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 <[email protected]>
---
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 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 <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
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
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/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
---
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 4:13 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/[email protected]
> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
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/[email protected]
> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
> ---
> 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/[email protected]
>> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
>> ---
>> 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/[email protected]
> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Shakeel Butt <[email protected]>
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/[email protected]
> Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Michal Hocko <[email protected]>
--
Michal Hocko
SUSE Labs