From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp153-170.sina.com.cn (smtp153-170.sina.com.cn [61.135.153.170]) (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 22835357703 for ; Mon, 12 Jan 2026 12:09:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=61.135.153.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768219773; cv=none; b=ZIwi9Ok0umGG4sioYgTBG6f8PF/n6JYKY3ZMdIBCY0CXfc7nJCjXRg9Z0afP3nEt/fyXCcPw/QiimK85idgjCJTUN6Zz9+dVB1z1SJN9IB15M4LWdEg1nDDrjRS22fe/e2ZF6tSk2S9g8ZLOBaKsW61YjfWLa9JSXyt3vi+ScWU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768219773; c=relaxed/simple; bh=Xw/JWgYUNuV1cZtRoFoRj25PnjfpugJxt0+7G4WHJUw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RLh91NxdqfAy3WBzSB6R4XSqYAAp1mZ5F2l9VmwGQJ/THlZxwEN2k4XpL+W7DZxg9cxK9grUvcIVy9VVk7tvbf0VtBTUV0N5dmsy3zhDDM8fiVEhLPaBiH42wwHVJfwombmiIgk9qqvdUmhMljGX9X7Q6x1ZRZJ4uvupIknBYJY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com; spf=pass smtp.mailfrom=sina.com; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b=gZHmpbN2; arc=none smtp.client-ip=61.135.153.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=sina.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sina.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=sina.com header.i=@sina.com header.b="gZHmpbN2" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sina.com; s=201208; t=1768219767; bh=lG1JE0U8CdbsXhCDVRa7lpjBkh8iHi0X7zDNv0cjvGQ=; h=From:Subject:Date:Message-ID; b=gZHmpbN2SzDK4QZuA2z13/2NGMBkfNcgXeQDJ8oXu0aNsV3MJ7GWJzstZz0ps2Ae+ OxfzHn8xJuqF/skY2XJZRJCi5VjRlZ1f1ROf3JHwujFL9z/ZJGC/LIhxKhFBvIIAQ+ Gd65uNgDKV/S9NdzBrVJwU2eFp8NByBA6ApPEeoY= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([114.249.58.160]) by sina.com (10.54.253.34) with ESMTP id 6964E46900005249; Mon, 12 Jan 2026 20:09:14 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 7763946291959 X-SMAIL-UIID: 0345F1A97CE046EA83CE27B384789124-20260112-200914-1 From: Hillf Danton To: Deepanshu Kartikey Cc: Uladzislau Rezki , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Subject: Re: [PATCH v2] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node Date: Mon, 12 Jan 2026 20:08:42 +0800 Message-ID: <20260112120904.2172-1-hdanton@sina.com> In-Reply-To: <20260112103612.627247-1-kartikey406@gmail.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit #syz test When CONFIG_PAGE_OWNER is enabled, freeing KASAN shadow pages during vmalloc cleanup triggers expensive stack unwinding that acquires RCU read locks. Processing a large purge_list without rescheduling can cause the task to hold CPU for extended periods (10+ seconds), leading to RCU stalls and potential OOM conditions. The issue manifests in purge_vmap_node() -> kasan_release_vmalloc_node() where iterating through hundreds or thousands of vmap_area entries and freeing their associated shadow pages causes: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P6229/1:b..l ... task:kworker/0:17 state:R running task stack:28840 pid:6229 ... kasan_release_vmalloc_node+0x1ba/0xad0 mm/vmalloc.c:2299 purge_vmap_node+0x1ba/0xad0 mm/vmalloc.c:2299 Each call to kasan_release_vmalloc() can free many pages, and with page_owner tracking, each free triggers save_stack() which performs stack unwinding under RCU read lock. Without yielding, this creates an unbounded RCU critical section. Add periodic cond_resched() calls within the loop to allow: - RCU grace periods to complete - Other tasks to run - Scheduler to preempt when needed The fix uses need_resched() for immediate response under load, with a batch count of 32 as a guaranteed upper bound to prevent worst-case stalls even under light load. Reported-by: syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d8d4c31d40f868eaea30 Link: https://lore.kernel.org/all/20260112084723.622910-1-kartikey406@gmail.com/T/ [v1] Suggested-by: Uladzislau Rezki Signed-off-by: Deepanshu Kartikey --- v2: Use a macro for batch size (suggested by Uladzislau Rezki) --- mm/vmalloc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 41dd01e8430c..51e58701565d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2268,11 +2268,14 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) reclaim_list_global(&decay_list); } +#define KASAN_RELEASE_BATCH_SIZE 32 + static void kasan_release_vmalloc_node(struct vmap_node *vn) { struct vmap_area *va; unsigned long start, end; + unsigned int batch_count = 0; start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start; end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end; @@ -2282,6 +2285,11 @@ kasan_release_vmalloc_node(struct vmap_node *vn) kasan_release_vmalloc(va->va_start, va->va_end, va->va_start, va->va_end, KASAN_VMALLOC_PAGE_RANGE); + + if (need_resched() || (++batch_count >= KASAN_RELEASE_BATCH_SIZE)) { + cond_resched(); + batch_count = 0; + } } kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH); -- 2.43.0