On Tue, Apr 05, 2022 at 02:40:03PM -0700, David Rientjes wrote: > On Mon, 4 Apr 2022, 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 parameters (which happens early enough) > > can call a new function stack_depot_want_early_init(), which sets a flag > > that stack_depot_early_init() will check. > > > > 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(). > > > > As suggested by Mike, make stack_depot_early_init() only attempt > > memblock allocation and stack_depot_init() only attempt kvmalloc(). > > Also change the latter to kvcalloc(). In both cases we can lose the > > explicit array zeroing, which the allocations do already. > > > > As suggested by Marco, provide empty implementations of the init > > functions for !CONFIG_STACKDEPOT builds to simplify the callers. > > > > [1] https://lore.kernel.org/all/YhnUcqyeMgCrWZbd@xxxxxxxxxxxxxxxxxxx-northeast-1.compute.internal/ > > > > Reported-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > > Suggested-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > Suggested-by: Marco Elver <elver@xxxxxxxxxx> > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > > Reviewed-by: Marco Elver <elver@xxxxxxxxxx> > > Reviewed-and-tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> > > Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > --- > > include/linux/stackdepot.h | 26 ++++++++++++--- > > lib/stackdepot.c | 66 +++++++++++++++++++++++++------------- > > mm/page_owner.c | 9 ++++-- > > 3 files changed, 72 insertions(+), 29 deletions(-) > > > > diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h > > index 17f992fe6355..bc2797955de9 100644 > > --- a/include/linux/stackdepot.h > > +++ b/include/linux/stackdepot.h > > @@ -20,18 +20,36 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries, > > gfp_t gfp_flags, bool can_alloc); > > > > /* > > - * Every user of stack depot has to call this during its own init when it's > > - * decided that it will be calling stack_depot_save() later. > > + * Every user of stack depot has to call stack_depot_init() during its own init > > + * when it's decided that it will be calling stack_depot_save() later. This is > > + * recommended for e.g. modules initialized later in the boot process, when > > + * slab_is_available() is true. > > * > > * 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 call stack_depot_want_early_init(), when the > > + * decision to use stack depot is taken e.g. when evaluating kernel boot > > + * parameters, which precedes the enablement point in mm_init(). > > + * > > + * stack_depot_init() and stack_depot_want_early_init() can be called regardless > > + * of CONFIG_STACKDEPOT and are no-op when disabled. The actual save/fetch/print > > + * functions should only be called from code that makes sure CONFIG_STACKDEPOT > > + * is enabled. > > */ > > +#ifdef CONFIG_STACKDEPOT > > int stack_depot_init(void); > > > > -#ifdef CONFIG_STACKDEPOT_ALWAYS_INIT > > -static inline int stack_depot_early_init(void) { return stack_depot_init(); } > > +void __init stack_depot_want_early_init(void); > > + > > +/* This is supposed to be called only from mm_init() */ > > +int __init stack_depot_early_init(void); > > #else > > +static inline int stack_depot_init(void) { return 0; } > > + > > +static inline void stack_depot_want_early_init(void) { } > > + > > static inline int stack_depot_early_init(void) { return 0; } > > #endif > > > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > > index bf5ba9af0500..6c4644c9ed44 100644 > > --- a/lib/stackdepot.c > > +++ b/lib/stackdepot.c > > @@ -66,6 +66,9 @@ struct stack_record { > > unsigned long entries[]; /* Variable-sized array of entries. */ > > }; > > > > +static bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT); > > +static bool __stack_depot_early_init_passed __initdata; > > + > > static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; > > > > static int depot_index; > > @@ -162,38 +165,57 @@ static int __init is_stack_depot_disabled(char *str) > > } > > early_param("stack_depot_disable", is_stack_depot_disabled); > > > > -/* > > - * __ref because of memblock_alloc(), which will not be actually called after > > - * the __init code is gone, because at that point slab_is_available() is true > > - */ > > -__ref int stack_depot_init(void) > > +void __init stack_depot_want_early_init(void) > > +{ > > + /* Too late to request early init now */ > > + WARN_ON(__stack_depot_early_init_passed); > > + > > + __stack_depot_want_early_init = true; > > +} > > + > > +int __init stack_depot_early_init(void) > > +{ > > + size_t size; > > + > > + /* This is supposed to be called only once, from mm_init() */ > > + if (WARN_ON(__stack_depot_early_init_passed)) > > + return 0; > > + > > + __stack_depot_early_init_passed = true; > > + > > + if (!__stack_depot_want_early_init || stack_depot_disable) > > + return 0; > > + > > + pr_info("Stack Depot early init allocating hash table with memblock_alloc\n"); > > + size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); > > I think the kvcalloc() in the main init path is very unlikely to fail, but > perhaps this memblock_alloc() might? If so, a nit might be to include > this size as part of the printk. memblock_alloc() is even more unlikely to fail than kvcalloc() ;-) But printing the size won't hurt. > Either way: > > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> -- Sincerely yours, Mike.
