On Wed, Mar 02, 2022 at 06:31:17PM +0100, Vlastimil Babka wrote: > In a later patch we want to add stackdepot support for object owner > tracking in slub caches, which is enabled by slub_debug boot parameter. > This creates a bootstrap problem as some caches are created early in > boot when slab_is_available() is false and thus stack_depot_init() > tries to use memblock. But, as reported by Hyeonggon Yoo [1] we are > already beyond memblock_free_all(). Ideally memblock allocation should > fail, yet it succeeds, but later the system crashes, which is a > separately handled issue. > > To resolve this boostrap issue in a robust way, this patch adds another > way to request stack_depot_early_init(), which happens at a well-defined > point of time. In addition to build-time CONFIG_STACKDEPOT_ALWAYS_INIT, > code that's e.g. processing boot parmeters (which happens early enough) > can set a new variable stack_depot_want_early_init as true. > > In this patch we also convert page_owner to this approach. While it > doesn't have the bootstrap issue as slub, it's also a functionality > enabled by a boot param and can thus request stack_depot_early_init() > with memblock allocation instead of later initialization with > kvmalloc(). > > [1] https://lore.kernel.org/all/YhnUcqyeMgCrWZbd@xxxxxxxxxxxxxxxxxxx-northeast-1.compute.internal/ > > Reported-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > --- > include/linux/stackdepot.h | 16 ++++++++++++++-- > lib/stackdepot.c | 2 ++ > mm/page_owner.c | 9 ++++++--- > 3 files changed, 22 insertions(+), 5 deletions(-) > > diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h > index 17f992fe6355..1217ba2b636e 100644 > --- a/include/linux/stackdepot.h > +++ b/include/linux/stackdepot.h > @@ -15,6 +15,8 @@ > > typedef u32 depot_stack_handle_t; > > +extern bool stack_depot_want_early_init; > + > depot_stack_handle_t __stack_depot_save(unsigned long *entries, > unsigned int nr_entries, > gfp_t gfp_flags, bool can_alloc); > @@ -26,11 +28,21 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, > * The alternative is to select STACKDEPOT_ALWAYS_INIT to have stack depot > * enabled as part of mm_init(), for subsystems where it's known at compile time > * that stack depot will be used. > + * > + * Another alternative is to set stack_depot_want_early_init as true, when the > + * decision to use stack depot is taken e.g. when evaluating kernel boot > + * parameters, which precedes the call to stack_depot_want_early_init(). > */ > int stack_depot_init(void); > > -#ifdef CONFIG_STACKDEPOT_ALWAYS_INIT > -static inline int stack_depot_early_init(void) { return stack_depot_init(); } > +#ifdef CONFIG_STACKDEPOT > +static inline int stack_depot_early_init(void) > +{ > + if (IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT) > + || stack_depot_want_early_init) > + return stack_depot_init(); > + return 0; > +} I'd also suggest splitting memblock allocation from stack_depot_init() to stack_depot_early_init(). > #else > static inline int stack_depot_early_init(void) { return 0; } > #endif > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index bf5ba9af0500..02e2b5fcbf3b 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -66,6 +66,8 @@ struct stack_record { > unsigned long entries[]; /* Variable-sized array of entries. */ > }; > > +bool stack_depot_want_early_init = false; > + > static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; > > static int depot_index; > diff --git a/mm/page_owner.c b/mm/page_owner.c > index 99e360df9465..40dce2b81d13 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -42,7 +42,12 @@ static void init_early_allocated_pages(void); > > static int __init early_page_owner_param(char *buf) > { > - return kstrtobool(buf, &page_owner_enabled); > + int ret = kstrtobool(buf, &page_owner_enabled); > + > + if (page_owner_enabled) > + stack_depot_want_early_init = true; > + > + return ret; > } > early_param("page_owner", early_page_owner_param); > > @@ -80,8 +85,6 @@ static __init void init_page_owner(void) > if (!page_owner_enabled) > return; > > - stack_depot_init(); > - > register_dummy_stack(); > register_failure_stack(); > register_early_stack(); > -- > 2.35.1 > -- Sincerely yours, Mike.
