* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-25 9:43 ` [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg Muchun Song
@ 2024-07-25 15:58 ` Shakeel Butt
2024-07-25 17:39 ` Roman Gushchin
` (2 subsequent siblings)
3 siblings, 0 replies; 9+ messages in thread
From: Shakeel Butt @ 2024-07-25 15:58 UTC (permalink / raw)
To: Muchun Song
Cc: hannes, mhocko, roman.gushchin, muchun.song, akpm, vbabka,
cgroups, linux-mm, linux-kernel
On Thu, Jul 25, 2024 at 05:43:30PM GMT, Muchun Song wrote:
> The obj_cgroup_memcg() is supposed to safe to prevent the returned
> memory cgroup from being freed only when the caller is holding the
> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
> ignore thoes conditions when users call some upper APIs which call
> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
> the link below). So it is better to add lockdep assertion to
> obj_cgroup_memcg() to find those issues ASAP.
>
> Because there is no user of obj_cgroup_memcg() holding objcg_lock
> to make the returned memory cgroup safe, do not add objcg_lock
> assertion (We should export objcg_lock if we really want to do).
> Additionally, this is some internal implementation detail of memcg
> and should not be accessible outside memcg code.
>
> Some users like __mem_cgroup_uncharge() do not care the lifetime
> of the returned memory cgroup, which just want to know if the
> folio is charged to a memory cgroup, therefore, they do not need
> to hold the needed locks. In which case, introduce a new helper
> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
> could eliminate a memory access of objcg->memcg for kmem, actually,
> a really small gain.
>
> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-25 9:43 ` [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg Muchun Song
2024-07-25 15:58 ` Shakeel Butt
@ 2024-07-25 17:39 ` Roman Gushchin
2024-07-26 8:09 ` Vlastimil Babka (SUSE)
2024-07-30 18:52 ` Marek Szyprowski
3 siblings, 0 replies; 9+ messages in thread
From: Roman Gushchin @ 2024-07-25 17:39 UTC (permalink / raw)
To: Muchun Song
Cc: hannes, mhocko, shakeel.butt, muchun.song, akpm, vbabka, cgroups,
linux-mm, linux-kernel
On Thu, Jul 25, 2024 at 05:43:30PM +0800, Muchun Song wrote:
> The obj_cgroup_memcg() is supposed to safe to prevent the returned
> memory cgroup from being freed only when the caller is holding the
> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
> ignore thoes conditions when users call some upper APIs which call
> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
> the link below). So it is better to add lockdep assertion to
> obj_cgroup_memcg() to find those issues ASAP.
>
> Because there is no user of obj_cgroup_memcg() holding objcg_lock
> to make the returned memory cgroup safe, do not add objcg_lock
> assertion (We should export objcg_lock if we really want to do).
> Additionally, this is some internal implementation detail of memcg
> and should not be accessible outside memcg code.
>
> Some users like __mem_cgroup_uncharge() do not care the lifetime
> of the returned memory cgroup, which just want to know if the
> folio is charged to a memory cgroup, therefore, they do not need
> to hold the needed locks. In which case, introduce a new helper
> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
> could eliminate a memory access of objcg->memcg for kmem, actually,
> a really small gain.
>
> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Thanks!
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-25 9:43 ` [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg Muchun Song
2024-07-25 15:58 ` Shakeel Butt
2024-07-25 17:39 ` Roman Gushchin
@ 2024-07-26 8:09 ` Vlastimil Babka (SUSE)
2024-07-30 18:52 ` Marek Szyprowski
3 siblings, 0 replies; 9+ messages in thread
From: Vlastimil Babka (SUSE) @ 2024-07-26 8:09 UTC (permalink / raw)
To: Muchun Song, hannes, mhocko, roman.gushchin, shakeel.butt,
muchun.song, akpm
Cc: cgroups, linux-mm, linux-kernel
On 7/25/24 11:43 AM, Muchun Song wrote:
> The obj_cgroup_memcg() is supposed to safe to prevent the returned
> memory cgroup from being freed only when the caller is holding the
> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
> ignore thoes conditions when users call some upper APIs which call
> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
> the link below). So it is better to add lockdep assertion to
> obj_cgroup_memcg() to find those issues ASAP.
