diff mbox series

[7/7] mm/slab: document kfree() as allowed for kmem_cache_alloc() objects

Message ID 20230310103210.22372-8-vbabka@suse.cz (mailing list archive)
State Not Applicable
Headers show
Series remove SLOB and allow kfree() with kmem_cache_alloc() | expand

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Context Check Description
netdev/tree_selection success Guessing tree name failed - patch did not apply

Commit Message

Vlastimil Babka March 10, 2023, 10:32 a.m. UTC
This will make it easier to free objects in situations when they can
come from either kmalloc() or kmem_cache_alloc(), and also allow
kfree_rcu() for freeing objects from kmem_cache_alloc().

For the SLAB and SLUB allocators this was always possible so with SLOB
gone, we can document it as supported.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
---
 Documentation/core-api/memory-allocation.rst | 15 +++++++++++----
 include/linux/rcupdate.h                     |  6 ++++--
 mm/slab_common.c                             |  5 +----
 3 files changed, 16 insertions(+), 10 deletions(-)

Comments

Mike Rapoport March 12, 2023, 9:59 a.m. UTC | #1
On Fri, Mar 10, 2023 at 11:32:09AM +0100, Vlastimil Babka wrote:
> This will make it easier to free objects in situations when they can
> come from either kmalloc() or kmem_cache_alloc(), and also allow
> kfree_rcu() for freeing objects from kmem_cache_alloc().
> 
> For the SLAB and SLUB allocators this was always possible so with SLOB
> gone, we can document it as supported.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> ---
>  Documentation/core-api/memory-allocation.rst | 15 +++++++++++----
>  include/linux/rcupdate.h                     |  6 ++++--
>  mm/slab_common.c                             |  5 +----
>  3 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
> index 5954ddf6ee13..f9e8d352ed67 100644
> --- a/Documentation/core-api/memory-allocation.rst
> +++ b/Documentation/core-api/memory-allocation.rst
> @@ -170,7 +170,14 @@ should be used if a part of the cache might be copied to the userspace.
>  After the cache is created kmem_cache_alloc() and its convenience
>  wrappers can allocate memory from that cache.
>  
> -When the allocated memory is no longer needed it must be freed. You can
> -use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and
> -`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And
> -don't forget to destroy the cache with kmem_cache_destroy().
> +When the allocated memory is no longer needed it must be freed. Objects

I'd add a line break before Objects                               ^

> +allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
> +Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
> +or also by `kfree` or `kvfree`, which can be more convenient as it does

Maybe replace 'or also by' with a coma:

Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`,
`kfree` or `kvfree`, which can be more convenient as it does


> +not require the kmem_cache pointed.

                             ^ pointer.

> +The rules for _bulk and _rcu flavors of freeing functions are analogical.

Maybe 

The same rules apply to _bulk and _rcu flavors of freeing functions.

> +
> +Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`.
> +Memory allocated by `kvmalloc` can be freed with `kvfree`.
> +Caches created by `kmem_cache_create` should be freed with
> +`kmem_cache_destroy` only after freeing all the allocated objects first.
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 094321c17e48..dcd2cf1e8326 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -976,8 +976,10 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
>   * either fall back to use of call_rcu() or rearrange the structure to
>   * position the rcu_head structure into the first 4096 bytes.
>   *
> - * Note that the allowable offset might decrease in the future, for example,
> - * to allow something like kmem_cache_free_rcu().
> + * The object to be freed can be allocated either by kmalloc() or
> + * kmem_cache_alloc().
> + *
> + * Note that the allowable offset might decrease in the future.
>   *
>   * The BUILD_BUG_ON check must not involve any function calls, hence the
>   * checks are done in macros here.
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 1522693295f5..607249785c07 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -989,12 +989,9 @@ EXPORT_SYMBOL(__kmalloc_node_track_caller);
>  
>  /**
>   * kfree - free previously allocated memory
> - * @object: pointer returned by kmalloc.
> + * @object: pointer returned by kmalloc() or kmem_cache_alloc()
>   *
>   * If @object is NULL, no operation is performed.
> - *
> - * Don't free memory not originally allocated by kmalloc()
> - * or you will run into trouble.
>   */
>  void kfree(const void *object)
>  {
> -- 
> 2.39.2
>
Vlastimil Babka March 15, 2023, 1:38 p.m. UTC | #2
On 3/12/23 10:59, Mike Rapoport wrote:
> On Fri, Mar 10, 2023 at 11:32:09AM +0100, Vlastimil Babka wrote:
>> This will make it easier to free objects in situations when they can
>> come from either kmalloc() or kmem_cache_alloc(), and also allow
>> kfree_rcu() for freeing objects from kmem_cache_alloc().
>> 
>> For the SLAB and SLUB allocators this was always possible so with SLOB
>> gone, we can document it as supported.
>> 
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Mike Rapoport <rppt@kernel.org>
>> Cc: Jonathan Corbet <corbet@lwn.net>
>> Cc: "Paul E. McKenney" <paulmck@kernel.org>
>> Cc: Frederic Weisbecker <frederic@kernel.org>
>> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
>> Cc: Josh Triplett <josh@joshtriplett.org>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
>> Cc: Joel Fernandes <joel@joelfernandes.org>
>> ---
>>  Documentation/core-api/memory-allocation.rst | 15 +++++++++++----
>>  include/linux/rcupdate.h                     |  6 ++++--
>>  mm/slab_common.c                             |  5 +----
>>  3 files changed, 16 insertions(+), 10 deletions(-)
>> 
>> diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
>> index 5954ddf6ee13..f9e8d352ed67 100644
>> --- a/Documentation/core-api/memory-allocation.rst
>> +++ b/Documentation/core-api/memory-allocation.rst
>> @@ -170,7 +170,14 @@ should be used if a part of the cache might be copied to the userspace.
>>  After the cache is created kmem_cache_alloc() and its convenience
>>  wrappers can allocate memory from that cache.
>>  
>> -When the allocated memory is no longer needed it must be freed. You can
>> -use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and
>> -`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And
>> -don't forget to destroy the cache with kmem_cache_destroy().
>> +When the allocated memory is no longer needed it must be freed. Objects
> 
> I'd add a line break before Objects                               ^
> 
>> +allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
>> +Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
>> +or also by `kfree` or `kvfree`, which can be more convenient as it does
> 
> Maybe replace 'or also by' with a coma:
> 
> Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`,
> `kfree` or `kvfree`, which can be more convenient as it does

