On Tue, 23 Jan 2024 at 16:53, Marco Elver <elver@xxxxxxxxxx> wrote: > > And on top of this we can make KASAN generic happier again: > > Objections? Not doing refcounting/aux locking for generic KASAN makes sense to me. > ------ >8 ------ > > From: Marco Elver <elver@xxxxxxxxxx> > Date: Tue, 23 Jan 2024 12:11:36 +0100 > Subject: [PATCH RFC] kasan: revert eviction of stack traces in generic mode > > This partially reverts commits cc478e0b6bdf, 63b85ac56a64, 08d7c94d9635, > a414d4286f34, and 773688a6cb24 to make use of variable-sized stack depot > records, since eviction of stack entries from stack depot forces fixed- > sized stack records. Care was taken to retain the code cleanups by the > above commits. > > Eviction was added to generic KASAN as a response to alleviating the > additional memory usage from fixed-sized stack records, but this still > uses more memory than previously. > > With the re-introduction of variable-sized records for stack depot, we > can just switch back to non-evictable stack records again, and return > back to the previous performance and memory usage baseline. > > Before (observed after a KASAN kernel boot): > > pools: 597 > allocations: 29657 > frees: 6425 > in_use: 23232 > freelist_size: 3493 > > After: > > pools: 315 > allocations: 28964 > frees: 0 > in_use: 28964 > freelist_size: 0 > > As can be seen from the number of "frees", with a generic KASAN config, > evictions are no longer used but due to using variable-sized records, I > observe a reduction of 282 stack depot pools (saving 4512 KiB). > > Fixes: cc478e0b6bdf ("kasan: avoid resetting aux_lock") > Fixes: 63b85ac56a64 ("kasan: stop leaking stack trace handles") > Fixes: 08d7c94d9635 ("kasan: memset free track in qlink_free") > Fixes: a414d4286f34 ("kasan: handle concurrent kasan_record_aux_stack calls") > Fixes: 773688a6cb24 ("kasan: use stack_depot_put for Generic mode") > Signed-off-by: Marco Elver <elver@xxxxxxxxxx> > Cc: Alexander Potapenko <glider@xxxxxxxxxx> > Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > --- > mm/kasan/common.c | 3 +-- > mm/kasan/generic.c | 54 ++++++---------------------------------------- > mm/kasan/kasan.h | 8 ------- > 3 files changed, 8 insertions(+), 57 deletions(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 610efae91220..ad32803e34e9 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -65,8 +65,7 @@ void kasan_save_track(struct kasan_track *track, gfp_t flags) > { > depot_stack_handle_t stack; > > - stack = kasan_save_stack(flags, > - STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET); > + stack = kasan_save_stack(flags, STACK_DEPOT_FLAG_CAN_ALLOC); > kasan_set_track(track, stack); > } > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > index df6627f62402..8bfb52b28c22 100644 > --- a/mm/kasan/generic.c > +++ b/mm/kasan/generic.c > @@ -485,16 +485,6 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object) > if (alloc_meta) { > /* Zero out alloc meta to mark it as invalid. */ > __memset(alloc_meta, 0, sizeof(*alloc_meta)); > - > - /* > - * Prepare the lock for saving auxiliary stack traces. > - * Temporarily disable KASAN bug reporting to allow instrumented > - * raw_spin_lock_init to access aux_lock, which resides inside > - * of a redzone. > - */ > - kasan_disable_current(); > - raw_spin_lock_init(&alloc_meta->aux_lock); > - kasan_enable_current(); > } > > /* > @@ -506,18 +496,8 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object) > > static void release_alloc_meta(struct kasan_alloc_meta *meta) > { > - /* Evict the stack traces from stack depot. */ > - stack_depot_put(meta->alloc_track.stack); > - stack_depot_put(meta->aux_stack[0]); > - stack_depot_put(meta->aux_stack[1]); > - > - /* > - * Zero out alloc meta to mark it as invalid but keep aux_lock > - * initialized to avoid having to reinitialize it when another