>
> Because there is no user of obj_cgroup_memcg() holding objcg_lock
> to make the returned memory cgroup safe, do not add objcg_lock
> assertion (We should export objcg_lock if we really want to do).
> Additionally, this is some internal implementation detail of memcg
> and should not be accessible outside memcg code.
>
> Some users like __mem_cgroup_uncharge() do not care the lifetime
> of the returned memory cgroup, which just want to know if the
> folio is charged to a memory cgroup, therefore, they do not need
> to hold the needed locks. In which case, introduce a new helper
> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
> could eliminate a memory access of objcg->memcg for kmem, actually,
> a really small gain.
>
> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> v3:
> - Use lockdep_assert_once(Vlastimil).
>
> v2:
> - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt).
>
> include/linux/memcontrol.h | 20 +++++++++++++++++---
> mm/memcontrol.c | 6 +++---
> 2 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index fc94879db4dff..95f823deafeca 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -360,11 +360,11 @@ static inline bool folio_memcg_kmem(struct folio *folio);
> * After the initialization objcg->memcg is always pointing at
> * a valid memcg, but can be atomically swapped to the parent memcg.
> *
> - * The caller must ensure that the returned memcg won't be released:
> - * e.g. acquire the rcu_read_lock or css_set_lock.
> + * The caller must ensure that the returned memcg won't be released.
> */
> static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
> {
> + lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
> return READ_ONCE(objcg->memcg);
> }
>
> @@ -438,6 +438,19 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
> return __folio_memcg(folio);
> }
>
> +/*
> + * folio_memcg_charged - If a folio is charged to a memory cgroup.
> + * @folio: Pointer to the folio.
> + *
> + * Returns true if folio is charged to a memory cgroup, otherwise returns false.
> + */
> +static inline bool folio_memcg_charged(struct folio *folio)
> +{
> + if (folio_memcg_kmem(folio))
> + return __folio_objcg(folio) != NULL;
> + return __folio_memcg(folio) != NULL;
> +}
> +
> /**
> * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
> * @folio: Pointer to the folio.
> @@ -454,7 +467,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
> unsigned long memcg_data = READ_ONCE(folio->memcg_data);
>
> VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
> - WARN_ON_ONCE(!rcu_read_lock_held());
>
> if (memcg_data & MEMCG_DATA_KMEM) {
> struct obj_cgroup *objcg;
> @@ -463,6 +475,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
> return obj_cgroup_memcg(objcg);
> }
>
> + WARN_ON_ONCE(!rcu_read_lock_held());
> +
> return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
> }
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 622d4544edd24..3da0284573857 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2366,7 +2366,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
>
> static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
> {
> - VM_BUG_ON_FOLIO(folio_memcg(folio), folio);
> + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio);
> /*
> * Any of the following ensures page's memcg stability:
> *
> @@ -4617,7 +4617,7 @@ void __mem_cgroup_uncharge(struct folio *folio)
> struct uncharge_gather ug;
>
> /* Don't touch folio->lru of any random page, pre-check: */
> - if (!folio_memcg(folio))
> + if (!folio_memcg_charged(folio))
> return;
>
> uncharge_gather_clear(&ug);
> @@ -4662,7 +4662,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
> return;
>
> /* Page cache replacement: new folio already charged? */
> - if (folio_memcg(new))
> + if (folio_memcg_charged(new))
> return;
>
> memcg = folio_memcg(old);
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-25 9:43 ` [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg Muchun Song
` (2 preceding siblings ...)
2024-07-26 8:09 ` Vlastimil Babka (SUSE)
@ 2024-07-30 18:52 ` Marek Szyprowski
2024-07-30 20:18 ` Andrew Morton
2024-07-31 7:02 ` Muchun Song
3 siblings, 2 replies; 9+ messages in thread
From: Marek Szyprowski @ 2024-07-30 18:52 UTC (permalink / raw)
To: Muchun Song, hannes, mhocko, roman.gushchin, shakeel.butt,
muchun.song, akpm, vbabka
Cc: cgroups, linux-mm, linux-kernel
On 25.07.2024 11:43, Muchun Song wrote:
> The obj_cgroup_memcg() is supposed to safe to prevent the returned
> memory cgroup from being freed only when the caller is holding the
> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
> ignore thoes conditions when users call some upper APIs which call
> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
> the link below). So it is better to add lockdep assertion to
> obj_cgroup_memcg() to find those issues ASAP.
