+ mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch added to mm-unstable branch

+ mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/slab: allow freeptr_offset to be used with ctor
has been added to the -mm mm-unstable branch.  Its filename is
     mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: mm/slab: allow freeptr_offset to be used with ctor
Date: Fri, 6 Dec 2024 14:52:02 -0800

There is no real reason to prevent freeptr_offset usage when a slab cache
has a ctor.  The only real limitation is that any field unioned with the
free pointer and initialized by ctor will be overwritten since free
pointer is set after @ctor invocation.  Document this limitation and
enable usage of freeptr_offset with ctor.

Link: https://lkml.kernel.org/r/20241206225204.4008261-6-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Sourav Panda <souravpanda@google.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/slab.h |    5 +++--
 mm/slub.c            |    2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

--- a/include/linux/slab.h~mm-slab-allow-freeptr_offset-to-be-used-with-ctor
+++ a/include/linux/slab.h
@@ -305,8 +305,9 @@ struct kmem_cache_args {
 	 * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset
 	 * is specified, %use_freeptr_offset must be set %true.
 	 *
-	 * Note that @ctor currently isn't supported with custom free pointers
-	 * as a @ctor requires an external free pointer.
+	 * Note that fields unioned with free pointer cannot be initialized by
+	 * @ctor since free pointer is set after @ctor invocation, so those
+	 * values will be overwritten.
 	 */
 	unsigned int freeptr_offset;
 	/**
--- a/mm/slub.c~mm-slab-allow-freeptr_offset-to-be-used-with-ctor
+++ a/mm/slub.c
@@ -5462,7 +5462,7 @@ static int calculate_sizes(struct kmem_c
 	s->inuse = size;
 
 	if (((flags & SLAB_TYPESAFE_BY_RCU) && !args->use_freeptr_offset) ||
-	    (flags & SLAB_POISON) || s->ctor ||
+	    (flags & SLAB_POISON) || (s->ctor && !args->use_freeptr_offset) ||
 	    ((flags & SLAB_RED_ZONE) &&
 	     (s->object_size < sizeof(void *) || slub_debug_orig_size(s)))) {
 		/*
_

Patches currently in -mm which might be from surenb@google.com are

alloc_tag-fix-module-allocation-tags-populated-area-calculation.patch
alloc_tag-fix-set_codetag_empty-when-config_mem_alloc_profiling_debug.patch
seqlock-add-raw_seqcount_try_begin.patch
mm-convert-mm_lock_seq-to-a-proper-seqcount.patch
mm-introduce-mmap_lock_speculate_try_beginretry.patch
mm-introduce-vma_start_read_locked_nested-helpers.patch
mm-move-per-vma-lock-into-vm_area_struct.patch
mm-mark-vma-as-detached-until-its-added-into-vma-tree.patch
mm-make-vma-cache-slab_typesafe_by_rcu.patch
mm-slab-allow-freeptr_offset-to-be-used-with-ctor.patch
docs-mm-document-latest-changes-to-vm_lock.patch