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SubjectRe: [PATCH 2/5] mm/slub: use stackdepot to save stack trace in objects
On Fri, Feb 25, 2022 at 07:03:15PM +0100, Vlastimil Babka wrote:
> From: Oliver Glitta <glittao@gmail.com>
>
> Many stack traces are similar so there are many similar arrays.
> Stackdepot saves each unique stack only once.
>
> Replace field addrs in struct track with depot_stack_handle_t handle. Use
> stackdepot to save stack trace.
>
> The benefits are smaller memory overhead and possibility to aggregate
> per-cache statistics in the following patch using the stackdepot handle
> instead of matching stacks manually.
>
> [ vbabka@suse.cz: rebase to 5.17-rc1 and adjust accordingly ]
>
> This was initially merged as commit 788691464c29 and reverted by commit
> ae14c63a9f20 due to several issues, that should now be fixed.
> The problem of unconditional memory overhead by stackdepot has been
> addressed by commit 2dba5eb1c73b ("lib/stackdepot: allow optional init
> and stack_table allocation by kvmalloc()"), so the dependency on
> stackdepot will result in extra memory usage only when a slab cache
> tracking is actually enabled, and not for all CONFIG_SLUB_DEBUG builds.
> The build failures on some architectures were also addressed, and the
> reported issue with xfs/433 test did not reproduce on 5.17-rc1 with this
> patch.
>
> Signed-off-by: Oliver Glitta <glittao@gmail.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
> init/Kconfig | 1 +
> mm/slub.c | 88 +++++++++++++++++++++++++++++-----------------------
> 2 files changed, 50 insertions(+), 39 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index e9119bf54b1f..b21dd3a4a106 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1871,6 +1871,7 @@ config SLUB_DEBUG
> default y
> bool "Enable SLUB debugging support" if EXPERT
> depends on SLUB && SYSFS
> + select STACKDEPOT if STACKTRACE_SUPPORT
> help
> SLUB has extensive debug support features. Disabling these can
> result in significant savings in code size. This also disables
> diff --git a/mm/slub.c b/mm/slub.c
> index 1fc451f4fe62..3140f763e819 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -26,6 +26,7 @@
> #include <linux/cpuset.h>
> #include <linux/mempolicy.h>
> #include <linux/ctype.h>
> +#include <linux/stackdepot.h>
> #include <linux/debugobjects.h>
> #include <linux/kallsyms.h>
> #include <linux/kfence.h>
> @@ -264,8 +265,8 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
> #define TRACK_ADDRS_COUNT 16
> struct track {
> unsigned long addr; /* Called from address */
> -#ifdef CONFIG_STACKTRACE
> - unsigned long addrs[TRACK_ADDRS_COUNT]; /* Called from address */
> +#ifdef CONFIG_STACKDEPOT
> + depot_stack_handle_t handle;
> #endif
> int cpu; /* Was running on cpu */
> int pid; /* Pid context */
> @@ -724,22 +725,20 @@ static struct track *get_track(struct kmem_cache *s, void *object,
> return kasan_reset_tag(p + alloc);
> }
>
> -static void set_track(struct kmem_cache *s, void *object,
> - enum track_item alloc, unsigned long addr)
> +static noinline void
> +set_track(struct kmem_cache *s, void *object, enum track_item alloc,
> + unsigned long addr, gfp_t flags)
> {
> struct track *p = get_track(s, object, alloc);
>
> -#ifdef CONFIG_STACKTRACE
> +#ifdef CONFIG_STACKDEPOT
> + unsigned long entries[TRACK_ADDRS_COUNT];
> unsigned int nr_entries;
>
> - metadata_access_enable();
> - nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
> - TRACK_ADDRS_COUNT, 3);
> - metadata_access_disable();
> -
> - if (nr_entries < TRACK_ADDRS_COUNT)
> - p->addrs[nr_entries] = 0;
> + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
> + p->handle = stack_depot_save(entries, nr_entries, flags);
> #endif
> +
> p->addr = addr;
> p->cpu = smp_processor_id();
> p->pid = current->pid;
> @@ -759,20 +758,19 @@ static void init_tracking(struct kmem_cache *s, void *object)
>
> static void print_track(const char *s, struct track *t, unsigned long pr_time)
> {
> + depot_stack_handle_t handle __maybe_unused;
> +
> if (!t->addr)
> return;
>
> pr_err("%s in %pS age=%lu cpu=%u pid=%d\n",
> s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
> -#ifdef CONFIG_STACKTRACE
> - {
> - int i;
> - for (i = 0; i < TRACK_ADDRS_COUNT; i++)
> - if (t->addrs[i])
> - pr_err("\t%pS\n", (void *)t->addrs[i]);
> - else
> - break;
> - }
> +#ifdef CONFIG_STACKDEPOT
> + handle = READ_ONCE(t->handle);
> + if (handle)
> + stack_depot_print(handle);
> + else
> + pr_err("object allocation/free stack trace missing\n");
> #endif
> }
>
> @@ -1304,9 +1302,9 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
> return 1;
> }
>
> -static noinline int alloc_debug_processing(struct kmem_cache *s,
> - struct slab *slab,
> - void *object, unsigned long addr)
> +static noinline int
> +alloc_debug_processing(struct kmem_cache *s, struct slab *slab, void *object,
> + unsigned long addr, gfp_t flags)
> {
> if (s->flags & SLAB_CONSISTENCY_CHECKS) {
> if (!alloc_consistency_checks(s, slab, object))
> @@ -1315,7 +1313,7 @@ static noinline int alloc_debug_processing(struct kmem_cache *s,
>
> /* Success perform special debug activities for allocs */
> if (s->flags & SLAB_STORE_USER)
> - set_track(s, object, TRACK_ALLOC, addr);
> + set_track(s, object, TRACK_ALLOC, addr, flags);

