From patchwork Wed Mar 1 22:38:53 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Conor Dooley X-Patchwork-Id: 13156571 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 B2A5DC7EE23 for ; Wed, 1 Mar 2023 22:39:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id: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=SxX84pGqa6NNSD2Bsu6Pn6Bgz+DddMRpE9IhCkdE2W0=; b=p4gFwHyNSN8Iy+ YLAn+8Mt5wYM2sPIaion4cIJG6gHIooaN9NckiLZ/oPq4Xd/p+/bVZO/6enTbT6X7Q4h57/sZuQ9x FAoSQPfEaqRw/LFsCcKVl3bEsRG90USWWPUY1KRSJa0YNfmz5HKzF7lCEF9AUR60ukVkQzBAyIsxu 3xFG6VuHY3dofnJp9CWJQE3JhCsZo7n5XFttNEhi4Fsu0appCi0T3HKaAAKg5ha1Nf3hXiaHVgCRQ gLYPOJ5T51nTxeC1zwHbLPCYA4foXVAc32fzY++T/iFmFRdulm769MYWWxe0wrqkLfI9N0m1Lbpw5 rSHcl+Zy4Pl6x/pw/SmA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pXV6g-000CIV-I2; Wed, 01 Mar 2023 22:39:30 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pXV6d-000CHy-Eq for linux-riscv@lists.infradead.org; Wed, 01 Mar 2023 22:39:29 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 02629B81178; Wed, 1 Mar 2023 22:39:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1690CC433D2; Wed, 1 Mar 2023 22:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1677710364; bh=bVOTha/5FZGwNDfObZBUtzCQ0E5FcHiV5l1x/hNPAZc=; h=From:To:Cc:Subject:Date:From; b=INOLvCsxDfL+GyNeTU1jXNwpy+tBuorWmx88hkCoqoC5pIFZgELkl3YECR3WWc4ez vsRzL1gqjNUOl7nxC5yzMK1NkMPTjigYtvWHxAbaV4wBvK+k9eQesw94ivNHOJ6VCH /V6J17uy2veNNhLQV4zjAeiJm1esA+9cy18jZYBZEEnjETPlR+wVt8LcfM5Hp7qh5E ApmOCnKEwnNtOzDovX7yekQuNDA5vdONG5JI+JO9AA87seQ+eBObgmdd9iBPZ8Zu9p bDeaDT1uND860n4nHeJ3Wyqb0KvrK8J9z6W/mo5GDSTIeQABYfiMdKB8zSa8CA0SUG UPQUyecOcWrGw== From: Conor Dooley To: palmer@dabbelt.com Cc: conor@kernel.org, Palmer Dabbelt , linux-riscv@lists.infradead.org, Steven Rostedt , Changbin Du , Palmer Dabbelt , Conor Dooley Subject: [PATCH v4] RISC-V: Don't check text_mutex during stop_machine Date: Wed, 1 Mar 2023 22:38:53 +0000 Message-Id: <20230301223853.1444332-1-conor@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5854; i=conor.dooley@microchip.com; h=from:subject; bh=SJ05nN2Nzi0/xv73MFWwsbBRBzuLi8wuzmrgjz02YIE=; b=owGbwMvMwCFWscWwfUFT0iXG02pJDMn/L/+ynMioe/zG0Vid94pK26/PeOPAIFbJt0XgLNeLm Q5/t5d2d5SyMIhxMMiKKbIk3u5rkVr/x2WHc89bmDmsTCBDGLg4BWAiBhYM/6vcji2XUPG4rxxQ 2HVm3rNvh1/4sH84EHj4W5LV3zlBmrWMDE/Et97aqsX1rvlwWoxtgV3lxokda3ZOSRavvCDuuuK BPBsA X-Developer-Key: i=conor.dooley@microchip.com; a=openpgp; fpr=F9ECA03CF54F12CD01F1655722E2C55B37CF380C X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230301_143927_852933_5A9703CA X-CRM114-Status: GOOD ( 27.10 ) X-BeenThere: linux-riscv@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-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org From: Palmer Dabbelt We're currently using stop_machine() to update ftrace & kprobes, which means that the thread that takes text_mutex during may not be the same as the thread that eventually patches the code. This isn't actually a race because the lock is still held (preventing any other concurrent accesses) and there is only one thread running during stop_machine(), but it does trigger a lockdep failure. This patch just elides the lockdep check during stop_machine. Fixes: c15ac4fd60d5 ("riscv/ftrace: Add dynamic function tracer support") Suggested-by: Steven Rostedt Reported-by: Changbin Du Signed-off-by: Palmer Dabbelt Signed-off-by: Palmer Dabbelt Signed-off-by: Conor Dooley Reviewed-by: Changbin Du --- Changes since v3 [<20230215164317.727657-1-conor@kernel.org>]: * rename the flag to riscv_patch_in_stop_machine as it is being used for kprobes & ftrace, and just looked a bit odd. * implement Changbin's suggestion of checking the lock is held in patch_text(), rather than set the flag in callers of patch_text(). Changes since v2 [<20220322022331.32136-1-palmer@rivosinc.com>]: * rebase on riscv/for-next as it as been a year. * incorporate Changbin's suggestion that init_nop should take the lock rather than call prepare() & post_process(). Changes