>
> Because there is no user of obj_cgroup_memcg() holding objcg_lock
> to make the returned memory cgroup safe, do not add objcg_lock
> assertion (We should export objcg_lock if we really want to do).
> Additionally, this is some internal implementation detail of memcg
> and should not be accessible outside memcg code.
>
> Some users like __mem_cgroup_uncharge() do not care the lifetime
> of the returned memory cgroup, which just want to know if the
> folio is charged to a memory cgroup, therefore, they do not need
> to hold the needed locks. In which case, introduce a new helper
> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
> could eliminate a memory access of objcg->memcg for kmem, actually,
> a really small gain.
>
> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
This patch landed in today's linux-next as commit 230b2f1f31b9 ("mm:
kmem: add lockdep assertion to obj_cgroup_memcg"). I my tests I found
that it triggers the following warning on Debian bookworm/sid system
image running under QEMU RISCV64:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at include/linux/memcontrol.h:373
mem_cgroup_from_slab_obj+0x13e/0x1ea
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: systemd Not tainted 6.10.0+ #15154
Hardware name: riscv-virtio,qemu (DT)
epc : mem_cgroup_from_slab_obj+0x13e/0x1ea
ra : mem_cgroup_from_slab_obj+0x13c/0x1ea
...
[<ffffffff80257256>] mem_cgroup_from_slab_obj+0x13e/0x1ea
[<ffffffff801f0b3e>] list_lru_del_obj+0xa6/0xc2
[<ffffffff8027c6c6>] d_lru_del+0x8c/0xa4
[<ffffffff8027da60>] __dentry_kill+0x15e/0x17a
[<ffffffff8027ec3c>] dput.part.0+0x242/0x3e6
[<ffffffff8027edee>] dput+0xe/0x18
[<ffffffff8027324c>] lookup_fast+0x80/0xce
[<ffffffff80273e28>] walk_component+0x20/0x13c
[<ffffffff802747e2>] path_lookupat+0x64/0x16c
[<ffffffff80274bf4>] filename_lookup+0x76/0x122
[<ffffffff80274d80>] user_path_at+0x30/0x4a
[<ffffffff802d12bc>] __riscv_sys_name_to_handle_at+0x52/0x1d8
[<ffffffff80b60324>] do_trap_ecall_u+0x14e/0x1da
[<ffffffff80b6c546>] handle_exception+0xca/0xd6
irq event stamp: 198187
hardirqs last enabled at (198187): [<ffffffff8028ca9e>]
lookup_mnt+0x186/0x308
hardirqs last disabled at (198186): [<ffffffff8028ca74>]
lookup_mnt+0x15c/0x308
softirqs last enabled at (198172): [<ffffffff800e34f6>]
cgroup_apply_control_enable+0x1f6/0x2fc
softirqs last disabled at (198170): [<ffffffff800e34d8>]
cgroup_apply_control_enable+0x1d8/0x2fc
---[ end trace 0000000000000000 ]---
Similar warning appears on ARM64 Debian bookworm system. Reverting it on
top of linux-next hides the issue, but I assume this is not the best way
to fix it.
I'm testing kernel built from riscv/defconfig with PROVE_LOCKING,
DEBUG_ATOMIC_SLEEP, DEBUG_DRIVER and DEBUG_DEVRES options enabled.
> ---
> v3:
> - Use lockdep_assert_once(Vlastimil).
>
> v2:
> - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt).
>
> include/linux/memcontrol.h | 20 +++++++++++++++++---
> mm/memcontrol.c | 6 +++---
> 2 files changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index fc94879db4dff..95f823deafeca 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -360,11 +360,11 @@ static inline bool folio_memcg_kmem(struct folio *folio);
> * After the initialization objcg->memcg is always pointing at
> * a valid memcg, but can be atomically swapped to the parent memcg.
> *
> - * The caller must ensure that the returned memcg won't be released:
> - * e.g. acquire the rcu_read_lock or css_set_lock.
