Re: [PATCH 14/16] mm/slab_common: drop kmem_alloc & avoid dereferencing fields when not using

From: Vlastimil Babka
Date: Fri Jul 29 2022 - 07:23:45 EST

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On 7/12/22 15:39, Hyeonggon Yoo wrote:
> Drop kmem_alloc event class, and define kmalloc and kmem_cache_alloc
> using TRACE_EVENT() macro.
>
> And then this patch does:
> - Do not pass pointer to struct kmem_cache to trace_kmalloc.
> gfp flag is enough to know if it's accounted or not.
> - Avoid dereferencing s->object_size and s->size when not using kmem_cache_alloc event.
> - Avoid dereferencing s->name in when not using kmem_cache_free event.
>
> Suggested-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>

With some comments:

> ---
> include/trace/events/kmem.h | 64 +++++++++++++++++++++++++------------
> mm/slab.c | 16 ++++------
> mm/slab_common.c | 17 ++++++----
> mm/slob.c | 16 +++-------
> mm/slub.c | 13 +++-----
> 5 files changed, 70 insertions(+), 56 deletions(-)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index e078ebcdc4b1..0ded2c351062 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -9,17 +9,15 @@
> #include <linux/tracepoint.h>
> #include <trace/events/mmflags.h>
>
> -DECLARE_EVENT_CLASS(kmem_alloc,
> +TRACE_EVENT(kmem_cache_alloc,
>
> TP_PROTO(unsigned long call_site,
> const void *ptr,
> struct kmem_cache *s,
> - size_t bytes_req,
> - size_t bytes_alloc,
> gfp_t gfp_flags,
> int node),
>
> - TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node),
> + TP_ARGS(call_site, ptr, s, gfp_flags, node),
>
> TP_STRUCT__entry(
> __field( unsigned long, call_site )
> @@ -34,8 +32,8 @@ DECLARE_EVENT_CLASS(kmem_alloc,
> TP_fast_assign(
> __entry->call_site = call_site;
> __entry->ptr = ptr;
> - __entry->bytes_req = bytes_req;
> - __entry->bytes_alloc = bytes_alloc;
> + __entry->bytes_req = s->object_size;
> + __entry->bytes_alloc = s->size;
> __entry->gfp_flags = (__force unsigned long)gfp_flags;
> __entry->node = node;
> __entry->accounted = IS_ENABLED(CONFIG_MEMCG_KMEM) ?

This assignment continues by ...
(s && s->flags & SLAB_ACCOUNT)) : false;

We could now remove the "s &&" as we assume it's non-NULL anyway.

> @@ -53,22 +51,46 @@ DECLARE_EVENT_CLASS(kmem_alloc,
> __entry->accounted ? "true" : "false")
> );
>
> -DEFINE_EVENT(kmem_alloc, kmalloc,
> +TRACE_EVENT(kmalloc,
>
> - TP_PROTO(unsigned long call_site, const void *ptr,
> - struct kmem_cache *s, size_t bytes_req, size_t bytes_alloc,
> - gfp_t gfp_flags, int node),
> + TP_PROTO(unsigned long call_site,
> + const void *ptr,
> + size_t bytes_req,
> + size_t bytes_alloc,
> + gfp_t gfp_flags,
> + int node),
>
> - TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node)
> -);
> + TP_ARGS(call_site, ptr, bytes_req, bytes_alloc, gfp_flags, node),
>
> -DEFINE_EVENT(kmem_alloc, kmem_cache_alloc,
> + TP_STRUCT__entry(
> + __field( unsigned long, call_site )
> + __field( const void *, ptr )
> + __field( size_t, bytes_req )
> + __field( size_t, bytes_alloc )
> + __field( unsigned long, gfp_flags )
> + __field( int, node )
> + __field( bool, accounted )
> + ),
>
> - TP_PROTO(unsigned long call_site, const void *ptr,
> - struct kmem_cache *s, size_t bytes_req, size_t bytes_alloc,
> - gfp_t gfp_flags, int node),
> + TP_fast_assign(
> + __entry->call_site = call_site;
> + __entry->ptr = ptr;
> + __entry->bytes_req = bytes_req;
> + __entry->bytes_alloc = bytes_alloc;
> + __entry->gfp_flags = (__force unsigned long)gfp_flags;
> + __entry->node = node;
> + __entry->accounted = IS_ENABLED(CONFIG_MEMCG_KMEM) ?
> + (gfp_flags & __GFP_ACCOUNT) : false;

This test could be perhaps moved to TP_printk and the accounted field
removed completely, but we need to make sure trace-cmd (which reads the
binary entries and does the printk in userspace) can interpret the tests
properly, including the IS_ENABLED(CONFIG_MEMCG_KMEM) part.