I see warning because of this.
We should not reuse flags here because alloc_debug_processing() can be
called with preemption disabled, and caller specified GFP_KERNEL.

[ 2.015902] BUG: sleeping function called from invalid context at mm/page_alloc.c:5164
[ 2.022052] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0
[ 2.028357] preempt_count: 1, expected: 0
[ 2.031508] RCU nest depth: 0, expected: 0
[ 2.034722] 1 lock held by swapper/0/1:
[ 2.037905] #0: ffff00000488f4d0 (&sb->s_type->i_mutex_key#5){+.+.}-{4:4}, at: start_creating+0x58/0x130
[ 2.045393] Preemption disabled at:
[ 2.045400] [<ffff8000083bd008>] __slab_alloc.constprop.0+0x38/0xc0
[ 2.053039] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 5.17.0-rc5+ #105
[ 2.059365] Hardware name: linux,dummy-virt (DT)
[ 2.063160] Call trace:
[ 2.065217] dump_backtrace+0xf8/0x130
[ 2.068350] show_stack+0x24/0x80
[ 2.071104] dump_stack_lvl+0x9c/0xd8
[ 2.074140] dump_stack+0x18/0x34
[ 2.076894] __might_resched+0x1a0/0x280
[ 2.080146] __might_sleep+0x58/0x90
[ 2.083108] prepare_alloc_pages.constprop.0+0x1b4/0x1f0
[ 2.087468] __alloc_pages+0x88/0x1e0
[ 2.090502] alloc_page_interleave+0x24/0xb4
[ 2.094021] alloc_pages+0x10c/0x170
[ 2.096984] __stack_depot_save+0x3e0/0x4e0
[ 2.100446] stack_depot_save+0x14/0x20
[ 2.103617] set_track.isra.0+0x64/0xa4
[ 2.106787] alloc_debug_processing+0x11c/0x1e0
[ 2.110532] ___slab_alloc+0x3e8/0x750
[ 2.113643] __slab_alloc.constprop.0+0x64/0xc0
[ 2.117391] kmem_cache_alloc+0x304/0x350
[ 2.120702] security_inode_alloc+0x38/0xa4
[ 2.124169] inode_init_always+0xd0/0x264
[ 2.127501] alloc_inode+0x44/0xec
[ 2.130325] new_inode+0x28/0xc0
[ 2.133011] tracefs_create_file+0x74/0x1e0
[ 2.136459] init_tracer_tracefs+0x248/0x644
[ 2.140030] tracer_init_tracefs+0x9c/0x34c
[ 2.143483] do_one_initcall+0x44/0x170
[ 2.146654] do_initcalls+0x104/0x144
[ 2.149704] kernel_init_freeable+0x130/0x178

