[PATCH 11/12] mm: make userland page table freeing RCU-safe
From: Lorenzo Stoakes (ARM)
Date: Tue Sep 01 2026 - 07:13:51 EST
Now every architecture has been converted to support
CONFIG_MMU_GATHER_RCU_TABLE_FREE, this configuration option no longer makes
any sense to keep around.
Therefore remove it, and remove all the dead code that existed for
!CONFIG_MMU_GATHER_RCU_TABLE_FREE architectures previously.
Additionally, CONFIG_MMU_GATHER_TABLE_FREE is no longer necessary, as all
architectures instead use CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE when a custom
__tlb_remove_table() is required, so remove this too.
A number of architectures only enabled CONFIG_MMU_GATHER_RCU_TABLE_FREE if
CONFIG_MMU was set, however the mmu_gather logic only actually does
something meaningful if CONFIG_MMU is set (mmu_gather.c is only compiled in
this case, for instance).
As a result, there's no need to gate any of this logic on CONFIG_MMU
explicitly.
CONFIG_PT_RECLAIM however does have a strict dependency on CONFIG_MMU, so
make this dependency explicit.
Additionally, correct comments to remove references to non-RCU page table
gathering and make it clear that this is not 'semi-RCU', nor has it been
since commit 1fb3d8c20bfa ("mm/mmu_gather: replace IPI with
synchronize_rcu() when batch allocation fails").
With this change in place the kernel policy is now that all page tables are
freed after an RCU grace period, and thus it is now safe to unconditionally
perform page table walks under RCU, safe in the knowledge that page tables
will not be freed underneath the walker.
This is all that is guaranteed, however, so naturally it is still incumbent
upon page table walkers to ensure that the page table entries are as
expected.
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
arch/Kconfig | 8 -----
arch/alpha/Kconfig | 1 -
arch/arc/Kconfig | 1 -
arch/arm/Kconfig | 1 -
arch/arm64/Kconfig | 1 -
arch/csky/Kconfig | 1 -
arch/hexagon/Kconfig | 1 -
arch/loongarch/Kconfig | 1 -
arch/m68k/Kconfig | 1 -
arch/microblaze/Kconfig | 1 -
arch/mips/Kconfig | 1 -
arch/nios2/Kconfig | 1 -
arch/openrisc/Kconfig | 1 -
arch/parisc/Kconfig | 1 -
arch/powerpc/Kconfig | 1 -
arch/riscv/Kconfig | 1 -
arch/s390/Kconfig | 1 -
arch/sh/Kconfig | 1 -
arch/sparc/Kconfig | 2 --
arch/sparc/include/asm/tlb_64.h | 2 --
arch/um/Kconfig | 1 -
arch/x86/Kconfig | 1 -
arch/xtensa/Kconfig | 1 -
include/asm-generic/tlb.h | 66 ++++++-----------------------------------
mm/Kconfig | 2 +-
mm/gup.c | 5 ++--
mm/mmu_gather.c | 30 ++++---------------
27 files changed, 18 insertions(+), 117 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 45c657772362..6f7516916797 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -526,13 +526,6 @@ config HAVE_ARCH_JUMP_LABEL
config HAVE_ARCH_JUMP_LABEL_RELATIVE
bool
-config MMU_GATHER_TABLE_FREE
- bool
-
-config MMU_GATHER_RCU_TABLE_FREE
- bool
- select MMU_GATHER_TABLE_FREE
-
config MMU_GATHER_PAGE_SIZE
bool
@@ -548,7 +541,6 @@ config MMU_GATHER_MERGE_VMAS
config MMU_GATHER_NO_GATHER
bool
- depends on MMU_GATHER_TABLE_FREE
config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
bool
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index e53ef2d88463..9063c7bda4e4 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -42,7 +42,6 @@ config ALPHA
select ARCH_STACKWALK
select CPU_NO_EFFICIENT_FFS if !ALPHA_EV67
select MMU_GATHER_NO_RANGE
- select MMU_GATHER_RCU_TABLE_FREE
select SPARSEMEM_EXTREME if SPARSEMEM
select ZONE_DMA
select TRACE_IRQFLAGS_SUPPORT
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 7a7542b61823..2ed7186c81c5 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -47,7 +47,6 @@ config ARC
select HAVE_SYSCALL_TRACEPOINTS
select IRQ_DOMAIN
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_RELA
select OF
select OF_EARLY_FLATTREE
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 72b9afc6ae10..0cc289a7184a 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -134,7 +134,6 @@ config ARM
