* [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false
@ 2025-09-12 10:25 kernel test robot
2025-09-12 13:23 ` Vlastimil Babka
0 siblings, 1 reply; 4+ messages in thread
From: kernel test robot @ 2025-09-12 10:25 UTC (permalink / raw)
To: Alexei Starovoitov; +Cc: llvm, oe-kbuild-all, linux-mm, Vlastimil Babka
tree: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git slab/for-6.18/kmalloc_nolock
head: 8014922e0e72dde7684abebeab3404720401679f
commit: 8014922e0e72dde7684abebeab3404720401679f [14/14] slab: Introduce kmalloc_nolock() and kfree_nolock().
config: x86_64-buildonly-randconfig-004-20250912 (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509121822.aOV6H1ts-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
3866 | local_lock_cpu_slab(s, flags);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
| ^~~~~~~~~~~
include/asm-generic/bug.h:171:25: note: expanded from macro 'WARN_ON'
171 | int __ret_warn_on = !!(condition); \
| ^~~~~~~~~
mm/slub.c:3891:27: note: uninitialized use occurs here
3891 | local_unlock_cpu_slab(s, flags);
| ^~~~~
mm/slub.c:3780:48: note: expanded from macro 'local_unlock_cpu_slab'
3780 | local_unlock_irqrestore(&(s)->cpu_slab->lock, flags)
| ^~~~~
include/linux/local_lock.h:52:48: note: expanded from macro 'local_unlock_irqrestore'
52 | __local_unlock_irqrestore(this_cpu_ptr(lock), flags)
| ^~~~~
include/linux/local_lock_internal.h:202:21: note: expanded from macro '__local_unlock_irqrestore'
202 | local_irq_restore(flags); \
| ^~~~~
include/linux/irqflags.h:240:61: note: expanded from macro 'local_irq_restore'
240 | #define local_irq_restore(flags) do { raw_local_irq_restore(flags); } while (0)
| ^~~~~
include/linux/irqflags.h:179:26: note: expanded from macro 'raw_local_irq_restore'
179 | arch_local_irq_restore(flags); \
| ^~~~~
mm/slub.c:3866:2: note: remove the '&&' if its condition is always true
3866 | local_lock_cpu_slab(s, flags);
| ^
mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
| ^
include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
| ^
mm/slub.c:3863:21: note: initialize the variable 'flags' to silence this warning
3863 | unsigned long flags;
| ^
| = 0
1 warning generated.
vim +3866 mm/slub.c
3852
3853 /*
3854 * Put a slab into a partial slab slot if available.
3855 *
3856 * If we did not find a slot then simply move all the partials to the
3857 * per node partial list.
3858 */
3859 static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain)
3860 {
3861 struct slab *oldslab;
3862 struct slab *slab_to_put = NULL;
3863 unsigned long flags;
3864 int slabs = 0;
3865
> 3866 local_lock_cpu_slab(s, flags);
3867
3868 oldslab = this_cpu_read(s->cpu_slab->partial);
3869
3870 if (oldslab) {
3871 if (drain && oldslab->slabs >= s->cpu_partial_slabs) {
3872 /*
3873 * Partial array is full. Move the existing set to the
3874 * per node partial list. Postpone the actual unfreezing
3875 * outside of the critical section.
3876 */
3877 slab_to_put = oldslab;
3878 oldslab = NULL;
3879 } else {
3880 slabs = oldslab->slabs;
3881 }
3882 }
3883
3884 slabs++;
3885
3886 slab->slabs = slabs;
3887 slab->next = oldslab;
3888
3889 this_cpu_write(s->cpu_slab->partial, slab);
3890
3891 local_unlock_cpu_slab(s, flags);
3892
3893 if (slab_to_put) {
3894 __put_partials(s, slab_to_put);
3895 stat(s, CPU_PARTIAL_DRAIN);
3896 }
3897 }
3898
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false
2025-09-12 10:25 [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false kernel test robot
@ 2025-09-12 13:23 ` Vlastimil Babka
2025-09-12 16:39 ` Alexei Starovoitov
0 siblings, 1 reply; 4+ messages in thread
From: Vlastimil Babka @ 2025-09-12 13:23 UTC (permalink / raw)
To: kernel test robot, Alexei Starovoitov, Harry Yoo
Cc: llvm, oe-kbuild-all, linux-mm
On 9/12/25 12:25, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git slab/for-6.18/kmalloc_nolock
> head: 8014922e0e72dde7684abebeab3404720401679f
> commit: 8014922e0e72dde7684abebeab3404720401679f [14/14] slab: Introduce kmalloc_nolock() and kfree_nolock().
