mm/slub.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-)
From: yangshiguang <yangshiguang@xiaomi.com>
From: yangshiguang <yangshiguang@xiaomi.com>
set_track_prepare() can incur lock recursion.
The issue is that it is called from hrtimer_start_range_ns
holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
and try to hold the per_cpu(hrtimer_bases)[n].lock.
Avoid deadlock caused by implicitly waking up kswapd by
passing in allocation flags. And the slab caller context has
preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags.
The oops looks something like:
BUG: spinlock recursion on CPU#3, swapper/3/0
lock: 0xffffff8a4bf29c80, .magic: dead4ead, .owner: swapper/3/0, .owner_cpu: 3
Hardware name: Qualcomm Technologies, Inc. Popsicle based on SM8850 (DT)
Call trace:
spin_bug+0x0
_raw_spin_lock_irqsave+0x80
hrtimer_try_to_cancel+0x94
task_contending+0x10c
enqueue_dl_entity+0x2a4
dl_server_start+0x74
enqueue_task_fair+0x568
enqueue_task+0xac
do_activate_task+0x14c
ttwu_do_activate+0xcc
try_to_wake_up+0x6c8
default_wake_function+0x20
autoremove_wake_function+0x1c
__wake_up+0xac
wakeup_kswapd+0x19c
wake_all_kswapds+0x78
__alloc_pages_slowpath+0x1ac
__alloc_pages_noprof+0x298
stack_depot_save_flags+0x6b0
stack_depot_save+0x14
set_track_prepare+0x5c
___slab_alloc+0xccc
__kmalloc_cache_noprof+0x470
__set_page_owner+0x2bc
post_alloc_hook[jt]+0x1b8
prep_new_page+0x28
get_page_from_freelist+0x1edc
__alloc_pages_noprof+0x13c
alloc_slab_page+0x244
allocate_slab+0x7c
___slab_alloc+0x8e8
kmem_cache_alloc_noprof+0x450
debug_objects_fill_pool+0x22c
debug_object_activate+0x40
enqueue_hrtimer[jt]+0xdc
hrtimer_start_range_ns+0x5f8
...
Signed-off-by: yangshiguang <yangshiguang@xiaomi.com>
Fixes: 5cf909c553e9 ("mm/slub: use stackdepot to save stack trace in objects")
Cc: stable@vger.kernel.org
---
v1 -> v2:
propagate gfp flags to set_track_prepare()
v2 -> v3:
Remove the gfp restriction in set_track_prepare()
v3 -> v4:
Re-describe the comments in set_track_prepare.
[1]https://lore.kernel.org/all/20250801065121.876793-1-yangshiguang1011@163.com/
[2]https://lore.kernel.org/all/20250814111641.380629-2-yangshiguang1011@163.com/
[3]https://lore.kernel.org/all/20250825121737.2535732-1-yangshiguang1011@163.com/
---
mm/slub.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 30003763d224..b0af51a5321b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -962,19 +962,25 @@ static struct track *get_track(struct kmem_cache *s, void *object,
}
#ifdef CONFIG_STACKDEPOT
-static noinline depot_stack_handle_t set_track_prepare(void)
+static noinline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
{
depot_stack_handle_t handle;
unsigned long entries[TRACK_ADDRS_COUNT];
unsigned int nr_entries;
+ /*
+ * Preemption is disabled in ___slab_alloc() so we need to disallow
+ * blocking. The flags are further adjusted by gfp_nested_mask() in
+ * stack_depot itself.