But then I need to clarify what the "which" applies to?

> 
>> +not require the kmem_cache pointed.
> 
>                              ^ pointer.
> 
>> +The rules for _bulk and _rcu flavors of freeing functions are analogical.
> 
> Maybe 
> 
> The same rules apply to _bulk and _rcu flavors of freeing functions.

So like this incremental diff?

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index f9e8d352ed67..1c58d883b273 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -170,12 +170,14 @@ should be used if a part of the cache might be copied to the userspace.
 After the cache is created kmem_cache_alloc() and its convenience
 wrappers can allocate memory from that cache.
 
-When the allocated memory is no longer needed it must be freed. Objects
-allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
-Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
-or also by `kfree` or `kvfree`, which can be more convenient as it does
-not require the kmem_cache pointed.
-The rules for _bulk and _rcu flavors of freeing functions are analogical.
+When the allocated memory is no longer needed it must be freed.
+
+Objects allocated by `kmalloc` can be freed by `kfree` or `kvfree`. Objects
+allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`, `kfree`
+or `kvfree`, where the latter two might be more convenient thanks to not
+needing the kmem_cache pointer.
+
+The same rules apply to _bulk and _rcu flavors of freeing functions.
 
 Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`.
 Memory allocated by `kvmalloc` can be freed with `kvfree`.
Mike Rapoport March 15, 2023, 2:50 p.m. UTC | #3
On Wed, Mar 15, 2023 at 02:38:47PM +0100, Vlastimil Babka wrote:
> On 3/12/23 10:59, Mike Rapoport wrote:
> > On Fri, Mar 10, 2023 at 11:32:09AM +0100, Vlastimil Babka wrote:
> >> This will make it easier to free objects in situations when they can
> >> come from either kmalloc() or kmem_cache_alloc(), and also allow
> >> kfree_rcu() for freeing objects from kmem_cache_alloc().
> >> 
> >> For the SLAB and SLUB allocators this was always possible so with SLOB
> >> gone, we can document it as supported.
> >> 
> >> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> >> Cc: Mike Rapoport <rppt@kernel.org>
> >> Cc: Jonathan Corbet <corbet@lwn.net>
> >> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> >> Cc: Frederic Weisbecker <frederic@kernel.org>
> >> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> >> Cc: Josh Triplett <josh@joshtriplett.org>
> >> Cc: Steven Rostedt <rostedt@goodmis.org>
> >> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> >> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> >> Cc: Joel Fernandes <joel@joelfernandes.org>
> >> ---
> >>  Documentation/core-api/memory-allocation.rst | 15 +++++++++++----
> >>  include/linux/rcupdate.h                     |  6 ++++--
> >>  mm/slab_common.c                             |  5 +----
> >>  3 files changed, 16 insertions(+), 10 deletions(-)
> >> 
> >> diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
> >> index 5954ddf6ee13..f9e8d352ed67 100644
> >> --- a/Documentation/core-api/memory-allocation.rst
> >> +++ b/Documentation/core-api/memory-allocation.rst
> >> @@ -170,7 +170,14 @@ should be used if a part of the cache might be copied to the userspace.
> >>  After the cache is created kmem_cache_alloc() and its convenience
> >>  wrappers can allocate memory from that cache.
> >>  
> >> -When the allocated memory is no longer needed it must be freed. You can
> >> -use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and
> >> -`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And
> >> -don't forget to destroy the cache with kmem_cache_destroy().
> >> +When the allocated memory is no longer needed it must be freed. Objects
> > 
> > I'd add a line break before Objects                               ^
> > 
> >> +allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
> >> +Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
> >> +or also by `kfree` or `kvfree`, which can be more convenient as it does
> > 
> > Maybe replace 'or also by' with a coma:
> > 
> > Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`,
> > `kfree` or `kvfree`, which can be more convenient as it does
> 
> But then I need to clarify what the "which" applies to?

