cpu_cmpxchg() for the lockless insertion, and therefore required
both ARCH_HAVE_NMI_SAFE_CMPXCHG and ARCH_HAS_NMI_SAFE_THIS_CPU_OPS in
the NMI guard: on archs without the latter, this_cpu_cmpxchg() falls
back to "local_irq_save() + plain cmpxchg", and local_irq_save()
cannot mask NMIs.
Commit 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in
css_rstat_updated") later replaced this_cpu_cmpxchg() with plain
try_cmpxchg() to fix cross-CPU lockless-list corruption, but left the
NMI guard untouched. After that switch, css_rstat_updated() no longer
performs any this_cpu_*() RMW operations and only relies on the arch
having NMI-safe cmpxchg, so ARCH_HAS_NMI_SAFE_THIS_CPU_OPS is no
longer required in the guard.
Relax the guard accordingly so that archs which have HAVE_NMI and
ARCH_HAVE_NMI_SAFE_CMPXCHG but not ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
(e.g. sparc, powerpc on PPC64/BOOK3S) can benefit from the existing
CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC path. Without this, the css
is never queued in NMI on those archs, and the atomics staged by
account_{slab,kmem}_nmi_safe() are not drained by flush_nmi_stats().
Fixes: 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in css_rstat_updated")
Signed-off-by: Cunlong Li <shenxiaogll@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup')
| -rw-r--r-- | kernel/cgroup/rstat.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index ed60ba119c68..de816a43db9f 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -81,11 +81,10 @@ void __css_rstat_updated(struct cgroup_subsys_state *css, int cpu) lockdep_assert_preemption_disabled(); /* - * For archs withnot nmi safe cmpxchg or percpu ops support, ignore - * the requests from nmi context. + * The lockless insertion below relies on NMI-safe cmpxchg; + * bail out in NMI on archs that don't provide it. */ - if ((!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) || - !IS_ENABLED(CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS)) && in_nmi()) + if (!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) && in_nmi()) return; rstatc = css_rstat_cpu(css, cpu); |