+ */
+ gfp_flags &= ~(__GFP_DIRECT_RECLAIM);
nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
- handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
+ handle = stack_depot_save(entries, nr_entries, gfp_flags);
return handle;
}
#else
-static inline depot_stack_handle_t set_track_prepare(void)
+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
{
return 0;
}
@@ -996,9 +1002,9 @@ static void set_track_update(struct kmem_cache *s, void *object,
}
static __always_inline void set_track(struct kmem_cache *s, void *object,
- enum track_item alloc, unsigned long addr)
+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags)
{
- depot_stack_handle_t handle = set_track_prepare();
+ depot_stack_handle_t handle = set_track_prepare(gfp_flags);
set_track_update(s, object, alloc, addr, handle);
}
@@ -1921,9 +1927,9 @@ static inline bool free_debug_processing(struct kmem_cache *s,
static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
static inline int check_object(struct kmem_cache *s, struct slab *slab,
void *object, u8 val) { return 1; }
-static inline depot_stack_handle_t set_track_prepare(void) { return 0; }
+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }
static inline void set_track(struct kmem_cache *s, void *object,
- enum track_item alloc, unsigned long addr) {}
+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}
static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
struct slab *slab) {}
static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
@@ -3878,7 +3884,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
* tracking info and return the object.
*/
if (s->flags & SLAB_STORE_USER)
- set_track(s, freelist, TRACK_ALLOC, addr);
+ set_track(s, freelist, TRACK_ALLOC, addr, gfpflags);
return freelist;
}
@@ -3910,7 +3916,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
goto new_objects;
if (s->flags & SLAB_STORE_USER)
- set_track(s, freelist, TRACK_ALLOC, addr);
+ set_track(s, freelist, TRACK_ALLOC, addr, gfpflags);
return freelist;
}
@@ -4422,7 +4428,7 @@ static noinline void free_to_partial_list(
depot_stack_handle_t handle = 0;
if (s->flags & SLAB_STORE_USER)
- handle = set_track_prepare();
+ handle = set_track_prepare(__GFP_NOWARN);
spin_lock_irqsave(&n->list_lock, flags);
--
2.43.0On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote:
> From: yangshiguang <yangshiguang@xiaomi.com>
>
> From: yangshiguang <yangshiguang@xiaomi.com>
>
Duplicate lines.
> set_track_prepare() can incur lock recursion.
> The issue is that it is called from hrtimer_start_range_ns
> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
> and try to hold the per_cpu(hrtimer_bases)[n].lock.
>
> Avoid deadlock caused by implicitly waking up kswapd by
> passing in allocation flags. And the slab caller context has
> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags.
>
This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off
__GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling
direct reclaim does not necessarily imply that kswapd will be disabled as
well.
Are you meaning to clear __GFP_RECLAIM in set_track_prepare()?
> The oops looks something like:
>
> BUG: spinlock recursion on CPU#3, swapper/3/0
> lock: 0xffffff8a4bf29c80, .magic: dead4ead, .owner: swapper/3/0, .owner_cpu: 3
> Hardware name: Qualcomm Technologies, Inc. Popsicle based on SM8850 (DT)
> Call trace:
> spin_bug+0x0
> _raw_spin_lock_irqsave+0x80
> hrtimer_try_to_cancel+0x94
> task_contending+0x10c
> enqueue_dl_entity+0x2a4
> dl_server_start+0x74
> enqueue_task_fair+0x568
> enqueue_task+0xac
> do_activate_task+0x14c
> ttwu_do_activate+0xcc
> try_to_wake_up+0x6c8
> default_wake_function+0x20
> autoremove_wake_function+0x1c
> __wake_up+0xac
> wakeup_kswapd+0x19c
> wake_all_kswapds+0x78
> __alloc_pages_slowpath+0x1ac
> __alloc_pages_noprof+0x298
> stack_depot_save_flags+0x6b0
> stack_depot_save+0x14
> set_track_prepare+0x5c
> ___slab_alloc+0xccc
> __kmalloc_cache_noprof+0x470
> __set_page_owner+0x2bc
> post_alloc_hook[jt]+0x1b8
> prep_new_page+0x28
> get_page_from_freelist+0x1edc
> __alloc_pages_noprof+0x13c
> alloc_slab_page+0x244
> allocate_slab+0x7c
> ___slab_alloc+0x8e8
> kmem_cache_alloc_noprof+0x450
> debug_objects_fill_pool+0x22c
> debug_object_activate+0x40
> enqueue_hrtimer[jt]+0xdc
> hrtimer_start_range_ns+0x5f8
> ...