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
- select MMU_GATHER_RCU_TABLE_FREE if MMU
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RSEQ
select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 2bbeded33da0..b6c2dd8b2612 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -221,7 +221,6 @@ config ARM64
select HAVE_RELIABLE_STACKTRACE
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_FUNCTION_ARG_ACCESS_API
- select MMU_GATHER_RCU_TABLE_FREE
select HAVE_RSEQ
select HAVE_RUST if RUSTC_SUPPORTS_ARM64
select HAVE_STACKPROTECTOR
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index 80f89ef1d962..4331313a42ff 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -96,7 +96,6 @@ config CSKY
select HAVE_SYSCALL_TRACEPOINTS
select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE
select MAY_HAVE_SPARSE_IRQ
select MODULES_USE_ELF_RELA if MODULES
select OF
diff --git a/arch/hexagon/Kconfig b/arch/hexagon/Kconfig
index d9b3fb86556b..b48491140013 100644
--- a/arch/hexagon/Kconfig
+++ b/arch/hexagon/Kconfig
@@ -23,7 +23,6 @@ config HEXAGON
# select HAVE_CLK
select GENERIC_ATOMIC64
select HAVE_PERF_EVENTS
- select MMU_GATHER_RCU_TABLE_FREE
# GENERIC_ALLOCATOR is used by dma_alloc_coherent()
select GENERIC_ALLOCATOR
select GENERIC_IRQ_PROBE
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 9c5def706222..d1b23da40737 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -188,7 +188,6 @@ config LOONGARCH
select IRQ_LOONGARCH_CPU
select LOCK_MM_AND_FIND_VMA
select MMU_GATHER_MERGE_VMAS if MMU
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_RELA if MODULES
select NEED_PER_CPU_EMBED_FIRST_CHUNK
select NEED_PER_CPU_PAGE_FIRST_CHUNK
diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index fa5d39549da9..eb84c3af92c0 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -37,7 +37,6 @@ config M68K
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_UID16
select MMU_GATHER_NO_RANGE if MMU
- select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_REL
select MODULES_USE_ELF_RELA
select NO_DMA if !MMU && !COLDFIRE
diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index af7e821e96c1..484ebb3baedf 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -41,7 +41,6 @@ config MICROBLAZE
select PCI_SYSCALL if PCI
select CPU_NO_EFFICIENT_FFS
select MMU_GATHER_NO_RANGE
- select MMU_GATHER_RCU_TABLE_FREE
select SPARSE_IRQ
select ZONE_DMA
select TRACE_IRQFLAGS_SUPPORT
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index e2eb9627bd14..f0c43d118ca0 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -97,7 +97,6 @@ config MIPS
select IRQ_FORCED_THREADING
select ISA if EISA
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_REL if MODULES
select MODULES_USE_ELF_RELA if MODULES && 64BIT
select PERF_USE_VMALLOC
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index b0ccfc3b7a7e..9c0e6eaeb005 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -19,7 +19,6 @@ config NIOS2
select HAVE_PAGE_SIZE_4KB
select IRQ_DOMAIN
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_RELA
select OF
select OF_EARLY_FLATTREE
diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index d90b24dd3bce..5eb995c13074 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -35,7 +35,6 @@ config OPENRISC
select GENERIC_ATOMIC64
select GENERIC_CLOCKEVENTS_BROADCAST
select GENERIC_SMP_IDLE_THREAD
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_RELA
select HAVE_DEBUG_STACKOVERFLOW
select OR1K_PIC
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index d3afac2f0d9b..77f67028ad89 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -80,7 +80,6 @@ config PARISC
select GENERIC_CLOCKEVENTS
select CPU_NO_EFFICIENT_FFS
select THREAD_INFO_IN_TASK
- select MMU_GATHER_RCU_TABLE_FREE
select NEED_DMA_MAP_STATE
select NEED_SG_DMA_LENGTH
select HAVE_ARCH_KGDB
