On Mon, Feb 28, 2022 at 05:28:17PM +0100, Marco Elver wrote:
> On Mon, Feb 28, 2022 at 03:09PM +0000, Hyeonggon Yoo wrote:
> > commit ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in
> > objects") initializes stack depot while creating cache if SLAB_STORE_USER
> > flag is set.
> >
> > This can make kernel crash because a cache can be created in various
> > contexts. For example if user sets slub_debug=U, kernel crashes
> > because create_boot_cache() calls stack_depot_init(), which tries to
> > allocate hash table using memblock_alloc() if slab is not available.
> > But memblock is also not available at that time.
> >
> > This patch solves the problem by initializing stack depot early
> > in boot process if SLAB_STORE_USER debug flag is set globally
> > or the flag is set to at least one cache.
> >
> > [ elver@xxxxxxxxxx: initialize stack depot depending on slub_debug
> > parameter instead of allowing stack_depot_init() can be called
> > in kmem_cache_init() for simplicity. ]
> >
> > Link: https://lkml.org/lkml/2022/2/28/238
>
> This would be a better permalink:
> https://lore.kernel.org/all/YhyeaP8lrzKgKm5A@xxxxxxxxxxxxxxxxxxx-northeast-1.compute.internal/
>
Agreed.
> > Fixes: ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in objects")
>
> This commit does not exist in -next.
>
It did not land -next yet.
> I assume you intend that "lib/stackdepot: Use page allocator if both
> slab and memblock is unavailable" should be dropped now.
>
I did not intend that, but I agree the patch you mentioned
should be dropped now.
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > ---
> > include/linux/slab.h | 1 +
> > init/main.c | 1 +
> > mm/slab.c | 4 ++++
> > mm/slob.c | 4 ++++
> > mm/slub.c | 28 +++++++++++++++++++++++++---
> > 5 files changed, 35 insertions(+), 3 deletions(-)
> [...]
> >
> > +/* Initialize stack depot if needed */
> > +void __init kmem_cache_init_early(void)
> > +{
> > +#ifdef CONFIG_STACKDEPOT
> > + slab_flags_t block_flags;
> > + char *next_block;
> > + char *slab_list;
> > +
> > + if (slub_debug & SLAB_STORE_USER)
> > + goto init_stack_depot;
> > +
> > + next_block = slub_debug_string;
> > + while (next_block) {
> > + next_block = parse_slub_debug_flags(next_block, &block_flags, &slab_list, false);
> > + if (block_flags & SLAB_STORE_USER)
> > + goto init_stack_depot;
> > + }
> > +
> > + return;
> > +
> > +init_stack_depot:
> > + stack_depot_init();
> > +#endif
> > +}
>
> You can simplify this function to avoid the goto:
>
> /* Initialize stack depot if needed */
> void __init kmem_cache_init_early(void)
> {
> #ifdef CONFIG_STACKDEPOT
> slab_flags_t flags = slub_debug;
> char *next_block = slub_debug_string;
> char *slab_list;
>
> for (;;) {
> if (flags & SLAB_STORE_USER) {
> stack_depot_init();
> break;
> }
> if (!next_block)
> break;
> next_block = parse_slub_debug_flags(next_block, &flags, &slab_list, false);
> }
> #endif
> }
>
> ^^ with this version, it'd also be much easier and less confusing to add
> other initialization logic unrelated to stackdepot later after the loop
> (should it ever be required).
Thank you for nice suggestion, but I want to try it in
setup_slub_debug() as Vlastimil said!
Thanks.
--
Thank you, You are awesome!
Hyeonggon :-)