>
> Signed-off-by: yangshiguang <yangshiguang@xiaomi.com>
> Fixes: 5cf909c553e9 ("mm/slub: use stackdepot to save stack trace in objects")
> Cc: stable@vger.kernel.org
> ---
>
> v1 -> v2:
> propagate gfp flags to set_track_prepare()
> v2 -> v3:
> Remove the gfp restriction in set_track_prepare()
> v3 -> v4:
> Re-describe the comments in set_track_prepare.
>
> [1]https://lore.kernel.org/all/20250801065121.876793-1-yangshiguang1011@163.com/
> [2]https://lore.kernel.org/all/20250814111641.380629-2-yangshiguang1011@163.com/
> [3]https://lore.kernel.org/all/20250825121737.2535732-1-yangshiguang1011@163.com/
> ---
> mm/slub.c | 26 ++++++++++++++++----------
> 1 file changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 30003763d224..b0af51a5321b 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -962,19 +962,25 @@ static struct track *get_track(struct kmem_cache *s, void *object,
> }
>
> #ifdef CONFIG_STACKDEPOT
> -static noinline depot_stack_handle_t set_track_prepare(void)
> +static noinline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
> {
> depot_stack_handle_t handle;
> unsigned long entries[TRACK_ADDRS_COUNT];
> unsigned int nr_entries;
> + /*
> + * Preemption is disabled in ___slab_alloc() so we need to disallow
> + * blocking. The flags are further adjusted by gfp_nested_mask() in
> + * stack_depot itself.
> + */
> + gfp_flags &= ~(__GFP_DIRECT_RECLAIM);
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
> - handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
> + handle = stack_depot_save(entries, nr_entries, gfp_flags);
>
> return handle;
> }
> #else
> -static inline depot_stack_handle_t set_track_prepare(void)
> +static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
> {
> return 0;
> }
> @@ -996,9 +1002,9 @@ static void set_track_update(struct kmem_cache *s, void *object,
> }
>
> static __always_inline void set_track(struct kmem_cache *s, void *object,
> - enum track_item alloc, unsigned long addr)
> + enum track_item alloc, unsigned long addr, gfp_t gfp_flags)
> {
> - depot_stack_handle_t handle = set_track_prepare();
> + depot_stack_handle_t handle = set_track_prepare(gfp_flags);
>
> set_track_update(s, object, alloc, addr, handle);
> }
> @@ -1921,9 +1927,9 @@ static inline bool free_debug_processing(struct kmem_cache *s,
> static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
> static inline int check_object(struct kmem_cache *s, struct slab *slab,
> void *object, u8 val) { return 1; }
> -static inline depot_stack_handle_t set_track_prepare(void) { return 0; }
> +static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }
> static inline void set_track(struct kmem_cache *s, void *object,
> - enum track_item alloc, unsigned long addr) {}
> + enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}
> static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
> struct slab *slab) {}
> static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
> @@ -3878,7 +3884,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> * tracking info and return the object.
> */
> if (s->flags & SLAB_STORE_USER)
> - set_track(s, freelist, TRACK_ALLOC, addr);
> + set_track(s, freelist, TRACK_ALLOC, addr, gfpflags);
>
> return freelist;
> }
> @@ -3910,7 +3916,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> goto new_objects;
>
> if (s->flags & SLAB_STORE_USER)
> - set_track(s, freelist, TRACK_ALLOC, addr);
> + set_track(s, freelist, TRACK_ALLOC, addr, gfpflags);
>
> return freelist;
> }
> @@ -4422,7 +4428,7 @@ static noinline void free_to_partial_list(
> depot_stack_handle_t handle = 0;
>
> if (s->flags & SLAB_STORE_USER)
> - handle = set_track_prepare();
> + handle = set_track_prepare(__GFP_NOWARN);
>
> spin_lock_irqsave(&n->list_lock, flags);
>
> --
> 2.43.0
>
>
On 9/1/25 09:50, David Rientjes wrote: > On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote: > >> From: yangshiguang <yangshiguang@xiaomi.com> >> >> From: yangshiguang <yangshiguang@xiaomi.com> >> > > Duplicate lines. > >> set_track_prepare() can incur lock recursion. >> The issue is that it is called from hrtimer_start_range_ns >> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled >> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare, >> and try to hold the per_cpu(hrtimer_bases)[n].lock. >> >> Avoid deadlock caused by implicitly waking up kswapd by >> passing in allocation flags. And the slab caller context has >> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags. >> > > This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off > __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling > direct reclaim does not necessarily imply that kswapd will be disabled as > well. Yeah I think the changelog should say __GFP_DIRECT_RECLAIM. > Are you meaning to clear __GFP_RECLAIM in set_track_prepare()? No because if the context context (e.g. the hrtimers) can't support __GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to set_track_prepare() so it already won't be there.