> config: x86_64-buildonly-randconfig-004-20250912 (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202509121822.aOV6H1ts-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>>> mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
> 3866 | local_lock_cpu_slab(s, flags);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
> 3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
> 279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
> | ^~~~~~~~~~~
> include/asm-generic/bug.h:171:25: note: expanded from macro 'WARN_ON'
> 171 | int __ret_warn_on = !!(condition); \
> | ^~~~~~~~~
> mm/slub.c:3891:27: note: uninitialized use occurs here
> 3891 | local_unlock_cpu_slab(s, flags);
> | ^~~~~
> mm/slub.c:3780:48: note: expanded from macro 'local_unlock_cpu_slab'
> 3780 | local_unlock_irqrestore(&(s)->cpu_slab->lock, flags)
> | ^~~~~
> include/linux/local_lock.h:52:48: note: expanded from macro 'local_unlock_irqrestore'
> 52 | __local_unlock_irqrestore(this_cpu_ptr(lock), flags)
> | ^~~~~
> include/linux/local_lock_internal.h:202:21: note: expanded from macro '__local_unlock_irqrestore'
> 202 | local_irq_restore(flags); \
> | ^~~~~
> include/linux/irqflags.h:240:61: note: expanded from macro 'local_irq_restore'
> 240 | #define local_irq_restore(flags) do { raw_local_irq_restore(flags); } while (0)
> | ^~~~~
> include/linux/irqflags.h:179:26: note: expanded from macro 'raw_local_irq_restore'
> 179 | arch_local_irq_restore(flags); \
> | ^~~~~
> mm/slub.c:3866:2: note: remove the '&&' if its condition is always true
> 3866 | local_lock_cpu_slab(s, flags);
> | ^
> mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
> 3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
> | ^
> include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
> 279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
> | ^
> mm/slub.c:3863:21: note: initialize the variable 'flags' to silence this warning
> 3863 | unsigned long flags;
> | ^
> | = 0
> 1 warning generated.
>
>
> vim +3866 mm/slub.c
> 3852
> 3853 /*
> 3854 * Put a slab into a partial slab slot if available.
> 3855 *
> 3856 * If we did not find a slot then simply move all the partials to the
> 3857 * per node partial list.
> 3858 */
> 3859 static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain)
> 3860 {
> 3861 struct slab *oldslab;
> 3862 struct slab *slab_to_put = NULL;
> 3863 unsigned long flags;
> 3864 int slabs = 0;
> 3865
>> 3866 local_lock_cpu_slab(s, flags);
I guess this?
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3772,8 +3772,11 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
#define local_lock_cpu_slab(s, flags) \
local_lock_irqsave(&(s)->cpu_slab->lock, flags)
#else
-#define local_lock_cpu_slab(s, flags) \
- lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
+#define local_lock_cpu_slab(s, flags) \
+ do { \
+ bool __l = local_trylock_irqsave(&(s)->cpu_slab->lock, flags); \
+ lockdep_assert(__l); \
+ } while (0)
#endif
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false
2025-09-12 13:23 ` Vlastimil Babka
@ 2025-09-12 16:39 ` Alexei Starovoitov
2025-09-13 20:46 ` Vlastimil Babka
0 siblings, 1 reply; 4+ messages in thread
From: Alexei Starovoitov @ 2025-09-12 16:39 UTC (permalink / raw)
To: Vlastimil Babka
Cc: kernel test robot, Alexei Starovoitov, Harry Yoo,
clang-built-linux, oe-kbuild-all, linux-mm
On Fri, Sep 12, 2025 at 6:23 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 9/12/25 12:25, kernel test robot wrote:
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git slab/for-6.18/kmalloc_nolock
> > head: 8014922e0e72dde7684abebeab3404720401679f
> > commit: 8014922e0e72dde7684abebeab3404720401679f [14/14] slab: Introduce kmalloc_nolock() and kfree_nolock().
> > config: x86_64-buildonly-randconfig-004-20250912 (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/config)
> > compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250912/202509121822.aOV6H1ts-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202509121822.aOV6H1ts-lkp@intel.com/
> >
> > All warnings (new ones prefixed by >>):
> >
> >>> mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
> > 3866 | local_lock_cpu_slab(s, flags);
> > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
> > 3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
> > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
> > 279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
> > | ^~~~~~~~~~~
> > include/asm-generic/bug.h:171:25: note: expanded from macro 'WARN_ON'
> > 171 | int __ret_warn_on = !!(condition); \
> > | ^~~~~~~~~
> > mm/slub.c:3891:27: note: uninitialized use occurs here
> > 3891 | local_unlock_cpu_slab(s, flags);
> > | ^~~~~
> > mm/slub.c:3780:48: note: expanded from macro 'local_unlock_cpu_slab'
> > 3780 | local_unlock_irqrestore(&(s)->cpu_slab->lock, flags)
> > | ^~~~~
> > include/linux/local_lock.h:52:48: note: expanded from macro 'local_unlock_irqrestore'
> > 52 | __local_unlock_irqrestore(this_cpu_ptr(lock), flags)
> > | ^~~~~
> > include/linux/local_lock_internal.h:202:21: note: expanded from macro '__local_unlock_irqrestore'
> > 202 | local_irq_restore(flags); \
> > | ^~~~~
> > include/linux/irqflags.h:240:61: note: expanded from macro 'local_irq_restore'
> > 240 | #define local_irq_restore(flags) do { raw_local_irq_restore(flags); } while (0)
> > | ^~~~~
> > include/linux/irqflags.h:179:26: note: expanded from macro 'raw_local_irq_restore'
> > 179 | arch_local_irq_restore(flags); \
> > | ^~~~~
> > mm/slub.c:3866:2: note: remove the '&&' if its condition is always true
> > 3866 | local_lock_cpu_slab(s, flags);
> > | ^
> > mm/slub.c:3776:2: note: expanded from macro 'local_lock_cpu_slab'
> > 3776 | lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
> > | ^
> > include/linux/lockdep.h:279:15: note: expanded from macro 'lockdep_assert'
> > 279 | do { WARN_ON(debug_locks && !(cond)); } while (0)
> > | ^
> > mm/slub.c:3863:21: note: initialize the variable 'flags' to silence this warning
> > 3863 | unsigned long flags;
> > | ^
> > | = 0
> > 1 warning generated.
