From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out28-100.mail.aliyun.com (out28-100.mail.aliyun.com [115.124.28.100]) (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 8904633ADB1; Thu, 30 Jul 2026 05:43:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.28.100 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785390215; cv=none; b=VFElupLh96e5o5rS/kDXxifa2uFU4rrveLvBNBVViiiHoMHEc44VVZJriwuG6fW2iuiK+0ymBzn0opE7Q/eAlcG9eqnihynEqr9DgERpMDBsoAzZsdf8Uy48Su9chfA9P8BZvlvkHg5Lk9oaCa91raNOJcn3yxuz5x1Siprf4oo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785390215; c=relaxed/simple; bh=3yh2x2SbQ0wTxMlakw/cJNBlV4v/tjGctSmFacwz3cg=; h=Message-ID:Date:MIME-Version:To:Cc:From:Subject:Content-Type; b=UF/y9WmNNyuWLGsAsIVWqw0tbT2R+FzgKMjTGg+tLV+eE1cQVMOnelu5ybrBTH2Ea+cNhiyNDYZLFUycx7khJRQnKhHVx4j+lZ7ogKBlEeyot7jNBG58a4mGMCpgaI8DzEt2GuJGAzoKlG9V6T46RTLiUyQ5tuMSDjp5xS3zpZ0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=allwinnertech.com; spf=pass smtp.mailfrom=allwinnertech.com; arc=none smtp.client-ip=115.124.28.100 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=allwinnertech.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=allwinnertech.com X-Alimail-AntiSpam:AC=CONTINUE;BC=0.07455114|-1;CH=green;DM=|CONTINUE|false|;DS=CONTINUE|ham_enroll_verification|0.101034-0.264635-0.634331;FP=13256837106311415166|0|0|0|0|-1|-1|-1;HT=maildocker-contentspam033037028158;MF=michael@allwinnertech.com;NM=1;PH=DS;RN=6;RT=6;SR=0;TI=SMTPD_---.iZ8Efy3_1785389880; Received: from 192.168.208.183(mailfrom:michael@allwinnertech.com fp:SMTPD_---.iZ8Efy3_1785389880 cluster:ay29) by smtp.aliyun-inc.com; Thu, 30 Jul 2026 13:38:01 +0800 Message-ID: <8147bb04-b890-f18a-9cab-48b712f54856@allwinnertech.com> Date: Thu, 30 Jul 2026 13:37:59 +0800 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Content-Language: en-US To: Steven Rostedt , Masami Hiramatsu Cc: linux-trace-kernel@vger.kernel.org, Mathieu Desnoyers , Namhyung Kim , linux-kernel@vger.kernel.org From: Michael Wu Subject: [PATCH] tracing: Fix race between update_event_fields and event_define_fields Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Kernel: Linux version 6.18.21 Platform: Android event_define_fields() (pri=1 MODULE_STATE_COMING notifier, locked by event_mutex) populates class->fields via list_add(), while update_event_fields() (called from the pri=0 notifier path via trace_event_update_all) traverses class->fields protected only by trace_event_sem. These are two different locks guarding the same data structure, so during cross-module loading a reader on one CPU can observe partially initialized list nodes being concurrently added by a writer on another CPU. On arm64 with weak memory ordering, __list_add() writes to two different cache lines: next->prev = new; // (1) ordinary store new->next = next; // (2) ordinary store — field's cache line new->prev = prev; // (3) ordinary store WRITE_ONCE(prev->next, new); // (4) release store — head's cache line The store buffer can drain (2) and (4) independently since they target different cache lines. A remote CPU may observe (4) before (2): it sees prev->next pointing to the new node, but the new node's link.next is still zero (kmem_cache_alloc zero-initialized via KMEM_CACHE with SLAB_PANIC). Since offsetof(struct ftrace_event_field, link) == 0, list_for_each_entry() derives field == NULL from link.next == 0 and crashes at field->type (offset 0x18): Unable to handle kernel access ... at virtual address 0000000000000018 pc : update_event_fields+0xf8/0x368 Call trace: update_event_fields+0xf8/0x368 trace_event_update_all+0x7c/0x2b4 trace_module_notify+0x4c/0x1dc notifier_call_chain+0x84/0x168 blocking_notifier_call_chain_robust+0x64/0xd4 load_module+0x10c8/0x123c __arm64_sys_finit_module+0x230/0x31c Fix by holding event_mutex in trace_event_update_all() before down_write(&trace_event_sem). This serializes the reader against event_define_fields() which takes event_mutex for the entire write-side critical section. The lock ordering event_mutex -> trace_event_sem is already established at three other sites (trace_remove_event_call, event_trace_add_tracer, event_trace_del_tracer), so this introduces no ordering conflict. An alternative of placing mutex_lock inside update_event_fields() was considered but rejected — it would invert the established lock ordering (trace_event_sem -> event_mutex) and risk ABBA deadlock. Signed-off-by: Michael Wu --- kernel/trace/trace_events.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 956692856fa8..9632788da5af 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -3566,6 +3566,7 @@ void trace_event_update_all(struct trace_eval_map **map, int len) int last_i; int i; + mutex_lock(&event_mutex); down_write(&trace_event_sem); list_for_each_entry_safe(call, p, &ftrace_events, list) { /* events are usually grouped together with systems */ @@ -3604,6 +3605,7 @@ void trace_event_update_all(struct trace_eval_map **map, int len) cond_resched(); } up_write(&trace_event_sem); + mutex_unlock(&event_mutex); } static bool event_in_systems(struct trace_event_call *call, -- 2.29.0 -- Regards, Michael Wu