object > - * is allocated in the same slot. > - */ > - __memset(&meta->alloc_track, 0, sizeof(meta->alloc_track)); > - __memset(meta->aux_stack, 0, sizeof(meta->aux_stack)); > + /* Zero out alloc meta to mark it as invalid. */ > + __memset(meta, 0, sizeof(*meta)); > } > > static void release_free_meta(const void *object, struct kasan_free_meta *meta) > @@ -526,9 +506,6 @@ static void release_free_meta(const void *object, struct kasan_free_meta *meta) > if (*(u8 *)kasan_mem_to_shadow(object) != KASAN_SLAB_FREE_META) > return; > > - /* Evict the stack trace from the stack depot. */ > - stack_depot_put(meta->free_track.stack); > - > /* Mark free meta as invalid. */ > *(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE; > } > @@ -571,8 +548,6 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags) > struct kmem_cache *cache; > struct kasan_alloc_meta *alloc_meta; > void *object; > - depot_stack_handle_t new_handle, old_handle; > - unsigned long flags; > > if (is_kfence_address(addr) || !slab) > return; > @@ -583,33 +558,18 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags) > if (!alloc_meta) > return; > > - new_handle = kasan_save_stack(0, depot_flags); > - > - /* > - * Temporarily disable KASAN bug reporting to allow instrumented > - * spinlock functions to access aux_lock, which resides inside of a > - * redzone. > - */ > - kasan_disable_current(); > - raw_spin_lock_irqsave(&alloc_meta->aux_lock, flags); > - old_handle = alloc_meta->aux_stack[1]; > alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0]; > - alloc_meta->aux_stack[0] = new_handle; > - raw_spin_unlock_irqrestore(&alloc_meta->aux_lock, flags); > - kasan_enable_current(); > - > - stack_depot_put(old_handle); > + alloc_meta->aux_stack[0] = kasan_save_stack(0, depot_flags); > } > > void kasan_record_aux_stack(void *addr) > { > - return __kasan_record_aux_stack(addr, > - STACK_DEPOT_FLAG_CAN_ALLOC | STACK_DEPOT_FLAG_GET); > + return __kasan_record_aux_stack(addr, STACK_DEPOT_FLAG_CAN_ALLOC); > } > > void kasan_record_aux_stack_noalloc(void *addr) > { > - return __kasan_record_aux_stack(addr, STACK_DEPOT_FLAG_GET); > + return __kasan_record_aux_stack(addr, 0); > } > > void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags) > @@ -620,7 +580,7 @@ void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags) > if (!alloc_meta) > return; > > - /* Evict previous stack traces (might exist for krealloc or mempool). */ > + /* Invalidate previous stack traces (might exist for krealloc or mempool). */ > release_alloc_meta(alloc_meta); > > kasan_save_track(&alloc_meta->alloc_track, flags); > @@ -634,7 +594,7 @@ void kasan_save_free_info(struct kmem_cache *cache, void *object) > if (!free_meta) > return; > > - /* Evict previous stack trace (might exist for mempool). */ > + /* Invalidate previous stack trace (might exist for mempool). */ > release_free_meta(object, free_meta); > > kasan_save_track(&free_meta->free_track, 0); > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > index d0f172f2b978..216ae0ef1e4b 100644 > --- a/mm/kasan/kasan.h > +++ b/mm/kasan/kasan.h > @@ -6,7 +6,6 @@ > #include <linux/kasan.h> > #include <linux/kasan-tags.h> > #include <linux/kfence.h> > -#include <linux/spinlock.h> > #include <linux/stackdepot.h> > > #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS) > @@ -265,13 +264,6 @@ struct kasan_global { > struct kasan_alloc_meta { > struct kasan_track alloc_track; > /* Free track is stored in kasan_free_meta. */ > - /* > - * aux_lock protects aux_stack from accesses from concurrent > - * kasan_record_aux_stack calls. It is a raw spinlock to avoid sleeping > - * on RT kernels, as kasan_record_aux_stack_noalloc can be called from > - * non-sleepable contexts. > - */ > - raw_spinlock_t aux_lock; > depot_stack_handle_t aux_stack[2]; > }; > > -- > 2.43.0.429.g432eaa2c6b-goog >