[PATCH v2 02/21] mm/slab: remove CONFIG_SLAB from all Kconfig and Makefile

Vlastimil Babka
2023-11-20T18:34:41Z

Remove CONFIG_SLAB, CONFIG_DEBUG_SLAB, CONFIG_SLAB_DEPRECATED and
everything in Kconfig files and mm/Makefile that depends on those. Since
SLUB is the only remaining allocator, remove the allocator choice, make
CONFIG_SLUB a "def_bool y" for now and remove all explicit dependencies
on SLUB or SLAB as it's now always enabled. Make every option's verbose
name and description refer to "the slab allocator" without refering to
the specific implementation. Do not rename the CONFIG_ option names yet.

Everything under #ifdef CONFIG_SLAB, and mm/slab.c is now dead code, all
code under #ifdef CONFIG_SLUB is now always compiled.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
arch/arm64/Kconfig | 2 +-
arch/s390/Kconfig | 2 +-
arch/x86/Kconfig | 2 +-
lib/Kconfig.debug | 1 -
lib/Kconfig.kasan | 11 +++------
lib/Kconfig.kfence | 2 +-
lib/Kconfig.kmsan | 2 +-
mm/Kconfig | 68 ++++++++++++------------------------------------------
mm/Kconfig.debug | 16 ++++---------
mm/Makefile | 6 +----
10 files changed, 28 insertions(+), 84 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b071a00425d..325b7140b576 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -154,7 +154,7 @@ config ARM64
select HAVE_MOVE_PUD
select HAVE_PCI
select HAVE_ACPI_APEI if (ACPI && EFI)
- select HAVE_ALIGNED_STRUCT_PAGE if SLUB
+ select HAVE_ALIGNED_STRUCT_PAGE
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_BITREVERSE
select HAVE_ARCH_COMPILER_H
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 3bec98d20283..afa42a6f2e09 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -146,7 +146,7 @@ config S390
select GENERIC_TIME_VSYSCALL
select GENERIC_VDSO_TIME_NS
select GENERIC_IOREMAP if PCI
- select HAVE_ALIGNED_STRUCT_PAGE if SLUB
+ select HAVE_ALIGNED_STRUCT_PAGE
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_JUMP_LABEL_RELATIVE
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3762f41bb092..3f460f334d4e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -169,7 +169,7 @@ config X86
select HAS_IOPORT
select HAVE_ACPI_APEI if ACPI
select HAVE_ACPI_APEI_NMI if ACPI
- select HAVE_ALIGNED_STRUCT_PAGE if SLUB
+ select HAVE_ALIGNED_STRUCT_PAGE
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_HUGE_VMAP if X86_64 || X86_PAE
select HAVE_ARCH_HUGE_VMALLOC if X86_64
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cc7d53d9dc01..e1765face106 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1985,7 +1985,6 @@ config FAULT_INJECTION
config FAILSLAB
bool "Fault-injection capability for kmalloc"
depends on FAULT_INJECTION
- depends on SLAB || SLUB
help
Provide fault-injection capability for kmalloc.

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index fdca89c05745..97e1fdbb5910 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -37,7 +37,7 @@ menuconfig KASAN
(HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS)) && \
CC_HAS_WORKING_NOSANITIZE_ADDRESS) || \
HAVE_ARCH_KASAN_HW_TAGS
- depends on (SLUB && SYSFS && !SLUB_TINY) || (SLAB && !DEBUG_SLAB)
+ depends on SYSFS && !SLUB_TINY
select STACKDEPOT_ALWAYS_INIT
help
Enables KASAN (Kernel Address Sanitizer) - a dynamic memory safety
@@ -78,7 +78,7 @@ config KASAN_GENERIC
bool "Generic KASAN"
depends on HAVE_ARCH_KASAN && CC_HAS_KASAN_GENERIC
depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
- select SLUB_DEBUG if SLUB
+ select SLUB_DEBUG
select CONSTRUCTORS
help
Enables Generic KASAN.
@@ -89,13 +89,11 @@ config KASAN_GENERIC
overhead of ~50% for dynamic allocations.
The performance slowdown is ~x3.

- (Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
-
config KASAN_SW_TAGS
bool "Software Tag-Based KASAN"
depends on HAVE_ARCH_KASAN_SW_TAGS && CC_HAS_KASAN_SW_TAGS
depends on CC_HAS_WORKING_NOSANITIZE_ADDRESS
- select SLUB_DEBUG if SLUB
+ select SLUB_DEBUG
select CONSTRUCTORS
help
Enables Software Tag-Based KASAN.
@@ -110,12 +108,9 @@ config KASAN_SW_TAGS
May potentially introduce problems related to pointer casting and
comparison, as it embeds a tag into the top byte of each pointer.