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2580e27e4328..0767cfcbaa42 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -307,7 +307,6 @@ config PPC
select KASAN_VMALLOC if KASAN && EXECMEM
select LOCK_MM_AND_FIND_VMA
select MMU_GATHER_PAGE_SIZE
- select MMU_GATHER_RCU_TABLE_FREE
select HAVE_ARCH_TLB_REMOVE_TABLE
select MMU_GATHER_MERGE_VMAS
select MMU_LAZY_TLB_SHOOTDOWN if PPC_BOOK3S_64
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 3529ed1861ce..7741a4287498 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -208,7 +208,6 @@ config RISCV
select IRQ_FORCED_THREADING
select KASAN_VMALLOC if KASAN
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_RELA if MODULES
select OF
select OF_EARLY_FLATTREE
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index b88b85042136..a34376c05f6e 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -267,7 +267,6 @@ config S390
select LOCK_MM_AND_FIND_VMA
select MMU_GATHER_MERGE_VMAS
select MMU_GATHER_NO_GATHER
- select MMU_GATHER_RCU_TABLE_FREE
select MODULES_USE_ELF_RELA
select NEED_DMA_MAP_STATE if PCI
select NEED_PER_CPU_EMBED_FIRST_CHUNK
diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 75236bef6f16..fe859def918c 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -62,7 +62,6 @@ config SUPERH
select HAVE_SYSCALL_TRACEPOINTS
select IRQ_FORCED_THREADING
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_RELA
select NEED_SG_DMA_LENGTH
select NO_DMA if !MMU && !DMA_COHERENT
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 79c09d6ee466..742ffff8c37f 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -64,7 +64,6 @@ config SPARC32
select HAVE_UID16
select HAVE_PAGE_SIZE_4KB
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE
select HAVE_ARCH_TLB_REMOVE_TABLE
select OLD_SIGACTION
select ZONE_DMA
@@ -77,7 +76,6 @@ config SPARC64
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_KRETPROBES
select HAVE_KPROBES
- select MMU_GATHER_RCU_TABLE_FREE
select HAVE_ARCH_TLB_REMOVE_TABLE
select MMU_GATHER_MERGE_VMAS
select MMU_GATHER_NO_FLUSH_CACHE
diff --git a/arch/sparc/include/asm/tlb_64.h b/arch/sparc/include/asm/tlb_64.h
index 3037187482db..f5f9631685d5 100644
--- a/arch/sparc/include/asm/tlb_64.h
+++ b/arch/sparc/include/asm/tlb_64.h
@@ -29,9 +29,7 @@ void flush_tlb_pending(void);
* and therefore we don't need a TLBI when freeing page-table pages.
*/
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
#define tlb_needs_table_invalidate() (false)
-#endif
#include <asm-generic/tlb.h>
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index d9541d13d9eb..94b8ff70f578 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -44,7 +44,6 @@ config UML
select HAVE_SYSCALL_TRACEPOINTS
select THREAD_INFO_IN_TASK
select SPARSE_IRQ
- select MMU_GATHER_RCU_TABLE_FREE
config MMU
bool
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a8c3b3d31a27..6e5e462ec059 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -283,7 +283,6 @@ config X86
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
select ASYNC_KERNEL_PGTABLE_FREE if IOMMU_SVA
- select MMU_GATHER_RCU_TABLE_FREE
select MMU_GATHER_MERGE_VMAS
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 33c4caee30e2..f2f9cd9cde50 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -55,7 +55,6 @@ config XTENSA
select HAVE_VIRT_CPU_ACCOUNTING_GEN
select IRQ_DOMAIN
select LOCK_MM_AND_FIND_VMA
- select MMU_GATHER_RCU_TABLE_FREE if MMU
select MODULES_USE_ELF_RELA
select PERF_USE_VMALLOC
select TRACE_IRQFLAGS_SUPPORT
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index bdcc2778ac64..044dabc1fe9c 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -67,11 +67,8 @@
* - tlb_remove_table()
*
* tlb_remove_table() is the basic primitive to free page-table directories
- * (__p*_free_tlb()). In it's most primitive form it is an alias for
- * tlb_remove_page() below, for when page directories are pages and have no
- * additional constraints.
