This is a note to let you know that I've just added the patch titled

percpu: add __GFP_NORETRY semantics to the percpu balancing path

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: percpu-add-__gfp_noretry-semantics-to-the-percpu-balancing-path.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 47504ee04b9241548ae2c28be7d0b01cff3b7aa6 Mon Sep 17 00:00:00 2001

From: Dennis Zhou dennisszhou@gmail.com Date: Fri, 16 Feb 2018 12:07:19 -0600 Subject: percpu: add __GFP_NORETRY semantics to the percpu balancing path

From: Dennis Zhou dennisszhou@gmail.com

commit 47504ee04b9241548ae2c28be7d0b01cff3b7aa6 upstream.

Percpu memory using the vmalloc area based chunk allocator lazily populates chunks by first requesting the full virtual address space required for the chunk and subsequently adding pages as allocations come through. To ensure atomic allocations can succeed, a workqueue item is used to maintain a minimum number of empty pages. In certain scenarios, such as reported in [1], it is possible that physical memory becomes quite scarce which can result in either a rather long time spent trying to find free pages or worse, a kernel panic.

This patch adds support for __GFP_NORETRY and __GFP_NOWARN passing them through to the underlying allocators. This should prevent any unnecessary panics potentially caused by the workqueue item. The passing of gfp around is as additional flags rather than a full set of flags. The next patch will change these to caller passed semantics.

V2: Added const modifier to gfp flags in the balance path. Removed an extra whitespace.

[1] https://lkml.org/lkml/2018/2/12/551

Signed-off-by: Dennis Zhou dennisszhou@gmail.com Suggested-by: Daniel Borkmann daniel@iogearbox.net Reported-by: syzbot+adb03f3f0bb57ce3acda@syzkaller.appspotmail.com Acked-by: Christoph Lameter cl@linux.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- mm/percpu-km.c | 8 ++++---- mm/percpu-vm.c | 18 +++++++++++------- mm/percpu.c | 45 ++++++++++++++++++++++++++++----------------- 3 files changed, 43 insertions(+), 28 deletions(-)

--- a/mm/percpu-km.c +++ b/mm/percpu-km.c @@ -34,7 +34,7 @@ #include <linux/log2.h>

static int pcpu_populate_chunk(struct pcpu_chunk *chunk, - int page_start, int page_end) + int page_start, int page_end, gfp_t gfp) { return 0; } @@ -45,18 +45,18 @@ static void pcpu_depopulate_chunk(struct /* nada */ }

-static struct pcpu_chunk *pcpu_create_chunk(void) +static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp) { const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT; struct pcpu_chunk *chunk; struct page *pages; int i;

- chunk = pcpu_alloc_chunk(); + chunk = pcpu_alloc_chunk(gfp); if (!chunk) return NULL;

- pages = alloc_pages(GFP_KERNEL, order_base_2(nr_pages)); + pages = alloc_pages(gfp | GFP_KERNEL, order_base_2(nr_pages)); if (!pages) { pcpu_free_chunk(chunk); return NULL; --- a/mm/percpu-vm.c +++ b/mm/percpu-vm.c @@ -37,7 +37,7 @@ static struct page **pcpu_get_pages(void lockdep_assert_held(&pcpu_alloc_mutex);

if (!pages) - pages = pcpu_mem_zalloc(pages_size); + pages = pcpu_mem_zalloc(pages_size, 0); return pages; }

@@ -73,18 +73,21 @@ static void pcpu_free_pages(struct pcpu_ * @pages: array to put the allocated pages into, indexed by pcpu_page_idx() * @page_start: page index of the first page to be allocated * @page_end: page index of the last page to be allocated + 1 + * @gfp: allocation flags passed to the underlying allocator * * Allocate pages [@page_start,@page_end) into @pages for all units. * The allocation is for @chunk. Percpu core doesn't care about the * content of @pages and will pass it verbatim to pcpu_map_pages(). */ static int pcpu_alloc_pages(struct pcpu_chunk *chunk, - struct page **pages, int page_start, int page_end) + struct page **pages, int page_start, int page_end, + gfp_t gfp) { - const gfp_t gfp = GFP_KERNEL | __GFP_HIGHMEM; unsigned int cpu, tcpu; int i;

+ gfp |= GFP_KERNEL | __GFP_HIGHMEM; + for_each_possible_cpu(cpu) { for (i = page_start; i < page_end; i++) { struct page **pagep = &pages[pcpu_page_idx(cpu, i)]; @@ -262,6 +265,7 @@ static void pcpu_post_map_flush(struct p * @chunk: chunk of interest * @page_start: the start page * @page_end: the end page + * @gfp: allocation flags passed to the underlying memory allocator * * For each cpu, populate and map pages [@page_start,@page_end) into * @chunk. @@ -270,7 +274,7 @@ static void pcpu_post_map_flush(struct p * pcpu_alloc_mutex, does GFP_KERNEL allocation. */ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, - int page_start, int page_end) + int page_start, int page_end, gfp_t gfp) { struct page **pages;

@@ -278,7 +282,7 @@ static int pcpu_populate_chunk(struct pc if (!pages) return -ENOMEM;

- if (pcpu_alloc_pages(chunk, pages, page_start, page_end)) + if (pcpu_alloc_pages(chunk, pages, page_start, page_end, gfp)) return -ENOMEM;

if (pcpu_map_pages(chunk, pages, page_start, page_end)) { @@ -325,12 +329,12 @@ static void pcpu_depopulate_chunk(struct pcpu_free_pages(chunk, pages, page_start, page_end); }

-static struct pcpu_chunk *pcpu_create_chunk(void) +static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp) { struct pcpu_chunk *chunk; struct vm_struct **vms;