At 2025-09-01 16:15:04, "Vlastimil Babka" <vbabka@suse.cz> wrote: >On 9/1/25 09:50, David Rientjes wrote: >> On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote: >> >>> From: yangshiguang <yangshiguang@xiaomi.com> >>> >>> From: yangshiguang <yangshiguang@xiaomi.com> >>> >> >> Duplicate lines. >> >>> set_track_prepare() can incur lock recursion. >>> The issue is that it is called from hrtimer_start_range_ns >>> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled >>> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare, >>> and try to hold the per_cpu(hrtimer_bases)[n].lock. >>> >>> Avoid deadlock caused by implicitly waking up kswapd by >>> passing in allocation flags. And the slab caller context has >>> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags. >>> >> >> This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off >> __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling >> direct reclaim does not necessarily imply that kswapd will be disabled as >> well. > >Yeah I think the changelog should say __GFP_DIRECT_RECLAIM. > >> Are you meaning to clear __GFP_RECLAIM in set_track_prepare()? > >No because if the context context (e.g. the hrtimers) can't support >__GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to >set_track_prepare() so it already won't be there. Sry. Should be __GFP_DIRECT_RECLAIM. I will resend the patch.
On 9/1/25 10:29, yangshiguang wrote:
>
>
> At 2025-09-01 16:15:04, "Vlastimil Babka" <vbabka@suse.cz> wrote:
>>On 9/1/25 09:50, David Rientjes wrote:
>>> On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote:
>>>
>>>> From: yangshiguang <yangshiguang@xiaomi.com>
>>>>
>>>> From: yangshiguang <yangshiguang@xiaomi.com>
>>>>
>>>
>>> Duplicate lines.
>>>
>>>> set_track_prepare() can incur lock recursion.
>>>> The issue is that it is called from hrtimer_start_range_ns
>>>> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
>>>> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
>>>> and try to hold the per_cpu(hrtimer_bases)[n].lock.
>>>>
>>>> Avoid deadlock caused by implicitly waking up kswapd by
>>>> passing in allocation flags. And the slab caller context has
>>>> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags.
>>>>
>>>
>>> This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off
>>> __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling
>>> direct reclaim does not necessarily imply that kswapd will be disabled as
>>> well.
>>
>>Yeah I think the changelog should say __GFP_DIRECT_RECLAIM.
>>
>>> Are you meaning to clear __GFP_RECLAIM in set_track_prepare()?
>>
>>No because if the context context (e.g. the hrtimers) can't support
>>__GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to
>
>>set_track_prepare() so it already won't be there.
>
>
> Sry. Should be __GFP_DIRECT_RECLAIM. I will resend the patch.
I have adjusted it locally already. Also moved the masking of
__GFP_DIRECT_RECLAIM to ___slab_alloc itself as that's where
the preemption is disabled so it's more obvious.
Does the result look good to you?
commit 1b7052bc536650f8ca29b4f6f8682dc9f5692d16
Author: yangshiguang <yangshiguang@xiaomi.com>
Date: Sat Aug 30 10:09:46 2025 +0800
mm: slub: avoid wake up kswapd in set_track_prepare
set_track_prepare() can incur lock recursion.
The issue is that it is called from hrtimer_start_range_ns
holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
and try to hold the per_cpu(hrtimer_bases)[n].lock.