> + ),
>
> - TP_ARGS(call_site, ptr, s, bytes_req, bytes_alloc, gfp_flags, node)
> + TP_printk("call_site=%pS ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d accounted=%s",
> + (void *)__entry->call_site,
> + __entry->ptr,
> + __entry->bytes_req,
> + __entry->bytes_alloc,
> + show_gfp_flags(__entry->gfp_flags),
> + __entry->node,
> + __entry->accounted ? "true" : "false")
> );
>
> TRACE_EVENT(kfree,
> @@ -93,20 +115,20 @@ TRACE_EVENT(kfree,
>
> TRACE_EVENT(kmem_cache_free,
>
> - TP_PROTO(unsigned long call_site, const void *ptr, const char *name),
> + TP_PROTO(unsigned long call_site, const void *ptr, const struct kmem_cache *s),
>
> - TP_ARGS(call_site, ptr, name),
> + TP_ARGS(call_site, ptr, s),
>
> TP_STRUCT__entry(
> __field( unsigned long, call_site )
> __field( const void *, ptr )
> - __string( name, name )
> + __string( name, s->name )
> ),
>
> TP_fast_assign(
> __entry->call_site = call_site;
> __entry->ptr = ptr;
> - __assign_str(name, name);
> + __assign_str(name, s->name);
> ),
>
> TP_printk("call_site=%pS ptr=%p name=%s",
> diff --git a/mm/slab.c b/mm/slab.c
> index f9b74831e3f4..1685e5507a59 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3447,8 +3447,7 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *cachep, struct list_lru *lru,
> {
> void *ret = slab_alloc(cachep, lru, flags, cachep->object_size, _RET_IP_);
>
> - trace_kmem_cache_alloc(_RET_IP_, ret, cachep, cachep->object_size,
> - cachep->size, flags, NUMA_NO_NODE);
> + trace_kmem_cache_alloc(_RET_IP_, ret, cachep, flags, NUMA_NO_NODE);
>
> return ret;
> }
> @@ -3537,8 +3536,9 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
> ret = slab_alloc(cachep, NULL, flags, size, _RET_IP_);
>
> ret = kasan_kmalloc(cachep, ret, size, flags);
> - trace_kmalloc(_RET_IP_, ret, cachep,
> - size, cachep->size, flags, NUMA_NO_NODE);
> + trace_kmalloc(_RET_IP_, ret,
> + size, cachep->size,
> + flags, NUMA_NO_NODE);

This could now fit on 2, maybe even 1 line?
Other trace_* calls could be perhaps also reduced, please check.

> return ret;
> }
> EXPORT_SYMBOL(kmem_cache_alloc_trace);
> @@ -3561,9 +3561,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid)
> {
> void *ret = slab_alloc_node(cachep, NULL, flags, nodeid, cachep->object_size, _RET_IP_);
>
> - trace_kmem_cache_alloc(_RET_IP_, ret, cachep,
> - cachep->object_size, cachep->size,
> - flags, nodeid);
> + trace_kmem_cache_alloc(_RET_IP_, ret, cachep, flags, nodeid);
>
> return ret;
> }
> @@ -3588,7 +3586,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
> ret = slab_alloc_node(cachep, NULL, flags, nodeid, size, _RET_IP_);
>
> ret = kasan_kmalloc(cachep, ret, size, flags);
> - trace_kmalloc(_RET_IP_, ret, cachep,
> + trace_kmalloc(_RET_IP_, ret,
> size, cachep->size,
> flags, nodeid);
> return ret;
> @@ -3652,7 +3650,7 @@ void kmem_cache_free(struct kmem_cache *cachep, void *objp)
> if (!cachep)
> return;
>
> - trace_kmem_cache_free(_RET_IP_, objp, cachep->name);
> + trace_kmem_cache_free(_RET_IP_, objp, cachep);
> __do_kmem_cache_free(cachep, objp, _RET_IP_);
> }
> EXPORT_SYMBOL(kmem_cache_free);
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 0e66b4911ebf..c01c6b8f0d34 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -933,7 +933,7 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
>
> if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> ret = kmalloc_large_node_notrace(size, flags, node);
> - trace_kmalloc(_RET_IP_, ret, NULL,
> + trace_kmalloc(_RET_IP_, ret,
> size, PAGE_SIZE << get_order(size),
> flags, node);
> return ret;
> @@ -946,8 +946,9 @@ void *__do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller
>
> ret = __kmem_cache_alloc_node(s, flags, node, size, caller);
> ret = kasan_kmalloc(s, ret, size, flags);
> - trace_kmalloc(_RET_IP_, ret, s, size,
> - s->size, flags, node);
> + trace_kmalloc(_RET_IP_, ret,
> + size, s->size,
> + flags, node);
> return ret;
> }
>
> @@ -1075,8 +1076,9 @@ void *kmalloc_large(size_t size, gfp_t flags)
> {
> void *ret = __kmalloc_large_node_notrace(size, flags, NUMA_NO_NODE);
>
> - trace_kmalloc(_RET_IP_, ret, NULL, size,
> - PAGE_SIZE << get_order(size), flags, NUMA_NO_NODE);
> + trace_kmalloc(_RET_IP_, ret,
> + size, PAGE_SIZE << get_order(size),
> + flags, NUMA_NO_NODE);
> return ret;
> }
> EXPORT_SYMBOL(kmalloc_large);
> @@ -1090,8 +1092,9 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node)
> {
> void *ret = __kmalloc_large_node_notrace(size, flags, node);
>
> - trace_kmalloc(_RET_IP_, ret, NULL, size,
> - PAGE_SIZE << get_order(size), flags, node);
> + trace_kmalloc(_RET_IP_, ret,
> + size, PAGE_SIZE << get_order(size),
> + flags, node);
> return ret;
> }
> EXPORT_SYMBOL(kmalloc_large_node);
> diff --git a/mm/slob.c b/mm/slob.c
> index a4d50d957c25..97a4d2407f96 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -507,8 +507,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> *m = size;
> ret = (void *)m + minalign;
>
> - trace_kmalloc(caller, ret, NULL,
> - size, size + minalign, gfp, node);
> + trace_kmalloc(caller, ret, size, size + minalign, gfp, node);
> } else {
> unsigned int order = get_order(size);
>
> @@ -516,8 +515,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
> gfp |= __GFP_COMP;
> ret = slob_new_pages(gfp, order, node);
>
> - trace_kmalloc(caller, ret, NULL,
> - size, PAGE_SIZE << order, gfp, node);
> + trace_kmalloc(caller, ret, size, PAGE_SIZE << order, gfp, node);
> }
>
> kmemleak_alloc(ret, size, 1, gfp);
> @@ -608,14 +606,10 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
>
> if (c->size < PAGE_SIZE) {
> b = slob_alloc(c->size, flags, c->align, node, 0);
> - trace_kmem_cache_alloc(_RET_IP_, b, NULL, c->object_size,
> - SLOB_UNITS(c->size) * SLOB_UNIT,