> + * The caller must ensure that the returned memcg won't be released.
> */
> static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
> {
> + lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
> return READ_ONCE(objcg->memcg);
> }
>
> @@ -438,6 +438,19 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
> return __folio_memcg(folio);
> }
>
> +/*
> + * folio_memcg_charged - If a folio is charged to a memory cgroup.
> + * @folio: Pointer to the folio.
> + *
> + * Returns true if folio is charged to a memory cgroup, otherwise returns false.
> + */
> +static inline bool folio_memcg_charged(struct folio *folio)
> +{
> + if (folio_memcg_kmem(folio))
> + return __folio_objcg(folio) != NULL;
> + return __folio_memcg(folio) != NULL;
> +}
> +
> /**
> * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
> * @folio: Pointer to the folio.
> @@ -454,7 +467,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
> unsigned long memcg_data = READ_ONCE(folio->memcg_data);
>
> VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
> - WARN_ON_ONCE(!rcu_read_lock_held());
>
> if (memcg_data & MEMCG_DATA_KMEM) {
> struct obj_cgroup *objcg;
> @@ -463,6 +475,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
> return obj_cgroup_memcg(objcg);
> }
>
> + WARN_ON_ONCE(!rcu_read_lock_held());
> +
> return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
> }
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 622d4544edd24..3da0284573857 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2366,7 +2366,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
>
> static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
> {
> - VM_BUG_ON_FOLIO(folio_memcg(folio), folio);
> + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio);
> /*
> * Any of the following ensures page's memcg stability:
> *
> @@ -4617,7 +4617,7 @@ void __mem_cgroup_uncharge(struct folio *folio)
> struct uncharge_gather ug;
>
> /* Don't touch folio->lru of any random page, pre-check: */
> - if (!folio_memcg(folio))
> + if (!folio_memcg_charged(folio))
> return;
>
> uncharge_gather_clear(&ug);
> @@ -4662,7 +4662,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
> return;
>
> /* Page cache replacement: new folio already charged? */
> - if (folio_memcg(new))
> + if (folio_memcg_charged(new))
> return;
>
> memcg = folio_memcg(old);
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-30 18:52 ` Marek Szyprowski
@ 2024-07-30 20:18 ` Andrew Morton
2024-07-31 6:53 ` Muchun Song
2024-07-31 7:02 ` Muchun Song
1 sibling, 1 reply; 9+ messages in thread
From: Andrew Morton @ 2024-07-30 20:18 UTC (permalink / raw)
To: Marek Szyprowski
Cc: Muchun Song, hannes, mhocko, roman.gushchin, shakeel.butt,
muchun.song, vbabka, cgroups, linux-mm, linux-kernel
On Tue, 30 Jul 2024 20:52:04 +0200 Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> This patch landed in today's linux-next as commit 230b2f1f31b9 ("mm:
> kmem: add lockdep assertion to obj_cgroup_memcg"). I my tests I found
> that it triggers the following warning on Debian bookworm/sid system
> image running under QEMU RISCV64:
Thanks. I'll drop the patch while this gets sorted out, to be nice to
linux-next users.
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-30 20:18 ` Andrew Morton
@ 2024-07-31 6:53 ` Muchun Song
0 siblings, 0 replies; 9+ messages in thread
From: Muchun Song @ 2024-07-31 6:53 UTC (permalink / raw)
To: Andrew Morton
Cc: Marek Szyprowski, Muchun Song, Johannes Weiner, Michal Hocko,
Roman Gushchin, Shakeel Butt, Vlastimil Babka, cgroups,
Linux Memory Management List, LKML
> On Jul 31, 2024, at 04:18, Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Tue, 30 Jul 2024 20:52:04 +0200 Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>
>> This patch landed in today's linux-next as commit 230b2f1f31b9 ("mm:
>> kmem: add lockdep assertion to obj_cgroup_memcg"). I my tests I found
>> that it triggers the following warning on Debian bookworm/sid system
>> image running under QEMU RISCV64:
>
> Thanks. I'll drop the patch while this gets sorted out, to be nice to
> linux-next users.
Hi Andrew,
Please pick up this patch first [1], it is a fix for the above issue.