- (Incompatible with CONFIG_DEBUG_SLAB: the kernel does not boot.)
-
config KASAN_HW_TAGS
bool "Hardware Tag-Based KASAN"
depends on HAVE_ARCH_KASAN_HW_TAGS
- depends on SLUB
help
Enables Hardware Tag-Based KASAN.

diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
index 459dda9ef619..6fbbebec683a 100644
--- a/lib/Kconfig.kfence
+++ b/lib/Kconfig.kfence
@@ -5,7 +5,7 @@ config HAVE_ARCH_KFENCE

menuconfig KFENCE
bool "KFENCE: low-overhead sampling-based memory safety error detector"
- depends on HAVE_ARCH_KFENCE && (SLAB || SLUB)
+ depends on HAVE_ARCH_KFENCE
select STACKTRACE
select IRQ_WORK
help
diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
index ef2c8f256c57..0541d7b079cc 100644
--- a/lib/Kconfig.kmsan
+++ b/lib/Kconfig.kmsan
@@ -11,7 +11,7 @@ config HAVE_KMSAN_COMPILER
config KMSAN
bool "KMSAN: detector of uninitialized values use"
depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
- depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
+ depends on DEBUG_KERNEL && !KASAN && !KCSAN
depends on !PREEMPT_RT
select STACKDEPOT
select STACKDEPOT_ALWAYS_INIT
diff --git a/mm/Kconfig b/mm/Kconfig
index 89971a894b60..4636870499bb 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -226,52 +226,17 @@ config ZSMALLOC_CHAIN_SIZE

For more information, see zsmalloc documentation.

-menu "SLAB allocator options"
-
-choice
- prompt "Choose SLAB allocator"
- default SLUB
- help
- This option allows to select a slab allocator.
-
-config SLAB_DEPRECATED
- bool "SLAB (DEPRECATED)"
- depends on !PREEMPT_RT
- help
- Deprecated and scheduled for removal in a few cycles. Replaced by
- SLUB.
-
- If you cannot migrate to SLUB, please contact linux-mm@kvack.org
- and the people listed in the SLAB ALLOCATOR section of MAINTAINERS
- file, explaining why.
-
- The regular slab allocator that is established and known to work
- well in all environments. It organizes cache hot objects in
- per cpu and per node queues.
+menu "Slab allocator options"

config SLUB
- bool "SLUB (Unqueued Allocator)"
- help
- SLUB is a slab allocator that minimizes cache line usage
- instead of managing queues of cached objects (SLAB approach).
- Per cpu caching is realized using slabs of objects instead
- of queues of objects. SLUB can use memory efficiently
- and has enhanced diagnostics. SLUB is the default choice for
- a slab allocator.
-
-endchoice
-
-config SLAB
- bool
- default y
- depends on SLAB_DEPRECATED
+ def_bool y

config SLUB_TINY
- bool "Configure SLUB for minimal memory footprint"
- depends on SLUB && EXPERT
+ bool "Configure for minimal memory footprint"
+ depends on EXPERT
select SLAB_MERGE_DEFAULT
help
- Configures the SLUB allocator in a way to achieve minimal memory
+ Configures the slab allocator in a way to achieve minimal memory
footprint, sacrificing scalability, debugging and other features.
This is intended only for the smallest system that had used the
SLOB allocator and is not recommended for systems with more than
@@ -282,7 +247,6 @@ config SLUB_TINY
config SLAB_MERGE_DEFAULT
bool "Allow slab caches to be merged"
default y
- depends on SLAB || SLUB
help
For reduced kernel memory fragmentation, slab caches can be
merged when they share the same size and other characteristics.
@@ -296,7 +260,7 @@ config SLAB_MERGE_DEFAULT

config SLAB_FREELIST_RANDOM
bool "Randomize slab freelist"
- depends on SLAB || (SLUB && !SLUB_TINY)
+ depends on !SLUB_TINY
help
Randomizes the freelist order used on creating new pages. This
security feature reduces the predictability of the kernel slab
@@ -304,21 +268,19 @@ config SLAB_FREELIST_RANDOM

config SLAB_FREELIST_HARDENED
bool "Harden slab freelist metadata"
- depends on SLAB || (SLUB && !SLUB_TINY)
+ depends on !SLUB_TINY
help
Many kernel heap attacks try to target slab cache metadata and
other infrastructure. This options makes minor performance
sacrifices to harden the kernel slab allocator against common
- freelist exploit methods. Some slab implementations have more
- sanity-checking than others. This option is most effective with
- CONFIG_SLUB.
+ freelist exploit methods.