Hm we lose the SLOB_UNITS() adjustment here. Maybe we don't care that much,
maybe simply c->size could be already stored with SLOB_UNITS() (but didn't
check if other stuff breaks with that).

Thanks!

> - flags, node);
> + trace_kmem_cache_alloc(_RET_IP_, b, c, flags, node);
> } else {
> b = slob_new_pages(flags, get_order(c->size), node);
> - trace_kmem_cache_alloc(_RET_IP_, b, NULL, c->object_size,
> - PAGE_SIZE << get_order(c->size),
> - flags, node);
> + trace_kmem_cache_alloc(_RET_IP_, b, c, flags, node);
> }
>
> if (b && c->ctor) {
> @@ -671,7 +665,7 @@ static void kmem_rcu_free(struct rcu_head *head)
> void kmem_cache_free(struct kmem_cache *c, void *b)
> {
> kmemleak_free_recursive(b, c->flags);
> - trace_kmem_cache_free(_RET_IP_, b, c->name);
> + trace_kmem_cache_free(_RET_IP_, b, c);
> if (unlikely(c->flags & SLAB_TYPESAFE_BY_RCU)) {
> struct slob_rcu *slob_rcu;
> slob_rcu = b + (c->size - sizeof(struct slob_rcu));
> diff --git a/mm/slub.c b/mm/slub.c
> index f1aa51480dc4..a49c69469c64 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3243,8 +3243,7 @@ void *__kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
> {
> void *ret = slab_alloc(s, lru, gfpflags, _RET_IP_, s->object_size);
>
> - trace_kmem_cache_alloc(_RET_IP_, ret, s, s->object_size,
> - s->size, gfpflags, NUMA_NO_NODE);
> + trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, NUMA_NO_NODE);
>
> return ret;
> }
> @@ -3274,7 +3273,7 @@ void *__kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags,
> void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
> {
> void *ret = slab_alloc(s, NULL, gfpflags, _RET_IP_, size);
> - trace_kmalloc(_RET_IP_, ret, s, size, s->size, gfpflags, NUMA_NO_NODE);
> + trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags, NUMA_NO_NODE);
> ret = kasan_kmalloc(s, ret, size, gfpflags);
> return ret;
> }
> @@ -3285,8 +3284,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, int node)
> {
> void *ret = slab_alloc_node(s, NULL, gfpflags, node, _RET_IP_, s->object_size);
>
> - trace_kmem_cache_alloc(_RET_IP_, ret, s,
> - s->object_size, s->size, gfpflags, node);
> + trace_kmem_cache_alloc(_RET_IP_, ret, s, gfpflags, node);
>
> return ret;
> }
> @@ -3299,8 +3297,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
> {
> void *ret = slab_alloc_node(s, NULL, gfpflags, node, _RET_IP_, size);
>
> - trace_kmalloc(_RET_IP_, ret, s,
> - size, s->size, gfpflags, node);
> + trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags, node);
>
> ret = kasan_kmalloc(s, ret, size, gfpflags);
> return ret;
> @@ -3544,7 +3541,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
> s = cache_from_obj(s, x);
> if (!s)
> return;
> - trace_kmem_cache_free(_RET_IP_, x, s->name);
> + trace_kmem_cache_free(_RET_IP_, x, s);
> slab_free(s, virt_to_slab(x), x, NULL, &x, 1, _RET_IP_);
> }
> EXPORT_SYMBOL(kmem_cache_free);

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