since v1 [<20210506071041.417854-1-palmer@dabbelt.com>]: * Use ftrace_arch_ocde_modify_{prepare,post_process}() to set the flag. I remember having a reason I wanted the function when I wrote the v1, but it's been almost a year and I forget what that was -- maybe I was just crazy, the patch was sent at midnight. * Fix DYNAMIC_FTRACE=n builds. --- arch/riscv/include/asm/ftrace.h | 7 +++++++ arch/riscv/kernel/ftrace.c | 15 +++++++++++++-- arch/riscv/kernel/patch.c | 26 +++++++++++++++++++++++--- 3 files changed, 43 insertions(+), 5 deletions(-) diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h index 9e73922e1e2e..41e0f4aa5243 100644 --- a/arch/riscv/include/asm/ftrace.h +++ b/arch/riscv/include/asm/ftrace.h @@ -107,8 +107,15 @@ do { \ struct dyn_ftrace; int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); #define ftrace_init_nop ftrace_init_nop +extern int riscv_patch_in_stop_machine; #endif +#else /* CONFIG_DYNAMIC_FTRACE */ + +#ifndef __ASSEMBLY__ +#define riscv_patch_in_stop_machine 0 #endif +#endif /* CONFIG_DYNAMIC_FTRACE */ + #endif /* _ASM_RISCV_FTRACE_H */ diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c index 5bff37af4770..00cb8d51a0ec 100644 --- a/arch/riscv/kernel/ftrace.c +++ b/arch/riscv/kernel/ftrace.c @@ -11,14 +11,25 @@ #include #include +int riscv_patch_in_stop_machine; + #ifdef CONFIG_DYNAMIC_FTRACE void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) { mutex_lock(&text_mutex); + + /* + * The code sequences we use for ftrace can't be patched while the + * kernel is running, so we need to use stop_machine() to modify them + * for now. This doesn't play nice with text_mutex, we use this flag + * to elide the check. + */ + riscv_patch_in_stop_machine = true; } void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) { + riscv_patch_in_stop_machine = false; mutex_unlock(&text_mutex); } @@ -107,9 +118,9 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) { int out; - ftrace_arch_code_modify_prepare(); + mutex_lock(&text_mutex); out = ftrace_make_nop(mod, rec, MCOUNT_ADDR); - ftrace_arch_code_modify_post_process(); + mutex_unlock(&text_mutex); return out; } diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c index 765004b60513..eef1243f6844 100644 --- a/arch/riscv/kernel/patch.c +++ b/arch/riscv/kernel/patch.c @@ -11,6 +11,7 @@ #include #include #include +#include #include struct patch_insn { @@ -59,8 +60,15 @@ static int patch_insn_write(void *addr, const void *insn, size_t len) * Before reaching here, it was expected to lock the text_mutex * already, so we don't need to give another lock here and could * ensure that it was safe between each cores. + * + * We're currently using stop_machine() for ftrace & kprobes, and while + * that ensures text_mutex is held before installing the mappings it + * does not ensure text_mutex is held by the calling thread. That's + * safe but triggers a lockdep failure, so just elide it for that + * specific case. */ - lockdep_assert_held(&text_mutex); + if (!riscv_patch_in_stop_machine) + lockdep_assert_held(&text_mutex); if (across_pages) patch_map(addr + len, FIX_TEXT_POKE1); @@ -121,13 +129,25 @@ NOKPROBE_SYMBOL(patch_text_cb); int patch_text(void *addr, u32 insn) { + int ret; struct patch_insn patch = { .addr = addr, .insn = insn, .cpu_count = ATOMIC_INIT(0), }; - return stop_machine_cpuslocked(patch_text_cb, - &patch, cpu_online_mask); + /* + * kprobes takes text_mutex, before calling patch_text(), but as we call + * calls stop_machine(), the lockdep assertion in patch_insn_write() + * gets confused by the context in which the lock is taken. + * Instead, ensure the lock is held before calling stop_machine(), and + * set riscv_patch_in_stop_machine to skip the check in + * patch_insn_write(). + */ + lockdep_assert_held(&text_mutex); + riscv_patch_in_stop_machine = true; + ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask); + riscv_patch_in_stop_machine = false; + return ret; } NOKPROBE_SYMBOL(patch_text);