- *
- * See also MMU_GATHER_TABLE_FREE and MMU_GATHER_RCU_TABLE_FREE.
+ * (__p*_free_tlb()). Page directories are freed after an RCU grace
+ * period - see the comment in mm/mmu_gather.c.
*
* - tlb_remove_page() / tlb_remove_page_size()
* - __tlb_remove_folio_pages() / __tlb_remove_page_size()
@@ -151,24 +148,15 @@
* This might be useful if your architecture has size specific TLB
* invalidation instructions.
*
- * MMU_GATHER_TABLE_FREE
- *
- * This provides tlb_remove_table(), to be used instead of tlb_remove_page()
- * for page directores (__p*_free_tlb()).
- *
- * Useful if your architecture has non-page page directories.
+ * Page directories (__p*_free_tlb()) are always freed via tlb_remove_table(),
+ * after an RCU grace period (see mm/mmu_gather.c).
*
- * When used, an architecture is expected to provide __tlb_remove_table() or
- * use the generic __tlb_remove_table(), which does the actual freeing of these
- * pages.
+ * This serialises against software page-table walkers, including architectures
+ * which do not use IPIs for remote TLB invalidates.
*
- * MMU_GATHER_RCU_TABLE_FREE
- *
- * Like MMU_GATHER_TABLE_FREE, and adds semi-RCU semantics to the free (see
- * comment below).
- *
- * Useful if your architecture doesn't use IPIs for remote TLB invalidates
- * and therefore doesn't naturally serialize with software page-table walkers.
+ * An architecture is expected to provide __tlb_remove_table() (see
+ * HAVE_ARCH_TLB_REMOVE_TABLE) or use the generic __tlb_remove_table(), which
+ * does the actual freeing of these pages.
*
* MMU_GATHER_NO_FLUSH_CACHE
*
@@ -200,12 +188,8 @@
* various ptep_get_and_clear() functions.
*/
-#ifdef CONFIG_MMU_GATHER_TABLE_FREE
-
struct mmu_table_batch {
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
struct rcu_head rcu;
-#endif
unsigned int nr;
void *tables[];
};
@@ -224,23 +208,6 @@ static inline void __tlb_remove_table(void *table)
extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
-#else /* !CONFIG_MMU_GATHER_TABLE_FREE */
-
-static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page);
-/*
- * Without MMU_GATHER_TABLE_FREE the architecture is assumed to have page based
- * page directories and we can use the normal page batching to free them.
- */
-static inline void tlb_remove_table(struct mmu_gather *tlb, void *table)
-{
- struct ptdesc *ptdesc = (struct ptdesc *)table;
-
- pagetable_dtor(ptdesc);
- tlb_remove_page(tlb, ptdesc_page(ptdesc));
-}
-#endif /* CONFIG_MMU_GATHER_TABLE_FREE */
-
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
/*
* This allows an architecture that does not use the linux page-tables for
* hardware to skip the TLBI when freeing page tables.