[1] https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
Thanks.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-30 18:52 ` Marek Szyprowski
2024-07-30 20:18 ` Andrew Morton
@ 2024-07-31 7:02 ` Muchun Song
2024-07-31 8:09 ` Marek Szyprowski
1 sibling, 1 reply; 9+ messages in thread
From: Muchun Song @ 2024-07-31 7:02 UTC (permalink / raw)
To: Marek Szyprowski
Cc: Muchun Song, Johannes Weiner, Michal Hocko, Roman Gushchin,
Shakeel Butt, Andrew Morton, vbabka, cgroups, linux-mm,
linux-kernel
> On Jul 31, 2024, at 02:52, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>
> On 25.07.2024 11:43, Muchun Song wrote:
>> The obj_cgroup_memcg() is supposed to safe to prevent the returned
>> memory cgroup from being freed only when the caller is holding the
>> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
>> ignore thoes conditions when users call some upper APIs which call
>> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
>> the link below). So it is better to add lockdep assertion to
>> obj_cgroup_memcg() to find those issues ASAP.
>>
>> Because there is no user of obj_cgroup_memcg() holding objcg_lock
>> to make the returned memory cgroup safe, do not add objcg_lock
>> assertion (We should export objcg_lock if we really want to do).
>> Additionally, this is some internal implementation detail of memcg
>> and should not be accessible outside memcg code.
>>
>> Some users like __mem_cgroup_uncharge() do not care the lifetime
>> of the returned memory cgroup, which just want to know if the
>> folio is charged to a memory cgroup, therefore, they do not need
>> to hold the needed locks. In which case, introduce a new helper
>> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
>> could eliminate a memory access of objcg->memcg for kmem, actually,
>> a really small gain.
>>
>> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>
> This patch landed in today's linux-next as commit 230b2f1f31b9 ("mm:
> kmem: add lockdep assertion to obj_cgroup_memcg"). I my tests I found
> that it triggers the following warning on Debian bookworm/sid system
> image running under QEMU RISCV64:
Thanks for your report.
I'd like to say excellent since it indeed indicates this patch works
well. Your report is actually a bug that I fixed it in [1] but not
related to this patch.
[1] https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
>
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at include/linux/memcontrol.h:373
> mem_cgroup_from_slab_obj+0x13e/0x1ea
> Modules linked in:
> CPU: 0 UID: 0 PID: 1 Comm: systemd Not tainted 6.10.0+ #15154
> Hardware name: riscv-virtio,qemu (DT)
> epc : mem_cgroup_from_slab_obj+0x13e/0x1ea
> ra : mem_cgroup_from_slab_obj+0x13c/0x1ea
> ...
> [<ffffffff80257256>] mem_cgroup_from_slab_obj+0x13e/0x1ea
> [<ffffffff801f0b3e>] list_lru_del_obj+0xa6/0xc2
> [<ffffffff8027c6c6>] d_lru_del+0x8c/0xa4
> [<ffffffff8027da60>] __dentry_kill+0x15e/0x17a
> [<ffffffff8027ec3c>] dput.part.0+0x242/0x3e6
> [<ffffffff8027edee>] dput+0xe/0x18
> [<ffffffff8027324c>] lookup_fast+0x80/0xce
> [<ffffffff80273e28>] walk_component+0x20/0x13c
> [<ffffffff802747e2>] path_lookupat+0x64/0x16c
> [<ffffffff80274bf4>] filename_lookup+0x76/0x122
> [<ffffffff80274d80>] user_path_at+0x30/0x4a
> [<ffffffff802d12bc>] __riscv_sys_name_to_handle_at+0x52/0x1d8
> [<ffffffff80b60324>] do_trap_ecall_u+0x14e/0x1da
> [<ffffffff80b6c546>] handle_exception+0xca/0xd6
> irq event stamp: 198187
> hardirqs last enabled at (198187): [<ffffffff8028ca9e>]
> lookup_mnt+0x186/0x308
> hardirqs last disabled at (198186): [<ffffffff8028ca74>]
> lookup_mnt+0x15c/0x308
> softirqs last enabled at (198172): [<ffffffff800e34f6>]
> cgroup_apply_control_enable+0x1f6/0x2fc
> softirqs last disabled at (198170): [<ffffffff800e34d8>]
> cgroup_apply_control_enable+0x1d8/0x2fc
> ---[ end trace 0000000000000000 ]---
>
> Similar warning appears on ARM64 Debian bookworm system. Reverting it on
> top of linux-next hides the issue, but I assume this is not the best way
> to fix it.