Avoid deadlock caused by implicitly waking up kswapd by passing in
allocation flags, which do not contain __GFP_KSWAPD_RECLAIM in the
debug_objects_fill_pool() case.
Since ___slab_alloc() has preemption disabled and thus was using
GFP_NOWAIT, we instead mask out __GFP_DIRECT_RECLAIM from the flags.
The oops looks something like:
BUG: spinlock recursion on CPU#3, swapper/3/0
lock: 0xffffff8a4bf29c80, .magic: dead4ead, .owner: swapper/3/0, .owner_cpu: 3
Hardware name: Qualcomm Technologies, Inc. Popsicle based on SM8850 (DT)
Call trace:
spin_bug+0x0
_raw_spin_lock_irqsave+0x80
hrtimer_try_to_cancel+0x94
task_contending+0x10c
enqueue_dl_entity+0x2a4
dl_server_start+0x74
enqueue_task_fair+0x568
enqueue_task+0xac
do_activate_task+0x14c
ttwu_do_activate+0xcc
try_to_wake_up+0x6c8
default_wake_function+0x20
autoremove_wake_function+0x1c
__wake_up+0xac
wakeup_kswapd+0x19c
wake_all_kswapds+0x78
__alloc_pages_slowpath+0x1ac
__alloc_pages_noprof+0x298
stack_depot_save_flags+0x6b0
stack_depot_save+0x14
set_track_prepare+0x5c
___slab_alloc+0xccc
__kmalloc_cache_noprof+0x470
__set_page_owner+0x2bc
post_alloc_hook[jt]+0x1b8
prep_new_page+0x28
get_page_from_freelist+0x1edc
__alloc_pages_noprof+0x13c
alloc_slab_page+0x244
allocate_slab+0x7c
___slab_alloc+0x8e8
kmem_cache_alloc_noprof+0x450
debug_objects_fill_pool+0x22c
debug_object_activate+0x40
enqueue_hrtimer[jt]+0xdc
hrtimer_start_range_ns+0x5f8
...
Signed-off-by: yangshiguang <yangshiguang@xiaomi.com>
Fixes: 5cf909c553e9 ("mm/slub: use stackdepot to save stack trace in objects")
Cc: stable@vger.kernel.org
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
diff --git a/mm/slub.c b/mm/slub.c
index 1787e4d51e48..d257141896c9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -962,19 +962,19 @@ static struct track *get_track(struct kmem_cache *s, void *object,
}
#ifdef CONFIG_STACKDEPOT
-static noinline depot_stack_handle_t set_track_prepare(void)
+static noinline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
{
depot_stack_handle_t handle;
unsigned long entries[TRACK_ADDRS_COUNT];
unsigned int nr_entries;
nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
- handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
+ handle = stack_depot_save(entries, nr_entries, gfp_flags);
return handle;
}
#else
-static inline depot_stack_handle_t set_track_prepare(void)
+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
{
return 0;
}
@@ -996,9 +996,9 @@ static void set_track_update(struct kmem_cache *s, void *object,
}
static __always_inline void set_track(struct kmem_cache *s, void *object,
- enum track_item alloc, unsigned long addr)
+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags)
{
- depot_stack_handle_t handle = set_track_prepare();
+ depot_stack_handle_t handle = set_track_prepare(gfp_flags);
set_track_update(s, object, alloc, addr, handle);
}
@@ -1926,9 +1926,9 @@ static inline bool free_debug_processing(struct kmem_cache *s,
static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
static inline int check_object(struct kmem_cache *s, struct slab *slab,
void *object, u8 val) { return 1; }
-static inline depot_stack_handle_t set_track_prepare(void) { return 0; }
+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }
static inline void set_track(struct kmem_cache *s, void *object,
- enum track_item alloc, unsigned long addr) {}
+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}
static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
struct slab *slab) {}
static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
@@ -3881,9 +3881,14 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
* For debug caches here we had to go through
* alloc_single_from_partial() so just store the
* tracking info and return the object.
+ *
+ * Due to disabled preemption we need to disallow
+ * blocking. The flags are further adjusted by
+ * gfp_nested_mask() in stack_depot itself.