> >
> >
> > vim +3866 mm/slub.c
>
> > 3852
> > 3853 /*
> > 3854 * Put a slab into a partial slab slot if available.
> > 3855 *
> > 3856 * If we did not find a slot then simply move all the partials to the
> > 3857 * per node partial list.
> > 3858 */
> > 3859 static void put_cpu_partial(struct kmem_cache *s, struct slab *slab, int drain)
> > 3860 {
> > 3861 struct slab *oldslab;
> > 3862 struct slab *slab_to_put = NULL;
> > 3863 unsigned long flags;
> > 3864 int slabs = 0;
> > 3865
> >> 3866 local_lock_cpu_slab(s, flags);
>
> I guess this?
>
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3772,8 +3772,11 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
> #define local_lock_cpu_slab(s, flags) \
> local_lock_irqsave(&(s)->cpu_slab->lock, flags)
> #else
> -#define local_lock_cpu_slab(s, flags) \
> - lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
> +#define gg(s, flags) \
> + do { \
> + bool __l = local_trylock_irqsave(&(s)->cpu_slab->lock, flags); \
> + lockdep_assert(__l);
That works, but would raise questions for anyone looking at
these two lines as-is, since it's an implementation
detail of lockdep_assert() and combination of .config flags.
what clang warning suggested is imo cleaner:
diff --git a/mm/slub.c b/mm/slub.c
index 4079abb5d0e1..a6b50cd1d95f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3865,7 +3865,7 @@ static void put_cpu_partial(struct kmem_cache
*s, struct slab *slab, int drain)
{
struct slab *oldslab;
struct slab *slab_to_put = NULL;
- unsigned long flags;
+ unsigned long flags = 0;
int slabs = 0;
Could you fold one of them in?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false
2025-09-12 16:39 ` Alexei Starovoitov
@ 2025-09-13 20:46 ` Vlastimil Babka
0 siblings, 0 replies; 4+ messages in thread
From: Vlastimil Babka @ 2025-09-13 20:46 UTC (permalink / raw)
To: Alexei Starovoitov
Cc: kernel test robot, Alexei Starovoitov, Harry Yoo,
clang-built-linux, oe-kbuild-all, linux-mm
On 9/12/25 18:39, Alexei Starovoitov wrote:
> On Fri, Sep 12, 2025 at 6:23 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>>
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -3772,8 +3772,11 @@ static void deactivate_slab(struct kmem_cache *s, struct slab *slab,
>> #define local_lock_cpu_slab(s, flags) \
>> local_lock_irqsave(&(s)->cpu_slab->lock, flags)
>> #else
>> -#define local_lock_cpu_slab(s, flags) \
>> - lockdep_assert(local_trylock_irqsave(&(s)->cpu_slab->lock, flags))
>> +#define gg(s, flags) \
>> + do { \
>> + bool __l = local_trylock_irqsave(&(s)->cpu_slab->lock, flags); \
>> + lockdep_assert(__l);
>
> That works, but would raise questions for anyone looking at
> these two lines as-is, since it's an implementation
> detail of lockdep_assert() and combination of .config flags.
TBH when I see some code with a side-effect wrapped in a WARN or assert that
can be configured off, it already raises a question if that gets executed
when configured off. There are examples where it does, and where it doesn't.
> what clang warning suggested is imo cleaner:
That silences the warning about flags, however it means that when lockdep
gets disabled on runtime, the locks stop locking (but not unlocking). While
debug_locks_off() only seems to get called in a serious situations
currently, we should not make things even worse then.
> diff --git a/mm/slub.c b/mm/slub.c
> index 4079abb5d0e1..a6b50cd1d95f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3865,7 +3865,7 @@ static void put_cpu_partial(struct kmem_cache
> *s, struct slab *slab, int drain)
> {
> struct slab *oldslab;
> struct slab *slab_to_put = NULL;
> - unsigned long flags;
> + unsigned long flags = 0;
> int slabs = 0;
>
> Could you fold one of them in?
And so I've folded in mine.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2025-09-12 10:25 [vbabka-slab:slab/for-6.18/kmalloc_nolock 14/14] mm/slub.c:3866:2: warning: variable 'flags' is used uninitialized whenever '&&' condition is false kernel test robot
2025-09-12 13:23 ` Vlastimil Babka
2025-09-12 16:39 ` Alexei Starovoitov
2025-09-13 20:46 ` Vlastimil Babka
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