>
> I'm testing kernel built from riscv/defconfig with PROVE_LOCKING,
> DEBUG_ATOMIC_SLEEP, DEBUG_DRIVER and DEBUG_DEVRES options enabled.
>
>> ---
>> v3:
>> - Use lockdep_assert_once(Vlastimil).
>>
>> v2:
>> - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt).
>>
>> include/linux/memcontrol.h | 20 +++++++++++++++++---
>> mm/memcontrol.c | 6 +++---
>> 2 files changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index fc94879db4dff..95f823deafeca 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -360,11 +360,11 @@ static inline bool folio_memcg_kmem(struct folio *folio);
>> * After the initialization objcg->memcg is always pointing at
>> * a valid memcg, but can be atomically swapped to the parent memcg.
>> *
>> - * The caller must ensure that the returned memcg won't be released:
>> - * e.g. acquire the rcu_read_lock or css_set_lock.
>> + * The caller must ensure that the returned memcg won't be released.
>> */
>> static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
>> {
>> + lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
>> return READ_ONCE(objcg->memcg);
>> }
>>
>> @@ -438,6 +438,19 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
>> return __folio_memcg(folio);
>> }
>>
>> +/*
>> + * folio_memcg_charged - If a folio is charged to a memory cgroup.
>> + * @folio: Pointer to the folio.
>> + *
>> + * Returns true if folio is charged to a memory cgroup, otherwise returns false.
>> + */
>> +static inline bool folio_memcg_charged(struct folio *folio)
>> +{
>> + if (folio_memcg_kmem(folio))
>> + return __folio_objcg(folio) != NULL;
>> + return __folio_memcg(folio) != NULL;
>> +}
>> +
>> /**
>> * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
>> * @folio: Pointer to the folio.
>> @@ -454,7 +467,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
>> unsigned long memcg_data = READ_ONCE(folio->memcg_data);
>>
>> VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
>> - WARN_ON_ONCE(!rcu_read_lock_held());
>>
>> if (memcg_data & MEMCG_DATA_KMEM) {
>> struct obj_cgroup *objcg;
>> @@ -463,6 +475,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
>> return obj_cgroup_memcg(objcg);
>> }
>>
>> + WARN_ON_ONCE(!rcu_read_lock_held());
>> +
>> return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
>> }
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 622d4544edd24..3da0284573857 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -2366,7 +2366,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
>>
>> static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
>> {
>> - VM_BUG_ON_FOLIO(folio_memcg(folio), folio);
>> + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio);
>> /*
>> * Any of the following ensures page's memcg stability:
>> *
>> @@ -4617,7 +4617,7 @@ void __mem_cgroup_uncharge(struct folio *folio)
>> struct uncharge_gather ug;
>>
>> /* Don't touch folio->lru of any random page, pre-check: */
>> - if (!folio_memcg(folio))
>> + if (!folio_memcg_charged(folio))
>> return;
>>
>> uncharge_gather_clear(&ug);
>> @@ -4662,7 +4662,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
>> return;
>>
>> /* Page cache replacement: new folio already charged? */
>> - if (folio_memcg(new))
>> + if (folio_memcg_charged(new))
>> return;
>>
>> memcg = folio_memcg(old);
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH v3] mm: kmem: add lockdep assertion to obj_cgroup_memcg
2024-07-31 7:02 ` Muchun Song
@ 2024-07-31 8:09 ` Marek Szyprowski
0 siblings, 0 replies; 9+ messages in thread
From: Marek Szyprowski @ 2024-07-31 8:09 UTC (permalink / raw)
To: Muchun Song
Cc: Muchun Song, Johannes Weiner, Michal Hocko, Roman Gushchin,
Shakeel Butt, Andrew Morton, vbabka, cgroups, linux-mm,
linux-kernel
On 31.07.2024 09:02, Muchun Song wrote:
>> On Jul 31, 2024, at 02:52, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>>
>> On 25.07.2024 11:43, Muchun Song wrote:
>>> The obj_cgroup_memcg() is supposed to safe to prevent the returned
>>> memory cgroup from being freed only when the caller is holding the
>>> rcu read lock or objcg_lock or cgroup_mutex. It is very easy to
>>> ignore thoes conditions when users call some upper APIs which call
>>> obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See
>>> the link below). So it is better to add lockdep assertion to
>>> obj_cgroup_memcg() to find those issues ASAP.