[...]

> trace(s, slab, object, 1);
> init_object(s, object, SLUB_RED_ACTIVE);
> return 1;
> @@ -1395,7 +1393,7 @@ static noinline int free_debug_processing(
> }
>
> if (s->flags & SLAB_STORE_USER)
> - set_track(s, object, TRACK_FREE, addr);
> + set_track(s, object, TRACK_FREE, addr, GFP_NOWAIT);
> trace(s, slab, object, 0);
> /* Freepointer not overwritten by init_object(), SLAB_POISON moved it */
> init_object(s, object, SLUB_RED_INACTIVE);
> @@ -1632,7 +1630,8 @@ static inline
> void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr) {}
>
> static inline int alloc_debug_processing(struct kmem_cache *s,
> - struct slab *slab, void *object, unsigned long addr) { return 0; }
> + struct slab *slab, void *object, unsigned long addr,
> + gfp_t flags) { return 0; }
>
> static inline int free_debug_processing(
> struct kmem_cache *s, struct slab *slab,
> @@ -3033,7 +3032,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> check_new_slab:
>
> if (kmem_cache_debug(s)) {
> - if (!alloc_debug_processing(s, slab, freelist, addr)) {
> + if (!alloc_debug_processing(s, slab, freelist, addr, gfpflags)) {
> /* Slab failed checks. Next slab needed */
> goto new_slab;
> } else {
> @@ -4221,6 +4220,9 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> s->remote_node_defrag_ratio = 1000;
> #endif
>
> + if (s->flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
> + stack_depot_init();
> +

As mentioned in my report, it can crash system when creating boot caches
with debugging enabled.

The rest looks fine!

> /* Initialize the pre-computed randomized freelist if slab is up */
> if (slab_state >= UP) {
> if (init_cache_random_seq(s))
> @@ -4352,18 +4354,26 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
> objp = fixup_red_left(s, objp);
> trackp = get_track(s, objp, TRACK_ALLOC);
> kpp->kp_ret = (void *)trackp->addr;
> -#ifdef CONFIG_STACKTRACE
> - for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> - kpp->kp_stack[i] = (void *)trackp->addrs[i];
> - if (!kpp->kp_stack[i])
> - break;
> - }
> +#ifdef CONFIG_STACKDEPOT
> + {
> + depot_stack_handle_t handle;
> + unsigned long *entries;
> + unsigned int nr_entries;
> +
> + handle = READ_ONCE(trackp->handle);
> + if (handle) {
> + nr_entries = stack_depot_fetch(handle, &entries);
> + for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> + kpp->kp_stack[i] = (void *)entries[i];
> + }
>
> - trackp = get_track(s, objp, TRACK_FREE);
> - for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> - kpp->kp_free_stack[i] = (void *)trackp->addrs[i];
> - if (!kpp->kp_free_stack[i])
> - break;
> + trackp = get_track(s, objp, TRACK_FREE);
> + handle = READ_ONCE(trackp->handle);
> + if (handle) {
> + nr_entries = stack_depot_fetch(handle, &entries);
> + for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> + kpp->kp_free_stack[i] = (void *)entries[i];
> + }
> }
> #endif
> #endif
> --
> 2.35.1
>
>

--
Thank you, You are awesome!
Hyeonggon :-)

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