@@ -253,19 +220,6 @@ void tlb_remove_table_sync_one(void);
void tlb_remove_table_sync_rcu(void);
-#else
-
-#ifdef tlb_needs_table_invalidate
-#error tlb_needs_table_invalidate() requires MMU_GATHER_RCU_TABLE_FREE
-#endif
-
-static inline void tlb_remove_table_sync_one(void) { }
-
-static inline void tlb_remove_table_sync_rcu(void) { }
-
-#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
-
-
#ifndef CONFIG_MMU_GATHER_NO_GATHER
/*
* If we can't allocate a page to make a big batch of page pointers
@@ -325,9 +279,7 @@ static inline void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct
struct mmu_gather {
struct mm_struct *mm;
-#ifdef CONFIG_MMU_GATHER_TABLE_FREE
struct mmu_table_batch *batch;
-#endif
unsigned long start;
unsigned long end;
diff --git a/mm/Kconfig b/mm/Kconfig
index c1ddf59c0d71..bc7befafb47b 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1465,7 +1465,7 @@ config HAVE_ARCH_TLB_REMOVE_TABLE
config PT_RECLAIM
def_bool y
- depends on MMU_GATHER_RCU_TABLE_FREE && !HAVE_ARCH_TLB_REMOVE_TABLE
+ depends on MMU && !HAVE_ARCH_TLB_REMOVE_TABLE
help
Try to reclaim empty user page table pages in paths other than munmap
and exit_mmap path.
diff --git a/mm/gup.c b/mm/gup.c
index eb898ea1ee22..63b435ec605c 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2700,8 +2700,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
* Before activating this code, please be aware that the following assumptions
* are currently made:
*
- * *) Either MMU_GATHER_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
- * free pages containing page tables or TLB flushing requires IPI broadcast.
+ * *) tlb_remove_table() is used to free pages containing page tables, with
+ * the free deferred until an RCU grace period has elapsed (see
+ * mm/mmu_gather.c).
*
* *) ptes can be read atomically by the architecture.
*
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 3985d856de7f..2a72a9686773 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -218,8 +218,6 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
#endif /* MMU_GATHER_NO_GATHER */
-#ifdef CONFIG_MMU_GATHER_TABLE_FREE
-
static void __tlb_remove_table_free(struct mmu_table_batch *batch)
{
int i;
@@ -230,10 +228,8 @@ static void __tlb_remove_table_free(struct mmu_table_batch *batch)
free_page((unsigned long)batch);
}
-#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
-
/*
- * Semi RCU freeing of the page directories.
+ * RCU freeing of the page directories.
*
* This is needed by some architectures to implement software pagetable walkers.
*
@@ -259,13 +255,13 @@ static void __tlb_remove_table_free(struct mmu_table_batch *batch)
* means.
*
* What we do is batch the freed directory pages (tables) and RCU free them.
- * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
- * holds off grace periods.
+ * Disabling IRQs or preemption holds off RCU grace periods, so this protects
+ * both rcu_read_lock() and IRQ-disabling walkers.
*
* However, in order to batch these pages we need to allocate storage, this
* allocation is deep inside the MM code and can thus easily fail on memory
- * pressure. To guarantee progress we fall back to single table freeing, see
- * the implementation of tlb_remove_table_one().
+ * pressure. To guarantee progress we fall back to single table freeing, which
+ * is also RCU-deferred - see the implementation of tlb_remove_table_one().
*
*/
@@ -315,15 +311,6 @@ void tlb_remove_table_sync_rcu(void)
synchronize_rcu();
}
-#else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
-
-static void tlb_remove_table_free(struct mmu_table_batch *batch)
-{
- __tlb_remove_table_free(batch);
-}
-
-#endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
-
/*
* If we want tlb_remove_table() to imply TLB invalidates.
*/
@@ -403,13 +390,6 @@ static inline void tlb_table_init(struct mmu_gather *tlb)
tlb->batch = NULL;
}
-#else /* !CONFIG_MMU_GATHER_TABLE_FREE */
-
-static inline void tlb_table_flush(struct mmu_gather *tlb) { }
-static inline void tlb_table_init(struct mmu_gather *tlb) { }
-
-#endif /* CONFIG_MMU_GATHER_TABLE_FREE */
-
static void tlb_flush_mmu_free(struct mmu_gather *tlb)
{
tlb_table_flush(tlb);
--
2.55.0