>>>
>>> Because there is no user of obj_cgroup_memcg() holding objcg_lock
>>> to make the returned memory cgroup safe, do not add objcg_lock
>>> assertion (We should export objcg_lock if we really want to do).
>>> Additionally, this is some internal implementation detail of memcg
>>> and should not be accessible outside memcg code.
>>>
>>> Some users like __mem_cgroup_uncharge() do not care the lifetime
>>> of the returned memory cgroup, which just want to know if the
>>> folio is charged to a memory cgroup, therefore, they do not need
>>> to hold the needed locks. In which case, introduce a new helper
>>> folio_memcg_charged() to do this. Compare it to folio_memcg(), it
>>> could eliminate a memory access of objcg->memcg for kmem, actually,
>>> a really small gain.
>>>
>>> Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
>>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>> This patch landed in today's linux-next as commit 230b2f1f31b9 ("mm:
>> kmem: add lockdep assertion to obj_cgroup_memcg"). I my tests I found
>> that it triggers the following warning on Debian bookworm/sid system
>> image running under QEMU RISCV64:
> Thanks for your report.
>
> I'd like to say excellent since it indeed indicates this patch works
> well. Your report is actually a bug that I fixed it in [1] but not
> related to this patch.
>
> [1] https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/
Confirmed. Applying [1] on top of next-20240730 fixes this issue without
reverting $subject.
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 1 at include/linux/memcontrol.h:373
>> mem_cgroup_from_slab_obj+0x13e/0x1ea
>> Modules linked in:
>> CPU: 0 UID: 0 PID: 1 Comm: systemd Not tainted 6.10.0+ #15154
>> Hardware name: riscv-virtio,qemu (DT)
>> epc : mem_cgroup_from_slab_obj+0x13e/0x1ea
>> ra : mem_cgroup_from_slab_obj+0x13c/0x1ea
>> ...
>> [<ffffffff80257256>] mem_cgroup_from_slab_obj+0x13e/0x1ea
>> [<ffffffff801f0b3e>] list_lru_del_obj+0xa6/0xc2
>> [<ffffffff8027c6c6>] d_lru_del+0x8c/0xa4
>> [<ffffffff8027da60>] __dentry_kill+0x15e/0x17a
>> [<ffffffff8027ec3c>] dput.part.0+0x242/0x3e6
>> [<ffffffff8027edee>] dput+0xe/0x18
>> [<ffffffff8027324c>] lookup_fast+0x80/0xce
>> [<ffffffff80273e28>] walk_component+0x20/0x13c
>> [<ffffffff802747e2>] path_lookupat+0x64/0x16c
>> [<ffffffff80274bf4>] filename_lookup+0x76/0x122
>> [<ffffffff80274d80>] user_path_at+0x30/0x4a
>> [<ffffffff802d12bc>] __riscv_sys_name_to_handle_at+0x52/0x1d8
>> [<ffffffff80b60324>] do_trap_ecall_u+0x14e/0x1da
>> [<ffffffff80b6c546>] handle_exception+0xca/0xd6
>> irq event stamp: 198187
>> hardirqs last enabled at (198187): [<ffffffff8028ca9e>]
>> lookup_mnt+0x186/0x308
>> hardirqs last disabled at (198186): [<ffffffff8028ca74>]
>> lookup_mnt+0x15c/0x308
>> softirqs last enabled at (198172): [<ffffffff800e34f6>]
>> cgroup_apply_control_enable+0x1f6/0x2fc
>> softirqs last disabled at (198170): [<ffffffff800e34d8>]
>> cgroup_apply_control_enable+0x1d8/0x2fc
>> ---[ end trace 0000000000000000 ]---
>>
>> Similar warning appears on ARM64 Debian bookworm system. Reverting it on
>> top of linux-next hides the issue, but I assume this is not the best way
>> to fix it.
