From nobody Mon May 25 01:15:23 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 633C63ED5CC for ; Tue, 19 May 2026 22:25:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779229549; cv=none; b=OQGuos4sIMaupEh7JwGIy9yXjep1yKGtmX9Ft5bUKEAnJojxlOgLA7AvuPr3g2ZCxNSFT4IBvge5xT+fDiTl13J6pkCoUapqa64waku01/d5fTrgPigcfqtAh/9j9RsPk1SztyIqpQ8wGdQCq8WcUxUa3eYFnZ2MzeKeRCM6bws= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779229549; c=relaxed/simple; bh=oibJLxIdOuJ1vEqW4cJ9mljoRJ9W4FXNz8lH/bKq6hY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=kKgC56gkf9wwYI/KGY+H9ugqFoPGBCk4jojztPDDuH62ODN69+MxOnCb6Fs3q/BeBb8x5rrGin6qgCRKZJgwjU1NvYBlS69/t0h/fCH8vJJr7Ppu9/ThX8/XhnYzJm8mp0Y6/3N4pQ5mnMpggjPiDJgXw17AMPCoIYxX5ekxooc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Kj7xg5qq; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Kj7xg5qq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1779229547; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=vAB44BGqZ+fuUDNGrRoAE7PFPdrgJUI60GqrOp9DD1k=; b=Kj7xg5qqZBl9Ni6a9meystcB1MMmJKy2Pbq7f8zYHZ4e6BOE/LloP/jMBfryoKVzcpAyxi BLsaoonE8ZYfRuAbJk+In5H6OKZLXMAS5Tixv53X2waHwSD/LAqD6M/oFUssE+XkkEI7NE dMXEJLU22XMbLqt2pD0mKxtXx81dXxw= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-459-AzZW7v-RMy2avixHHnyFbw-1; Tue, 19 May 2026 18:25:42 -0400 X-MC-Unique: AzZW7v-RMy2avixHHnyFbw-1 X-Mimecast-MFC-AGG-ID: AzZW7v-RMy2avixHHnyFbw_1779229540 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DCCCD1956046; Tue, 19 May 2026 22:25:39 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.65.90]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 04B5519560A2; Tue, 19 May 2026 22:25:36 +0000 (UTC) From: Waiman Long To: Catalin Marinas , Will Deacon , Mark Rutland , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Waiman Long Subject: [PATCH] arm64/entry: Don't disable preemption in debug_exception_enter() with RT kernel Date: Tue, 19 May 2026 18:25:24 -0400 Message-ID: <20260519222524.886454-1-longman@redhat.com> 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 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Content-Type: text/plain; charset="utf-8" Commit d8bb6718c4db ("arm64: Make debug exception handlers visible from RCU") introduces debug_exception_enter() and debug_exception_exit() where preemption is explicitly disabled. With a PREEMPT_RT debug kernel, the following bug report can happen. BUG: sleeping function called from invalid context at kernel/locking/spin= lock_rt.c:48 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15255, name: gdb_a= pp preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 1 lock held by gdb_app/15255: #0: ffff10007f41b7d8 (&sighand->siglock){..}-{3:3}, at: force_sig_info_to= _task+0x34/0x130 Preemption disabled at: [] debug_exception_enter+0x18/0x70 : Call trace: dump_backtrace+0xac/0x130 show_stack+0x1c/0x24 dump_stack_lvl+0xa0/0xe0 dump_stack+0x14/0x2c __might_resched+0x178/0x230 rt_spin_lock+0x58/0x120 force_sig_info_to_task+0x34/0x130 force_sig_fault+0x58/0x80 arm64_force_sig_fault+0x44/0x70 send_user_sigtrap+0x5c/0xa0 brk_handler+0x38/0x5c do_debug_exception+0x78/0x110 el0_dbg+0x50/0x1e0 el0t_64_sync_handler+0x114/0x150 el0t_64_sync+0x17c/0x180 Fix that by blocking the preempt_disable()/preempt_enable_no_resched() calls when CONFIG_PREEMPT_RT is enabled. Signed-off-by: Waiman Long --- arch/arm64/kernel/entry-common.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-com= mon.c index c7a23f7c2212..191441b22b7c 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -290,15 +290,17 @@ static __always_inline void fpsimd_syscall_exit(void) } =20 /* - * In debug exception context, we explicitly disable preemption despite - * having interrupts disabled. + * In debug exception context, we explicitly disable preemption except for + * PREEMPT_RT kernel as rt_spin_lock() can be called. + * * This serves two purposes: it makes it much less likely that we would * accidentally schedule in exception context and it will force a warning * if we somehow manage to schedule by accident. */ static void debug_exception_enter(struct pt_regs *regs) { - preempt_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); =20 /* This code is a bit fragile. Test it. */ RCU_LOCKDEP_WARN(!rcu_is_watching(), "exception_enter didn't work"); @@ -307,7 +309,8 @@ NOKPROBE_SYMBOL(debug_exception_enter); =20 static void debug_exception_exit(struct pt_regs *regs) { - preempt_enable_no_resched(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable_no_resched(); } NOKPROBE_SYMBOL(debug_exception_exit); =20 --=20 2.54.0