From 47504ee04b9241548ae2c28be7d0b01cff3b7aa6 Mon Sep 17 00:00:00 2001 From: Dennis Zhou Date: Fri, 16 Feb 2018 12:07:19 -0600 Subject: percpu: add __GFP_NORETRY semantics to the percpu balancing path 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 Suggested-by: Daniel Borkmann Reported-by: syzbot+adb03f3f0bb57ce3acda@syzkaller.appspotmail.com Acked-by: Christoph Lameter Signed-off-by: Tejun Heo --- mm/percpu-vm.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) (limited to 'mm/percpu-vm.c') diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c index 9158e5a81391..0af71eb2fff0 100644 --- 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_chunk *chunk, * @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 pcpu_chunk *chunk, * @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 pcpu_chunk *chunk, * 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 pcpu_chunk *chunk, 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_chunk *chunk, 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; -- cgit v1.2.3