*/
if (s->flags & SLAB_STORE_USER)
- set_track(s, freelist, TRACK_ALLOC, addr);
+ set_track(s, freelist, TRACK_ALLOC, addr,
+ gfpflags & ~(__GFP_DIRECT_RECLAIM));
return freelist;
}
@@ -3915,7 +3920,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
goto new_objects;
if (s->flags & SLAB_STORE_USER)
- set_track(s, freelist, TRACK_ALLOC, addr);
+ set_track(s, freelist, TRACK_ALLOC, addr,
+ gfpflags & ~(__GFP_DIRECT_RECLAIM));
return freelist;
}
@@ -4426,8 +4432,12 @@ static noinline void free_to_partial_list(
unsigned long flags;
depot_stack_handle_t handle = 0;
+ /*
+ * We cannot use GFP_NOWAIT as there are callsites where waking up
+ * kswapd could deadlock
+ */
if (s->flags & SLAB_STORE_USER)
- handle = set_track_prepare();
+ handle = set_track_prepare(__GFP_NOWARN);
spin_lock_irqsave(&n->list_lock, flags);
At 2025-09-01 16:46:13, "Vlastimil Babka" <vbabka@suse.cz> wrote:
>On 9/1/25 10:29, yangshiguang wrote:
>>
>>
>> At 2025-09-01 16:15:04, "Vlastimil Babka" <vbabka@suse.cz> wrote:
>>>On 9/1/25 09:50, David Rientjes wrote:
>>>> On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote:
>>>>
>>>>> From: yangshiguang <yangshiguang@xiaomi.com>
>>>>>
>>>>> From: yangshiguang <yangshiguang@xiaomi.com>
>>>>>
>>>>
>>>> Duplicate lines.
>>>>
>>>>> set_track_prepare() can incur lock recursion.
>>>>> The issue is that it is called from hrtimer_start_range_ns
>>>>> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
>>>>> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
>>>>> and try to hold the per_cpu(hrtimer_bases)[n].lock.
>>>>>
>>>>> Avoid deadlock caused by implicitly waking up kswapd by
>>>>> passing in allocation flags. And the slab caller context has
>>>>> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags.
>>>>>
>>>>
>>>> This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off
>>>> __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling
>>>> direct reclaim does not necessarily imply that kswapd will be disabled as
>>>> well.
>>>
>>>Yeah I think the changelog should say __GFP_DIRECT_RECLAIM.
>>>
>>>> Are you meaning to clear __GFP_RECLAIM in set_track_prepare()?
>>>
>>>No because if the context context (e.g. the hrtimers) can't support
>>>__GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to
>>
>>>set_track_prepare() so it already won't be there.
>>
>>
>> Sry. Should be __GFP_DIRECT_RECLAIM. I will resend the patch.
>
>I have adjusted it locally already. Also moved the masking of
>__GFP_DIRECT_RECLAIM to ___slab_alloc itself as that's where
>the preemption is disabled so it's more obvious.
>
>Does the result look good to you?
This looks good.
Currently only ___slab_alloc disables preemption context calls to set_track.
In the future, not all callers will disable preemption.
>
>commit 1b7052bc536650f8ca29b4f6f8682dc9f5692d16
>Author: yangshiguang <yangshiguang@xiaomi.com>
>Date: Sat Aug 30 10:09:46 2025 +0800
>
> mm: slub: avoid wake up kswapd in set_track_prepare
>
> set_track_prepare() can incur lock recursion.
> The issue is that it is called from hrtimer_start_range_ns
> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
> and try to hold the per_cpu(hrtimer_bases)[n].lock.
>
> Avoid deadlock caused by implicitly waking up kswapd by passing in
> allocation flags, which do not contain __GFP_KSWAPD_RECLAIM in the
> debug_objects_fill_pool() case.
> Since ___slab_alloc() has preemption disabled and thus was using
> GFP_NOWAIT, we instead mask out __GFP_DIRECT_RECLAIM from the flags.
