From nobody Sat Feb 7 10:08:09 2026 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F311515C129 for ; Mon, 12 Aug 2024 07:00:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723446007; cv=none; b=a2cCa+Lsix7rdCKhi3grfraGED69mwetWLxh2jQUyaAdNuMFcP7CTewrMd982sza6ycR3Om5f8AcpAXz3Oo0gFU5H9o62VnWswUoqjT3hk0DJ1qM/K8LNpxLkd9Oi7FcMuSlgUly7lkWv559eN3uwpjbHrnRbWnUUU81PID4vQU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723446007; c=relaxed/simple; bh=Hl3o28OEHxharHUo5EPEcmIKtXI10Pywg9Bpi+sw9DE=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=RZWOyK3p4UQz17Is/z9Gp0MJlZpfO8o2tK/w7t4biA9IEMx4ifpUimWr7xo1u+vk5Jr6NertTzTD3sRpXHxM2yK323nxBl+T3wKwjxoLWwWH8EO1Mop0D4ng34ifmytPhcj0ALHyXw0zLz8M3P1EvqCaBitpqDhz4p3wragJfzw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=wRJPCz82; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="wRJPCz82" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1723445996; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=2sB5TDcVkqlobWIVqrnBXmc0iuAglrquanWdPCiDDFo=; b=wRJPCz82B0LAOgJIjLAlwtGWlNx6UJhyKGXE78VBMy1q6xnt728Sd7mzk0LNqHHT/bR6k3z2cIIXtez301jFStsUW7EML+HnMLmyHZEm4esYzPSuHHbnswB4bKVsILJdC66HqFz/4NenkwKnvA64pUYK5l0f8tRAUVPRsG/pRgM= Received: from localhost.localdomain(mailfrom:dtcccc@linux.alibaba.com fp:SMTPD_---0WCaX4Nj_1723445987) by smtp.aliyun-inc.com; Mon, 12 Aug 2024 14:59:55 +0800 From: Tianchen Ding To: linux-kernel@vger.kernel.org Cc: Marco Elver , Alexander Potapenko , Dmitry Vyukov , Andrew Morton , kasan-dev@googlegroups.com, linux-mm@kvack.org Subject: [PATCH] kfence: Save freeing stack trace at calling time instead of freeing time Date: Mon, 12 Aug 2024 14:59:47 +0800 Message-Id: <20240812065947.6104-1-dtcccc@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For kmem_cache with SLAB_TYPESAFE_BY_RCU, the freeing trace stack at calling kmem_cache_free() is more useful. While the following stack is meaningless and provides no help: freed by task 46 on cpu 0 at 656.840729s: rcu_do_batch+0x1ab/0x540 nocb_cb_wait+0x8f/0x260 rcu_nocb_cb_kthread+0x25/0x80 kthread+0xd2/0x100 ret_from_fork+0x34/0x50 ret_from_fork_asm+0x1a/0x30 Signed-off-by: Tianchen Ding --- I'm not sure whether we should keep KFENCE_OBJECT_FREED info remained (maybe the exact free time can be helpful?). But add a new kfence_track will cost more memory, so I prefer to reuse free_track and drop the info when when KFENCE_OBJECT_RCU_FREEING -> KFENCE_OBJECT_FREED. --- mm/kfence/core.c | 35 ++++++++++++++++++++++++++--------- mm/kfence/kfence.h | 1 + mm/kfence/report.c | 7 ++++--- 3 files changed, 31 insertions(+), 12 deletions(-) diff --git a/mm/kfence/core.c b/mm/kfence/core.c index c5cb54fc696d..89469d4f2d95 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -269,6 +269,13 @@ static inline unsigned long metadata_to_pageaddr(const= struct kfence_metadata *m return pageaddr; } =20 +static bool kfence_obj_inuse(const struct kfence_metadata *meta) +{ + enum kfence_object_state state =3D READ_ONCE(meta->state); + + return state =3D=3D KFENCE_OBJECT_ALLOCATED || state =3D=3D KFENCE_OBJECT= _RCU_FREEING; +} + /* * Update the object's metadata state, including updating the alloc/free s= tacks * depending on the state transition. @@ -278,10 +285,14 @@ metadata_update_state(struct kfence_metadata *meta, e= num kfence_object_state nex unsigned long *stack_entries, size_t num_stack_entries) { struct kfence_track *track =3D - next =3D=3D KFENCE_OBJECT_FREED ? &meta->free_track : &meta->alloc_track; + next =3D=3D KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_t= rack; =20 lockdep_assert_held(&meta->lock); =20 + /* Stack has been saved when calling rcu, skip. */ + if (READ_ONCE(meta->state) =3D=3D KFENCE_OBJECT_RCU_FREEING) + goto out; + if (stack_entries) { memcpy(track->stack_entries, stack_entries, num_stack_entries * sizeof(stack_entries[0])); @@ -297,6 +308,7 @@ metadata_update_state(struct kfence_metadata *meta, enu= m kfence_object_state nex track->cpu =3D raw_smp_processor_id(); track->ts_nsec =3D local_clock(); /* Same source as printk timestamps. */ =20 +out: /* * Pairs with READ_ONCE() in * kfence_shutdown_cache(), @@ -502,7 +514,7 @@ static void kfence_guarded_free(void *addr, struct kfen= ce_metadata *meta, bool z =20 raw_spin_lock_irqsave(&meta->lock, flags); =20 - if (meta->state !=3D KFENCE_OBJECT_ALLOCATED || meta->addr !=3D (unsigned= long)addr) { + if (!kfence_obj_inuse(meta) || meta->addr !