- chunk = pcpu_alloc_chunk(); + chunk = pcpu_alloc_chunk(gfp); if (!chunk) return NULL;

--- a/mm/percpu.c +++ b/mm/percpu.c @@ -447,10 +447,12 @@ static void pcpu_next_fit_region(struct /** * pcpu_mem_zalloc - allocate memory * @size: bytes to allocate + * @gfp: allocation flags * * Allocate @size bytes. If @size is smaller than PAGE_SIZE, - * kzalloc() is used; otherwise, vzalloc() is used. The returned - * memory is always zeroed. + * kzalloc() is used; otherwise, the equivalent of vzalloc() is used. + * This is to facilitate passing through whitelisted flags. The + * returned memory is always zeroed. * * CONTEXT: * Does GFP_KERNEL allocation. @@ -458,15 +460,16 @@ static void pcpu_next_fit_region(struct * RETURNS: * Pointer to the allocated area on success, NULL on failure. */ -static void *pcpu_mem_zalloc(size_t size) +static void *pcpu_mem_zalloc(size_t size, gfp_t gfp) { if (WARN_ON_ONCE(!slab_is_available())) return NULL;

if (size <= PAGE_SIZE) - return kzalloc(size, GFP_KERNEL); + return kzalloc(size, gfp | GFP_KERNEL); else - return vzalloc(size); + return __vmalloc(size, gfp | GFP_KERNEL | __GFP_ZERO, + PAGE_KERNEL); }

/** @@ -1154,12 +1157,12 @@ static struct pcpu_chunk * __init pcpu_a return chunk; }

-static struct pcpu_chunk *pcpu_alloc_chunk(void) +static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp) { struct pcpu_chunk *chunk; int region_bits;

- chunk = pcpu_mem_zalloc(pcpu_chunk_struct_size); + chunk = pcpu_mem_zalloc(pcpu_chunk_struct_size, gfp); if (!chunk) return NULL;

@@ -1168,17 +1171,17 @@ static struct pcpu_chunk *pcpu_alloc_chu region_bits = pcpu_chunk_map_bits(chunk);

chunk->alloc_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits) * - sizeof(chunk->alloc_map[0])); + sizeof(chunk->alloc_map[0]), gfp); if (!chunk->alloc_map) goto alloc_map_fail;

chunk->bound_map = pcpu_mem_zalloc(BITS_TO_LONGS(region_bits + 1) * - sizeof(chunk->bound_map[0])); + sizeof(chunk->bound_map[0]), gfp); if (!chunk->bound_map) goto bound_map_fail;

chunk->md_blocks = pcpu_mem_zalloc(pcpu_chunk_nr_blocks(chunk) * - sizeof(chunk->md_blocks[0])); + sizeof(chunk->md_blocks[0]), gfp); if (!chunk->md_blocks) goto md_blocks_fail;

@@ -1277,9 +1280,10 @@ static void pcpu_chunk_depopulated(struc * pcpu_addr_to_page - translate address to physical address * pcpu_verify_alloc_info - check alloc_info is acceptable during init */ -static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size); +static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size, + gfp_t gfp); static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size); -static struct pcpu_chunk *pcpu_create_chunk(void); +static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp); static void pcpu_destroy_chunk(struct pcpu_chunk *chunk); static struct page *pcpu_addr_to_page(void *addr); static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai); @@ -1421,7 +1425,7 @@ restart: }

if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) { - chunk = pcpu_create_chunk(); + chunk = pcpu_create_chunk(0); if (!chunk) { err = "failed to allocate new chunk"; goto fail; @@ -1450,7 +1454,7 @@ area_found: page_start, page_end) { WARN_ON(chunk->immutable);

- ret = pcpu_populate_chunk(chunk, rs, re); + ret = pcpu_populate_chunk(chunk, rs, re, 0);

spin_lock_irqsave(&pcpu_lock, flags); if (ret) { @@ -1561,10 +1565,17 @@ void __percpu *__alloc_reserved_percpu(s * pcpu_balance_workfn - manage the amount of free chunks and populated pages * @work: unused * - * Reclaim all fully free chunks except for the first one. + * Reclaim all fully free chunks except for the first one. This is also + * responsible for maintaining the pool of empty populated pages. However, + * it is possible that this is called when physical memory is scarce causing + * OOM killer to be triggered. We should avoid doing so until an actual + * allocation causes the failure as it is possible that requests can be + * serviced from already backed regions. */ static void pcpu_balance_workfn(struct work_struct *work) { + /* gfp flags passed to underlying allocators */ + const gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN; LIST_HEAD(to_free); struct list_head *free_head = &pcpu_slot[pcpu_nr_slots - 1]; struct pcpu_chunk *chunk, *next; @@ -1645,7 +1656,7 @@ retry_pop: chunk->nr_pages) { int nr = min(re - rs, nr_to_pop);

- ret = pcpu_populate_chunk(chunk, rs, rs + nr); + ret = pcpu_populate_chunk(chunk, rs, rs + nr, gfp); if (!ret) { nr_to_pop -= nr; spin_lock_irq(&pcpu_lock); @@ -1662,7 +1673,7 @@ retry_pop:

if (nr_to_pop) { /* ran out of chunks to populate, create a new one and retry */ - chunk = pcpu_create_chunk(); + chunk = pcpu_create_chunk(gfp); if (chunk) { spin_lock_irq(&pcpu_lock); pcpu_chunk_relocate(chunk, -1);

Patches currently in stable-queue which might be from dennisszhou@gmail.com are

queue-4.15/percpu-add-__gfp_noretry-semantics-to-the-percpu-balancing-path.patch