Yeah, I kinda missed that...

> > 
> >> +not require the kmem_cache pointed.
> > 
> >                              ^ pointer.
> > 
> >> +The rules for _bulk and _rcu flavors of freeing functions are analogical.
> > 
> > Maybe 
> > 
> > The same rules apply to _bulk and _rcu flavors of freeing functions.
> 
> So like this incremental diff?
 
> diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
> index f9e8d352ed67..1c58d883b273 100644
> --- a/Documentation/core-api/memory-allocation.rst
> +++ b/Documentation/core-api/memory-allocation.rst
> @@ -170,12 +170,14 @@ should be used if a part of the cache might be copied to the userspace.
>  After the cache is created kmem_cache_alloc() and its convenience
>  wrappers can allocate memory from that cache.
>  
> -When the allocated memory is no longer needed it must be freed. Objects
> -allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
> -Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
> -or also by `kfree` or `kvfree`, which can be more convenient as it does
> -not require the kmem_cache pointed.
> -The rules for _bulk and _rcu flavors of freeing functions are analogical.
> +When the allocated memory is no longer needed it must be freed.
> +
> +Objects allocated by `kmalloc` can be freed by `kfree` or `kvfree`. Objects
> +allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`, `kfree`
> +or `kvfree`, where the latter two might be more convenient thanks to not
> +needing the kmem_cache pointer.

... but this way it's more explicit that kfree and kvfree don't need
kmem_cache pointer.

> +
> +The same rules apply to _bulk and _rcu flavors of freeing functions.
>  
>  Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`.
>  Memory allocated by `kvmalloc` can be freed with `kvfree`.
>
diff mbox series

Patch

diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 5954ddf6ee13..f9e8d352ed67 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -170,7 +170,14 @@  should be used if a part of the cache might be copied to the userspace.
 After the cache is created kmem_cache_alloc() and its convenience
 wrappers can allocate memory from that cache.
 
-When the allocated memory is no longer needed it must be freed. You can
-use kvfree() for the memory allocated with `kmalloc`, `vmalloc` and
-`kvmalloc`. The slab caches should be freed with kmem_cache_free(). And
-don't forget to destroy the cache with kmem_cache_destroy().
+When the allocated memory is no longer needed it must be freed. Objects
+allocated by `kmalloc` can be freed by `kfree` or `kvfree`.
+Objects allocated by `kmem_cache_alloc` can be freed with `kmem_cache_free`
+or also by `kfree` or `kvfree`, which can be more convenient as it does
+not require the kmem_cache pointed.
+The rules for _bulk and _rcu flavors of freeing functions are analogical.
+
+Memory allocated by `vmalloc` can be freed with `vfree` or `kvfree`.
+Memory allocated by `kvmalloc` can be freed with `kvfree`.
+Caches created by `kmem_cache_create` should be freed with
+`kmem_cache_destroy` only after freeing all the allocated objects first.
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 094321c17e48..dcd2cf1e8326 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -976,8 +976,10 @@  static inline notrace void rcu_read_unlock_sched_notrace(void)
  * either fall back to use of call_rcu() or rearrange the structure to
  * position the rcu_head structure into the first 4096 bytes.
  *
- * Note that the allowable offset might decrease in the future, for example,
- * to allow something like kmem_cache_free_rcu().
+ * The object to be freed can be allocated either by kmalloc() or
+ * kmem_cache_alloc().
+ *
+ * Note that the allowable offset might decrease in the future.
  *
  * The BUILD_BUG_ON check must not involve any function calls, hence the
  * checks are done in macros here.
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1522693295f5..607249785c07 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -989,12 +989,9 @@  EXPORT_SYMBOL(__kmalloc_node_track_caller);
 
 /**
  * kfree - free previously allocated memory
- * @object: pointer returned by kmalloc.
+ * @object: pointer returned by kmalloc() or kmem_cache_alloc()
  *
  * If @object is NULL, no operation is performed.
- *
- * Don't free memory not originally allocated by kmalloc()
- * or you will run into trouble.
  */
 void kfree(const void *object)
 {