config SLUB_STATS
default n
- bool "Enable SLUB performance statistics"
- depends on SLUB && SYSFS && !SLUB_TINY
+ bool "Enable performance statistics"
+ depends on SYSFS && !SLUB_TINY
help
- SLUB statistics are useful to debug SLUBs allocation behavior in
+ The statistics are useful to debug slab allocation behavior in
order find ways to optimize the allocator. This should never be
enabled for production use since keeping statistics slows down
the allocator by a few percentage points. The slabinfo command
@@ -328,8 +290,8 @@ config SLUB_STATS

config SLUB_CPU_PARTIAL
default y
- depends on SLUB && SMP && !SLUB_TINY
- bool "SLUB per cpu partial cache"
+ depends on SMP && !SLUB_TINY
+ bool "Enable per cpu partial caches"
help
Per cpu partial caches accelerate objects allocation and freeing
that is local to a processor at the price of more indeterminism
@@ -339,7 +301,7 @@ config SLUB_CPU_PARTIAL

config RANDOM_KMALLOC_CACHES
default n
- depends on SLUB && !SLUB_TINY
+ depends on !SLUB_TINY
bool "Randomize slab caches for normal kmalloc"
help
A hardening feature that creates multiple copies of slab caches for
@@ -354,7 +316,7 @@ config RANDOM_KMALLOC_CACHES
limited degree of memory and CPU overhead that relates to hardware and
system workload.

-endmenu # SLAB allocator options
+endmenu # Slab allocator options

config SHUFFLE_PAGE_ALLOCATOR
bool "Page allocator randomization"
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 018a5bd2f576..321ab379994f 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -45,18 +45,10 @@ config DEBUG_PAGEALLOC_ENABLE_DEFAULT
Enable debug page memory allocations by default? This value
can be overridden by debug_pagealloc=off|on.

-config DEBUG_SLAB
- bool "Debug slab memory allocations"
- depends on DEBUG_KERNEL && SLAB
- help
- Say Y here to have the kernel do limited verification on memory
- allocation as well as poisoning memory on free to catch use of freed
- memory. This can make kmalloc/kfree-intensive workloads much slower.
-
config SLUB_DEBUG
default y
bool "Enable SLUB debugging support" if EXPERT
- depends on SLUB && SYSFS && !SLUB_TINY
+ depends on SYSFS && !SLUB_TINY
select STACKDEPOT if STACKTRACE_SUPPORT
help
SLUB has extensive debug support features. Disabling these can
@@ -66,7 +58,7 @@ config SLUB_DEBUG

config SLUB_DEBUG_ON
bool "SLUB debugging on by default"
- depends on SLUB && SLUB_DEBUG
+ depends on SLUB_DEBUG
select STACKDEPOT_ALWAYS_INIT if STACKTRACE_SUPPORT
default n
help
@@ -231,8 +223,8 @@ config DEBUG_KMEMLEAK
allocations. See Documentation/dev-tools/kmemleak.rst for more
details.

- Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
- of finding leaks due to the slab objects poisoning.
+ Enabling SLUB_DEBUG may increase the chances of finding leaks
+ due to the slab objects poisoning.

In order to access the kmemleak file, debugfs needs to be
mounted (usually at /sys/kernel/debug).
diff --git a/mm/Makefile b/mm/Makefile
index 33873c8aedb3..e4b5b75aaec9 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -4,7 +4,6 @@
#

KASAN_SANITIZE_slab_common.o := n
-KASAN_SANITIZE_slab.o := n
KASAN_SANITIZE_slub.o := n
KCSAN_SANITIZE_kmemleak.o := n

@@ -12,7 +11,6 @@ KCSAN_SANITIZE_kmemleak.o := n
# the same word but accesses to different bits of that word. Re-enable KCSAN
# for these when we have more consensus on what to do about them.
KCSAN_SANITIZE_slab_common.o := n
-KCSAN_SANITIZE_slab.o := n
KCSAN_SANITIZE_slub.o := n
KCSAN_SANITIZE_page_alloc.o := n
# But enable explicit instrumentation for memory barriers.
@@ -22,7 +20,6 @@ KCSAN_INSTRUMENT_BARRIERS := y
# flaky coverage that is not a function of syscall inputs. E.g. slab is out of
# free pages, or a task is migrated between nodes.
KCOV_INSTRUMENT_slab_common.o := n
-KCOV_INSTRUMENT_slab.o := n
KCOV_INSTRUMENT_slub.o := n
KCOV_INSTRUMENT_page_alloc.o := n
KCOV_INSTRUMENT_debug-pagealloc.o := n
@@ -66,6 +63,7 @@ obj-y += page-alloc.o
obj-y += init-mm.o
obj-y += memblock.o
obj-y += $(memory-hotplug-y)
+obj-y += slub.o

ifdef CONFIG_MMU
obj-$(CONFIG_ADVISE_SYSCALLS) += madvise.o
@@ -82,8 +80,6 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
obj-$(CONFIG_KSM) += ksm.o
obj-$(CONFIG_PAGE_POISONING) += page_poison.o
-obj-$(CONFIG_SLAB) += slab.o
-obj-$(CONFIG_SLUB) += slub.o
obj-$(CONFIG_KASAN) += kasan/
obj-$(CONFIG_KFENCE) += kfence/
obj-$(CONFIG_KMSAN) += kmsan/

--
2.42.1