+ memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch added to mm-hotfixes-unstable branch

+ memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: memcg: remove the lockdep assert from __mod_objcg_mlstate()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: memcg: remove the lockdep assert from __mod_objcg_mlstate()
Date: Tue, 28 May 2024 16:13:41 +0200

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().

Link: https://lkml.kernel.org/r/20240528141341.rz_rytN_@linutronix.de
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>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/memcontrol.c~memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate
+++ a/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);
_

Patches currently in -mm which might be from bigeasy@linutronix.de are

memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch

+ memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: memcg: remove the lockdep assert from __mod_objcg_mlstate()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: memcg: remove the lockdep assert from __mod_objcg_mlstate()
Date: Tue, 28 May 2024 16:13:41 +0200

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().

Link: https://lkml.kernel.org/r/20240528141341.rz_rytN_@linutronix.de
Link: https://lore.kernel.org/r/20240528121928.i-Gu7Jvg@linutronix.de
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>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Thomas Gleixner <tglx@linutronix.de>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/memcontrol.c~memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate
+++ a/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);
_

Patches currently in -mm which might be from bigeasy@linutronix.de are

memcg-remove-the-lockdep-assert-from-__mod_objcg_mlstate.patch