>>
>> I'm testing kernel built from riscv/defconfig with PROVE_LOCKING,
>> DEBUG_ATOMIC_SLEEP, DEBUG_DRIVER and DEBUG_DEVRES options enabled.
>>
>>> ---
>>> v3:
>>> - Use lockdep_assert_once(Vlastimil).
>>>
>>> v2:
>>> - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt).
>>>
>>> include/linux/memcontrol.h | 20 +++++++++++++++++---
>>> mm/memcontrol.c | 6 +++---
>>> 2 files changed, 20 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>>> index fc94879db4dff..95f823deafeca 100644
>>> --- a/include/linux/memcontrol.h
>>> +++ b/include/linux/memcontrol.h
>>> @@ -360,11 +360,11 @@ static inline bool folio_memcg_kmem(struct folio *folio);
>>> * After the initialization objcg->memcg is always pointing at
>>> * a valid memcg, but can be atomically swapped to the parent memcg.
>>> *
>>> - * The caller must ensure that the returned memcg won't be released:
>>> - * e.g. acquire the rcu_read_lock or css_set_lock.
>>> + * The caller must ensure that the returned memcg won't be released.
>>> */
>>> static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
>>> {
>>> + lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
>>> return READ_ONCE(objcg->memcg);
>>> }
>>>
>>> @@ -438,6 +438,19 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
>>> return __folio_memcg(folio);
>>> }
>>>
>>> +/*
>>> + * folio_memcg_charged - If a folio is charged to a memory cgroup.
>>> + * @folio: Pointer to the folio.
>>> + *
>>> + * Returns true if folio is charged to a memory cgroup, otherwise returns false.
>>> + */
>>> +static inline bool folio_memcg_charged(struct folio *folio)
>>> +{
>>> + if (folio_memcg_kmem(folio))
>>> + return __folio_objcg(folio) != NULL;
>>> + return __folio_memcg(folio) != NULL;
>>> +}
>>> +
>>> /**
>>> * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
>>> * @folio: Pointer to the folio.
>>> @@ -454,7 +467,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
>>> unsigned long memcg_data = READ_ONCE(folio->memcg_data);
>>>
>>> VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
>>> - WARN_ON_ONCE(!rcu_read_lock_held());
>>>
>>> if (memcg_data & MEMCG_DATA_KMEM) {
>>> struct obj_cgroup *objcg;
>>> @@ -463,6 +475,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
>>> return obj_cgroup_memcg(objcg);
>>> }
>>>
>>> + WARN_ON_ONCE(!rcu_read_lock_held());
>>> +
>>> return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
>>> }
>>>
>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>> index 622d4544edd24..3da0284573857 100644
>>> --- a/mm/memcontrol.c
>>> +++ b/mm/memcontrol.c
>>> @@ -2366,7 +2366,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
>>>
>>> static void commit_charge(struct folio *folio, struct mem_cgroup *memcg)
>>> {
>>> - VM_BUG_ON_FOLIO(folio_memcg(folio), folio);
>>> + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio);
>>> /*
>>> * Any of the following ensures page's memcg stability:
>>> *
>>> @@ -4617,7 +4617,7 @@ void __mem_cgroup_uncharge(struct folio *folio)
>>> struct uncharge_gather ug;
>>>
>>> /* Don't touch folio->lru of any random page, pre-check: */
>>> - if (!folio_memcg(folio))
>>> + if (!folio_memcg_charged(folio))
>>> return;
>>>
>>> uncharge_gather_clear(&ug);
>>> @@ -4662,7 +4662,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new)
>>> return;
>>>
>>> /* Page cache replacement: new folio already charged? */
>>> - if (folio_memcg(new))
>>> + if (folio_memcg_charged(new))
>>> return;
>>>
>>> memcg = folio_memcg(old);
>> Best regards
>> --
>> Marek Szyprowski, PhD
>> Samsung R&D Institute Poland
>
>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
^ permalink raw reply [flat|nested] 9+ messages in thread