>
> The oops looks something like:
>
> BUG: spinlock recursion on CPU#3, swapper/3/0
> lock: 0xffffff8a4bf29c80, .magic: dead4ead, .owner: swapper/3/0, .owner_cpu: 3
> Hardware name: Qualcomm Technologies, Inc. Popsicle based on SM8850 (DT)
> Call trace:
> spin_bug+0x0
> _raw_spin_lock_irqsave+0x80
> hrtimer_try_to_cancel+0x94
> task_contending+0x10c
> enqueue_dl_entity+0x2a4
> dl_server_start+0x74
> enqueue_task_fair+0x568
> enqueue_task+0xac
> do_activate_task+0x14c
> ttwu_do_activate+0xcc
> try_to_wake_up+0x6c8
> default_wake_function+0x20
> autoremove_wake_function+0x1c
> __wake_up+0xac
> wakeup_kswapd+0x19c
> wake_all_kswapds+0x78
> __alloc_pages_slowpath+0x1ac
> __alloc_pages_noprof+0x298
> stack_depot_save_flags+0x6b0
> stack_depot_save+0x14
> set_track_prepare+0x5c
> ___slab_alloc+0xccc
> __kmalloc_cache_noprof+0x470
> __set_page_owner+0x2bc
> post_alloc_hook[jt]+0x1b8
> prep_new_page+0x28
> get_page_from_freelist+0x1edc
> __alloc_pages_noprof+0x13c
> alloc_slab_page+0x244
> allocate_slab+0x7c
> ___slab_alloc+0x8e8
> kmem_cache_alloc_noprof+0x450
> debug_objects_fill_pool+0x22c
> debug_object_activate+0x40
> enqueue_hrtimer[jt]+0xdc
> hrtimer_start_range_ns+0x5f8
> ...
>
> Signed-off-by: yangshiguang <yangshiguang@xiaomi.com>
> Fixes: 5cf909c553e9 ("mm/slub: use stackdepot to save stack trace in objects")
> Cc: stable@vger.kernel.org
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>
>diff --git a/mm/slub.c b/mm/slub.c
>index 1787e4d51e48..d257141896c9 100644
>--- a/mm/slub.c
>+++ b/mm/slub.c
>@@ -962,19 +962,19 @@ static struct track *get_track(struct kmem_cache *s, void *object,
> }
>
> #ifdef CONFIG_STACKDEPOT
>-static noinline depot_stack_handle_t set_track_prepare(void)
>+static noinline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
> {
> depot_stack_handle_t handle;
> unsigned long entries[TRACK_ADDRS_COUNT];
> unsigned int nr_entries;
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
>- handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
>+ handle = stack_depot_save(entries, nr_entries, gfp_flags);
>
> return handle;
> }
> #else
>-static inline depot_stack_handle_t set_track_prepare(void)
>+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags)
> {
> return 0;
> }
>@@ -996,9 +996,9 @@ static void set_track_update(struct kmem_cache *s, void *object,
> }
>
> static __always_inline void set_track(struct kmem_cache *s, void *object,
>- enum track_item alloc, unsigned long addr)
>+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags)
> {
>- depot_stack_handle_t handle = set_track_prepare();
>+ depot_stack_handle_t handle = set_track_prepare(gfp_flags);
>
> set_track_update(s, object, alloc, addr, handle);
> }
>@@ -1926,9 +1926,9 @@ static inline bool free_debug_processing(struct kmem_cache *s,
> static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
> static inline int check_object(struct kmem_cache *s, struct slab *slab,
> void *object, u8 val) { return 1; }
>-static inline depot_stack_handle_t set_track_prepare(void) { return 0; }
>+static inline depot_stack_handle_t set_track_prepare(gfp_t gfp_flags) { return 0; }
> static inline void set_track(struct kmem_cache *s, void *object,
>- enum track_item alloc, unsigned long addr) {}
>+ enum track_item alloc, unsigned long addr, gfp_t gfp_flags) {}
> static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
> struct slab *slab) {}
> static inline void remove_full(struct kmem_cache *s, struct kmem_cache_node *n,
>@@ -3881,9 +3881,14 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> * For debug caches here we had to go through
> * alloc_single_from_partial() so just store the
> * tracking info and return the object.
