| Message ID | 20240528141341.rz_rytN_@linutronix.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] memcg: Remove the lockdep assert from __mod_objcg_mlstate(). | expand |
On 5/28/24 4:13 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 __mod_memcg_lruvec_state() and > does not require yet another check. > > 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@linutronix.de > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Vlastimil Babka <vbabka@suse.cz> mm-hotfixes as it's a rc1 regression > --- > 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);
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@linutronix.de > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > --- > 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);
On 5/28/24 4:59 PM, Shakeel Butt wrote: > 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? It only does something with CONFIG_DEBUG_VM_IRQSOFF and that's disabled by dependencies on PREEMPT_RT :) >> >> 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@linutronix.de >> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> >> --- >> 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);
On 2024-05-28 07:59:57 [-0700], Shakeel Butt wrote: > 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? we have the following in the header file: | #ifdef CONFIG_DEBUG_VM_IRQSOFF | #define VM_WARN_ON_IRQS_ENABLED() WARN_ON_ONCE(!irqs_disabled()) | #else | #define VM_WARN_ON_IRQS_ENABLED() do { } while (0) | #endif and this in Kconfig: | config DEBUG_VM_IRQSOFF | def_bool DEBUG_VM && !PREEMPT_RT | which means on PREEMPT_RT we end up with "do {…" Sebastian
On Tue, May 28, 2024 at 05:08:56PM GMT, Sebastian Andrzej Siewior wrote: > On 2024-05-28 07:59:57 [-0700], Shakeel Butt wrote: > > 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? > > we have the following in the header file: > > | #ifdef CONFIG_DEBUG_VM_IRQSOFF > | #define VM_WARN_ON_IRQS_ENABLED() WARN_ON_ONCE(!irqs_disabled()) > | #else > | #define VM_WARN_ON_IRQS_ENABLED() do { } while (0) > | #endif > > and this in Kconfig: > | config DEBUG_VM_IRQSOFF > | def_bool DEBUG_VM && !PREEMPT_RT > | > > which means on PREEMPT_RT we end up with "do {…" Thanks for the explanation.
On Tue, May 28, 2024 at 05:07:06PM GMT, Vlastimil Babka (SUSE) wrote: > On 5/28/24 4:59 PM, Shakeel Butt wrote: > > 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? > > It only does something with CONFIG_DEBUG_VM_IRQSOFF and that's disabled by > dependencies on PREEMPT_RT :) Thanks for the explanation.
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. > > 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@linutronix.de > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
On Tue 28-05-24 16:13:41, 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. > > 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@linutronix.de > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Michal Hocko <mhocko@suse.com>
--- 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 __mod_memcg_lruvec_state() and does not require yet another check. 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@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- 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(-)