From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5D80ECD4F54 for ; Tue, 19 May 2026 22:25:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:content-type: Content-Transfer-Encoding:MIME-Version:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender :Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=vAB44BGqZ+fuUDNGrRoAE7PFPdrgJUI60GqrOp9DD1k=; b=vInYYq+UlujnaWjs53ZzzCP6dI ohr9/K00NYf0RKMKZtrfaQUTmr70y/tR6FP1pXmdWecWzIPngHOHicGVDr99aQq8fVmSGI5nCqh6y sacmBft/P4EITvVR4pEPA4dPZ7Dn9Wezhldnm9mPCLKRhoM7hdITC5rGzvdy91EpdfA99Opcs3swV PVMn7gL7J0VOJDnHKkXm0UV0I9NcgCGLlfsNyjtAXPSf8Oy0PSfbREYDlig8tR5QG84GOUWzhHWSl I0QN5YMMPOleMGMUoDHXwzePVp4JngprYaDSiBjFOrMRNKLOUXzWlloZPOa9eHwWdHO6g4BoV9q9y wvOeiesA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPSsr-00000002wZu-0A83; Tue, 19 May 2026 22:25:53 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wPSso-00000002wZ1-1f5q for linux-arm-kernel@lists.infradead.org; Tue, 19 May 2026 22:25:51 +0000 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-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=vAB44BGqZ+fuUDNGrRoAE7PFPdrgJUI60GqrOp9DD1k=; b=PukbmEN5i9YisSyy3uwhoK/gMORZ1FKwwpIf3benZA2uAylsaOm8Bl0Z6WFERAvYKyKdEj pQL2ty6sYTW2wj+BQzDJGJ1zb+khFmlSUA/rvRE+12d72BK9KwP9s7gKpPk6mhayBy+cYF qru/tG04pJ4+cFj0KUR9blrCvSxMA2w= 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> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-MFC-PROC-ID: qGj4UvsTlsFbgpkeT9yQldyDQwbbMNaTvDCmt8E4V7U_1779229540 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260519_152550_508168_A130E3BE X-CRM114-Status: GOOD ( 11.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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/spinlock_rt.c:48 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 15255, name: gdb_app 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-common.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) } /* - * 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(); /* 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); 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); -- 2.54.0