Re: [PATCH v2] memcg: Remove the lockdep assert from __mod_objcg_mlstate().

[Michal Hocko]

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@xxxxxxxxxxxxx
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

-- 
Michal Hocko
SUSE Labs