On 3/2/22 18:47, Marco Elver wrote: > On Wed, Mar 02, 2022 at 06:31PM +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. > > Agree, I think this is the best solution. Thanks. >> 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); > > I think for stack_depot_init() it might now be convenient to provide a > no-op version automatically if !STACKDEPOT, which would avoid > some 'if (.. && IS_ENABLED(CONFIG_STACKDEPOT))' in a later patch. > > Similarly, for stack_depot_want_early_init, where instead you could > simply provide stack_depot_want_early_init() as a function, which simply > sets a boolean __stack_depot_want_early_init. If !STACKDEPOT, it'll also > just be a no-op function. Yeah, makes sense. I guess I have patch 3/6 wrong now anyway as with !STACKDEPOT it should fail linking due to missing stack_depot_want_early_init... >> >> -#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; >> +} >> #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; >> + > > This can be __initdata, right? I initially thought so too, but in include/linux/init.h found * Don't forget to initialize data not at file scope, i.e. within a function, * as gcc otherwise puts the data into the bss section and not into the init * section. But maybe that's just outdated as everyone seems to init them at file scope. >> 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 >>