=3D (unsigned long)addr) { /* Invalid or double-free, bail out. */ atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); kfence_report_error((unsigned long)addr, false, NULL, meta, @@ -780,7 +792,7 @@ static void kfence_check_all_canary(void) for (i =3D 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { struct kfence_metadata *meta =3D &kfence_metadata[i]; =20 - if (meta->state =3D=3D KFENCE_OBJECT_ALLOCATED) + if (kfence_obj_inuse(meta)) check_canary(meta); } } @@ -1006,12 +1018,11 @@ void kfence_shutdown_cache(struct kmem_cache *s) * the lock will not help, as different critical section * serialization will have the same outcome. */ - if (READ_ONCE(meta->cache) !=3D s || - READ_ONCE(meta->state) !=3D KFENCE_OBJECT_ALLOCATED) + if (READ_ONCE(meta->cache) !=3D s || !kfence_obj_inuse(meta)) continue; =20 raw_spin_lock_irqsave(&meta->lock, flags); - in_use =3D meta->cache =3D=3D s && meta->state =3D=3D KFENCE_OBJECT_ALLO= CATED; + in_use =3D meta->cache =3D=3D s && kfence_obj_inuse(meta); raw_spin_unlock_irqrestore(&meta->lock, flags); =20 if (in_use) { @@ -1145,6 +1156,7 @@ void *kfence_object_start(const void *addr) void __kfence_free(void *addr) { struct kfence_metadata *meta =3D addr_to_metadata((unsigned long)addr); + unsigned long flags; =20 #ifdef CONFIG_MEMCG KFENCE_WARN_ON(meta->obj_exts.objcg); @@ -1154,9 +1166,14 @@ void __kfence_free(void *addr) * the object, as the object page may be recycled for other-typed * objects once it has been freed. meta->cache may be NULL if the cache * was destroyed. + * Save the stack trace here. It is more useful. */ - if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) + if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU)))= { + raw_spin_lock_irqsave(&meta->lock, flags); + metadata_update_state(meta, KFENCE_OBJECT_RCU_FREEING, NULL, 0); + raw_spin_unlock_irqrestore(&meta->lock, flags); call_rcu(&meta->rcu_head, rcu_guarded_free); + } else kfence_guarded_free(addr, meta, false); } @@ -1182,14 +1199,14 @@ bool kfence_handle_page_fault(unsigned long addr, b= ool is_write, struct pt_regs int distance =3D 0; =20 meta =3D addr_to_metadata(addr - PAGE_SIZE); - if (meta && READ_ONCE(meta->state) =3D=3D KFENCE_OBJECT_ALLOCATED) { + if (meta && kfence_obj_inuse(meta)) { to_report =3D meta; /* Data race ok; distance calculation approximate. */ distance =3D addr - data_race(meta->addr + meta->size); } =20 meta =3D addr_to_metadata(addr + PAGE_SIZE); - if (meta && READ_ONCE(meta->state) =3D=3D KFENCE_OBJECT_ALLOCATED) { + if (meta && kfence_obj_inuse(meta)) { /* Data race ok; distance calculation approximate. */ if (!to_report || distance > data_race(meta->addr) - addr) to_report =3D meta; diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h index db87a05047bd..dfba5ea06b01 100644 --- a/mm/kfence/kfence.h +++ b/mm/kfence/kfence.h @@ -38,6 +38,7 @@ enum kfence_object_state { KFENCE_OBJECT_UNUSED, /* Object is unused. */ KFENCE_OBJECT_ALLOCATED, /* Object is currently allocated. */ + KFENCE_OBJECT_RCU_FREEING, /* Object was allocated, and then being freed = by rcu. */ KFENCE_OBJECT_FREED, /* Object was allocated, and then freed. */ }; =20 diff --git a/mm/kfence/report.c b/mm/kfence/report.c index 73a6fe42845a..451991a3a8f2 100644 --- a/mm/kfence/report.c +++ b/mm/kfence/report.c @@ -114,7 +114,8 @@ static void kfence_print_stack(struct seq_file *seq, co= nst struct kfence_metadat =20 /* Timestamp matches printk timestamp format. */ seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus (%lu.%06lus ag= o):\n", - show_alloc ? "allocated" : "freed", track->pid, + show_alloc ? "allocated" : meta->state =3D=3D KFENCE_OBJECT_RCU_F= REEING ? + "rcu freeing" : "freed", track->pid, track->cpu, (unsigned long)ts_sec, rem_nsec / 1000, (unsigned long)interval_nsec, rem_interval_nsec / 1000); =20 @@ -149,7 +150,7 @@ void kfence_print_object(struct seq_file *seq, const st= ruct kfence_metadata *met =20 kfence_print_stack(seq, meta, true); =20 - if (meta->state =3D=3D KFENCE_OBJECT_FREED) { + if (meta->state =3D=3D KFENCE_OBJECT_FREED || meta->state =3D=3D KFENCE_O= BJECT_RCU_FREEING) { seq_con_printf(seq, "\n"); kfence_print_stack(seq, meta, false); } @@ -318,7 +319,7 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void = *object, struct slab *sla kpp->kp_slab_cache =3D meta->cache; kpp->kp_objp =3D (void *)meta->addr; kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack); - if (meta->state =3D=3D KFENCE_OBJECT_FREED) + if (meta->state =3D=3D KFENCE_OBJECT_FREED || meta->state =3D=3D KFENCE_O= BJECT_RCU_FREEING) kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack); /* get_stack_skipnr() ensures the first entry is outside allocator. */ kpp->kp_ret =3D kpp->kp_stack[0]; --=20 2.39.3