On 10/13/21 09:30, Vlastimil Babka wrote: > Currently, enabling CONFIG_STACKDEPOT means its stack_table will be allocated > from memblock, even if stack depot ends up not actually used. The default size > of stack_table is 4MB on 32-bit, 8MB on 64-bit. > > This is fine for use-cases such as KASAN which is also a config option and > has overhead on its own. But it's an issue for functionality that has to be > actually enabled on boot (page_owner) or depends on hardware (GPU drivers) > and thus the memory might be wasted. This was raised as an issue [1] when > attempting to add stackdepot support for SLUB's debug object tracking > functionality. It's common to build kernels with CONFIG_SLUB_DEBUG and enable > slub_debug on boot only when needed, or create only specific kmem caches with > debugging for testing purposes. > > It would thus be more efficient if stackdepot's table was allocated only when > actually going to be used. This patch thus makes the allocation (and whole > stack_depot_init() call) optional: > > - Add a CONFIG_STACKDEPOT_ALWAYS_INIT flag to keep using the current > well-defined point of allocation as part of mem_init(). Make CONFIG_KASAN > select this flag. > - Other users have to call stack_depot_init() as part of their own init when > it's determined that stack depot will actually be used. This may depend on > both config and runtime conditions. Convert current users which are > page_owner and several in the DRM subsystem. Same will be done for SLUB > later. > - Because the init might now be called after the boot-time memblock allocation > has given all memory to the buddy allocator, change stack_depot_init() to > allocate stack_table with kvmalloc() when memblock is no longer available. > Also handle allocation failure by disabling stackdepot (could have > theoretically happened even with memblock allocation previously), and don't > unnecessarily align the memblock allocation to its own size anymore. > > [1] https://lore.kernel.org/all/CAMuHMdW=eoVzM1Re5FVoEN87nKfiLmM2+Ah7eNu2KXEhCvbZyA@xxxxxxxxxxxxxx/ ... > --- > Changes in v3: > - stack_depot_init_mutex made static and moved inside stack_depot_init() > Reported-by: kernel test robot <lkp@xxxxxxxxx> > - use !stack_table condition instead of stack_table == NULL > reported by checkpatch on freedesktop.org patchwork The last change above was missing because I forgot git commit --amend before git format-patch. More importantly there was a bot report for FLATMEM. Please add this fixup. Thanks. ----8<---- >From a971a1670491f8fbbaab579eef3c756a5263af95 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka <vbabka@xxxxxxx> Date: Thu, 7 Oct 2021 10:49:09 +0200 Subject: [PATCH] lib/stackdepot: allow optional init and stack_table allocation by kvmalloc() - fixup On FLATMEM, we call page_ext_init_flatmem_late() just before kmem_cache_init() which means stack_depot_init() (called by page owner init) will not recognize properly it should use kvmalloc() and not memblock_alloc(). memblock_alloc() will also not issue a warning and return a block memory that can be invalid and cause kernel page fault when saving stacks, as reported by the kernel test robot [1]. Fix this by moving page_ext_init_flatmem_late() below kmem_cache_init() so that slab_is_available() is true during stack_depot_init(). SPARSEMEM doesn't have this issue, as it doesn't do page_ext_init_flatmem_late(), but a different page_ext_init() even later in the boot process. Thanks to Mike Rapoport for pointing out the FLATMEM init ordering issue. While at it, also actually resolve a checkpatch warning in stack_depot_init() from DRM CI, which was supposed to be in the original patch already. [1] https://lore.kernel.org/all/20211014085450.GC18719@xsang-OptiPlex-9020/ Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> --- init/main.c | 7 +++++-- lib/stackdepot.c | 2 +- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/init/main.c b/init/main.c index ca2765c8e45c..0ab632f681c5 100644 --- a/init/main.c +++ b/init/main.c @@ -845,9 +845,12 @@ static void __init mm_init(void) stack_depot_early_init(); mem_init(); mem_init_print_info(); - /* page_owner must be initialized after buddy is ready */ - page_ext_init_flatmem_late(); kmem_cache_init(); + /* + * page_owner must be initialized after buddy is ready, and also after + * slab is ready so that stack_depot_init() works properly + */ + page_ext_init_flatmem_late(); kmemleak_init(); pgtable_init(); debug_objects_mem_init(); diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 049d7d025d78..1f8ea6d0899b 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -172,7 +172,7 @@ __ref int stack_depot_init(void) static DEFINE_MUTEX(stack_depot_init_mutex); mutex_lock(&stack_depot_init_mutex); - if (!stack_depot_disable && stack_table == NULL) { + if (!stack_depot_disable && !stack_table) { size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); int i; -- 2.33.0
