| Message ID | 20240528121928.i-Gu7Jvg@linutronix.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | memcg: Remove the lockdep assert from __mod_objcg_mlstate(). | expand |
On 5/28/24 2:19 PM, 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 memcg_stats_lock() and does > not require yet another check. I think here it's __mod_memcg_lruvec_state() doing the VM_WARN_ON_ as we don't go through memcg_stats_lock()? > Remove the lockdep assert from __mod_objcg_mlstate(). > > Fixes: 91882c1617c15 ("memcg: simple cleanup of stats update functions") > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> mm-hotfixes as it's a rc1 regression > --- > 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);
On 2024-05-28 14:34:55 [+0200], Vlastimil Babka (SUSE) wrote: > > The safety of the counter update is already ensured by > > VM_WARN_ON_IRQS_ENABLED() which is part of memcg_stats_lock() and does > > not require yet another check. > > I think here it's __mod_memcg_lruvec_state() doing the VM_WARN_ON_ as we > don't go through memcg_stats_lock()? It is either VM_WARN_ON_IRQS_ENABLED() directly as in __mod_memcg_lruvec_state() (which is special) or memcg_stats_lock(). Do you want me to rephrase this part? Sebastian
On 5/28/24 3:40 PM, Sebastian Andrzej Siewior wrote: > On 2024-05-28 14:34:55 [+0200], Vlastimil Babka (SUSE) wrote: >> > The safety of the counter update is already ensured by >> > VM_WARN_ON_IRQS_ENABLED() which is part of memcg_stats_lock() and does >> > not require yet another check. >> >> I think here it's __mod_memcg_lruvec_state() doing the VM_WARN_ON_ as we >> don't go through memcg_stats_lock()? > > It is either VM_WARN_ON_IRQS_ENABLED() directly as in > __mod_memcg_lruvec_state() (which is special) or memcg_stats_lock(). > > Do you want me to rephrase this part? 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? > Sebastian
--- 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);
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 memcg_stats_lock() and does not require yet another check. Remove the lockdep assert from __mod_objcg_mlstate(). Fixes: 91882c1617c15 ("memcg: simple cleanup of stats update functions") Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- mm/memcontrol.c | 2 -- 1 file changed, 2 deletions(-)