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Date: Fri, 10 Mar 2023 11:32:09 +0100 From: Vlastimil Babka <vbabka@...e.cz> To: Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Pekka Enberg <penberg@...nel.org> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>, Roman Gushchin <roman.gushchin@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, rcu@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, patches@...ts.linux.dev, netdev@...r.kernel.org, linux-doc@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Jonathan Corbet <corbet@....net>, "Paul E. McKenney" <paulmck@...nel.org>, Frederic Weisbecker <frederic@...nel.org>, Neeraj Upadhyay <quic_neeraju@...cinc.com>, Josh Triplett <josh@...htriplett.org>, Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Lai Jiangshan <jiangshanlai@...il.com>, Joel Fernandes <joel@...lfernandes.org> Subject: [PATCH 7/7] mm/slab: document kfree() as allowed for kmem_cache_alloc() objects 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@...e.cz> Cc: Mike Rapoport <rppt@...nel.org> Cc: Jonathan Corbet <corbet@....net> Cc: "Paul E. McKenney" <paulmck@...nel.org> Cc: Frederic Weisbecker <frederic@...nel.org> Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com> Cc: Josh Triplett <josh@...htriplett.org> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> Cc: Lai Jiangshan <jiangshanlai@...il.com> Cc: Joel Fernandes <joel@...lfernandes.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 +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) { -- 2.39.2
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