>+ *
>+ * Due to disabled preemption we need to disallow
>+ * blocking. The flags are further adjusted by
>+ * gfp_nested_mask() in stack_depot itself.
> */
> if (s->flags & SLAB_STORE_USER)
>- set_track(s, freelist, TRACK_ALLOC, addr);
>+ set_track(s, freelist, TRACK_ALLOC, addr,
>+ gfpflags & ~(__GFP_DIRECT_RECLAIM));
>
> return freelist;
> }
>@@ -3915,7 +3920,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> goto new_objects;
>
> if (s->flags & SLAB_STORE_USER)
>- set_track(s, freelist, TRACK_ALLOC, addr);
>+ set_track(s, freelist, TRACK_ALLOC, addr,
>+ gfpflags & ~(__GFP_DIRECT_RECLAIM));
>
> return freelist;
> }
>@@ -4426,8 +4432,12 @@ static noinline void free_to_partial_list(
> unsigned long flags;
> depot_stack_handle_t handle = 0;
>
>+ /*
>+ * We cannot use GFP_NOWAIT as there are callsites where waking up
>+ * kswapd could deadlock
>+ */
> if (s->flags & SLAB_STORE_USER)
>- handle = set_track_prepare();
>+ handle = set_track_prepare(__GFP_NOWARN);
>
> spin_lock_irqsave(&n->list_lock, flags);
>
On 9/1/25 11:00, yangshiguang wrote: > > > At 2025-09-01 16:46:13, "Vlastimil Babka" <vbabka@suse.cz> wrote: >>On 9/1/25 10:29, yangshiguang wrote: >>> >>> >>> At 2025-09-01 16:15:04, "Vlastimil Babka" <vbabka@suse.cz> wrote: >>>>On 9/1/25 09:50, David Rientjes wrote: >>>>> On Sat, 30 Aug 2025, yangshiguang1011@163.com wrote: >>>>> >>>>>> From: yangshiguang <yangshiguang@xiaomi.com> >>>>>> >>>>>> From: yangshiguang <yangshiguang@xiaomi.com> >>>>>> >>>>> >>>>> Duplicate lines. >>>>> >>>>>> set_track_prepare() can incur lock recursion. >>>>>> The issue is that it is called from hrtimer_start_range_ns >>>>>> holding the per_cpu(hrtimer_bases)[n].lock, but when enabled >>>>>> CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare, >>>>>> and try to hold the per_cpu(hrtimer_bases)[n].lock. >>>>>> >>>>>> Avoid deadlock caused by implicitly waking up kswapd by >>>>>> passing in allocation flags. And the slab caller context has >>>>>> preemption disabled, so __GFP_KSWAPD_RECLAIM must not appear in gfp_flags. >>>>>> >>>>> >>>>> This mentions __GFP_KSWAPD_RECLAIM, but the patch actually masks off >>>>> __GFP_DIRECT_RECLAIM which would be a heavierweight operation. Disabling >>>>> direct reclaim does not necessarily imply that kswapd will be disabled as >>>>> well. >>>> >>>>Yeah I think the changelog should say __GFP_DIRECT_RECLAIM. >>>> >>>>> Are you meaning to clear __GFP_RECLAIM in set_track_prepare()? >>>> >>>>No because if the context context (e.g. the hrtimers) can't support >>>>__GFP_KSWAPD_RECLAIM it won't have it in gfp_flags and we now pass them to >>> >>>>set_track_prepare() so it already won't be there. >>> >>> >>> Sry. Should be __GFP_DIRECT_RECLAIM. I will resend the patch. >> >>I have adjusted it locally already. Also moved the masking of >>__GFP_DIRECT_RECLAIM to ___slab_alloc itself as that's where >>the preemption is disabled so it's more obvious. >> >>Does the result look good to you? > > This looks good. > Currently only ___slab_alloc disables preemption context calls to set_track. > In the future, not all callers will disable preemption. Great, added to slab/for-next-fixes. Thanks!
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