On Tue, May 28, 2024 at 04:13:41PM GMT, Sebastian Andrzej Siewior wrote: > The assert was introduced in the commit cited below as an insurance that > the semantic is the same after the local_irq_save() has been removed and > the function has been made static. > > The original requirement to disable interrupt was due the modification > of per-CPU counters which require interrupts to be disabled because the > counter update operation is not atomic and some of the counters are > updated from interrupt context. > > All callers of __mod_objcg_mlstate() acquire a lock > (memcg_stock.stock_lock) which disables interrupts on !PREEMPT_RT and > the lockdep assert is satisfied. On PREEMPT_RT the interrupts are not > disabled and the assert triggers. > > The safety of the counter update is already ensured by > VM_WARN_ON_IRQS_ENABLED() which is part of __mod_memcg_lruvec_state() and > does not require yet another check. One question on VM_WARN_ON_IRQS_ENABLED() in __mod_memcg_lruvec_state(). On a PREEMPT_RT kernel with CONFIG_DEBUG_VM, will that VM_WARN_ON_IRQS_ENABLED() cause a splat or VM_WARN_ON_IRQS_ENABLED is special on PREEMPT_RT kernels? > > Remove the lockdep assert from __mod_objcg_mlstate(). > > Fixes: 91882c1617c15 ("memcg: simple cleanup of stats update functions") > Link: https://lore.kernel.org/r/20240528121928.i-Gu7Jvg@xxxxxxxxxxxxx > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > --- > On 2024-05-28 15:44:51 [+0200], Vlastimil Babka (SUSE) wrote: > > I think just s/memcg_stats_lock()/__mod_memcg_lruvec_state()/ in your > > phrasing, since we are removing the lockdep assert from path that calls > > __mod_memcg_lruvec_state() and not memcg_stats_lock()? > > Or am I missing something? > > Yeah, makes sense. > > mm/memcontrol.c | 2 -- > 1 file changed, 2 deletions(-) > > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3147,8 +3147,6 @@ static inline void __mod_objcg_mlstate(s > struct mem_cgroup *memcg; > struct lruvec *lruvec; > > - lockdep_assert_irqs_disabled(); > - > rcu_read_lock(); > memcg = obj_cgroup_memcg(objcg); > lruvec = mem_cgroup_lruvec(memcg, pgdat);