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SubjectRe: [PATCH 2/5] mm/slub: use stackdepot to save stack trace in objects
On 2/26/22 11:24, Hyeonggon Yoo wrote:
> 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.

Ugh, thanks for catching this, looks like I forgot to test with necessary
config options. Indeed the previous version of this patch that was commit
788691464c29 used GFP_NOWAIT. I have used the idea to pass allocation
gfpflags from Imran's version (another Cc I forgot, sorry)
https://lore.kernel.org/all/20210831062539.898293-3-imran.f.khan@oracle.com/
...

> [ 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

... but indeed __slab_alloc() disables preemption so that won't work, and we
can only safely use GFP_NOWAIT. Will fix in v2, thanks.

> [ 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
>>
>>
>

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