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 X-Spam-Level: X-Spam-Status: No, score=-24.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B1D4CC432BE for ; Thu, 29 Jul 2021 13:55:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90AB160ED4 for ; Thu, 29 Jul 2021 13:55:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237831AbhG2NzE (ORCPT ); Thu, 29 Jul 2021 09:55:04 -0400 Received: from linux.microsoft.com ([13.77.154.182]:36586 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237656AbhG2NzD (ORCPT ); Thu, 29 Jul 2021 09:55:03 -0400 Received: from [192.168.254.32] (unknown [47.187.212.181]) by linux.microsoft.com (Postfix) with ESMTPSA id 2FA3620B36E8; Thu, 29 Jul 2021 06:54:59 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 2FA3620B36E8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1627566900; bh=0nVaqk7iajeUlBqRCzVPHIC889cPZdErmHJQuZLPtCA=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=PTI2c75KrM3L7fDS7rcylvLg2/9jOmXv9PVjoeE87Ro90eckniXpVrMm49gQ2a/9z J7xxBieYPorZTO22QX3A7SxCQ8Ob4hptli1yxhMn0raRRcWgpYOhX0nZh6TvxKdDjX oBh6YJo7HZ+Mimo/QsDbLR1InQhGmm3fbv5pZJvE= Subject: Re: [RFC PATCH v6 1/3] arm64: Improve the unwinder return value To: Mark Rutland Cc: broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, jthierry@redhat.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <3f2aab69a35c243c5e97f47c4ad84046355f5b90> <20210630223356.58714-1-madvenka@linux.microsoft.com> <20210630223356.58714-2-madvenka@linux.microsoft.com> <20210728165635.GA47345@C02TD0UTHF1T.local> From: "Madhavan T. Venkataraman" Message-ID: <52686cb6-573c-03ca-06c2-67ae07c91243@linux.microsoft.com> Date: Thu, 29 Jul 2021 08:54:58 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210728165635.GA47345@C02TD0UTHF1T.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks for the review. Responses inline... On 7/28/21 11:56 AM, Mark Rutland wrote: > On Wed, Jun 30, 2021 at 05:33:54PM -0500, madvenka@linux.microsoft.com wrote: >> From: "Madhavan T. Venkataraman" >> >> Currently, the unwinder returns a tri-state return value: >> >> 0 means "continue with the unwind" >> -ENOENT means "successful termination of the stack trace" >> -EINVAL means "fatal error, abort the stack trace" >> >> This is confusing. To fix this, define an enumeration of different return >> codes to make it clear. Handle the return codes in all of the unwind >> consumers. > > I agree the tri-state is confusing, and I also generally agree that > enums are preferabel to a set of error codes. However, I don't think > this is quite the right abstraction; more on that below. > OK. >> >> Signed-off-by: Madhavan T. Venkataraman >> --- >> arch/arm64/include/asm/stacktrace.h | 14 ++++++-- >> arch/arm64/kernel/perf_callchain.c | 5 ++- >> arch/arm64/kernel/process.c | 8 +++-- >> arch/arm64/kernel/return_address.c | 10 ++++-- >> arch/arm64/kernel/stacktrace.c | 53 ++++++++++++++++------------- >> arch/arm64/kernel/time.c | 9 +++-- >> 6 files changed, 64 insertions(+), 35 deletions(-) >> >> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h >> index eb29b1fe8255..6fcd58553fb1 100644 >> --- a/arch/arm64/include/asm/stacktrace.h >> +++ b/arch/arm64/include/asm/stacktrace.h >> @@ -30,6 +30,12 @@ struct stack_info { >> enum stack_type type; >> }; >> >> +enum unwind_rc { >> + UNWIND_CONTINUE, /* No errors encountered */ >> + UNWIND_ABORT, /* Fatal errors encountered */ >> + UNWIND_FINISH, /* End of stack reached successfully */ >> +}; > > Generally, there are a bunch of properties we might need to check for an > unwind step relating to reliabiltiy (e.g. as you add > UNWIND_CONTINUE_WITH_RISK in the next patch), and I'd prefer that we > check those properties on the struct stackframe, and simplify > unwind_frame() to return a bool. > > Something akin to the x86 unwinders, where the main loop looks like: > > for (unwind_start(&state, ...); > !unwind_done(&state) && !unwind_error(&state); > unwind_next_frame(&state) { > ... > } > > That way we don't have to grow the enum to handle every variation that > we can think of, and it's simple enough for users to check the > properties with the helpers. > I can do that. >> + >> /* >> * A snapshot of a frame record or fp/lr register values, along with some >> * accounting information necessary for robust unwinding. >> @@ -61,7 +67,8 @@ struct stackframe { >> #endif >> }; >> >> -extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame); >> +extern enum unwind_rc unwind_frame(struct task_struct *tsk, >> + struct stackframe *frame); >> extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame, >> bool (*fn)(void *, unsigned long), void *data); >> extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk, >> @@ -148,8 +155,8 @@ static inline bool on_accessible_stack(const struct task_struct *tsk, >> return false; >> } >> >> -static inline void start_backtrace(struct stackframe *frame, >> - unsigned long fp, unsigned long pc) >> +static inline enum unwind_rc start_backtrace(struct stackframe *frame, >> + unsigned long fp, unsigned long pc) >> { >> frame->fp = fp; >> frame->pc = pc; >> @@ -169,6 +176,7 @@ static inline void start_backtrace(struct stackframe *frame, >> bitmap_zero(frame->stacks_done, __NR_STACK_TYPES); >> frame->prev_fp = 0; >> frame->prev_type = STACK_TYPE_UNKNOWN; >> + return UNWIND_CONTINUE; >> } >> >> #endif /* __ASM_STACKTRACE_H */ >> diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c >> index 88ff471b0bce..f459208149ae 100644 >> --- a/arch/arm64/kernel/perf_callchain.c >> +++ b/arch/arm64/kernel/perf_callchain.c >> @@ -148,13 +148,16 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, >> struct pt_regs *regs) >> { >> struct stackframe frame; >> + enum unwind_rc rc; >> >> if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) { >> /* We don't support guest os callchain now */ >> return; >> } >> >> - start_backtrace(&frame, regs->regs[29], regs->pc); >> + rc = start_backtrace(&frame, regs->regs[29], regs->pc); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return; >> walk_stackframe(current, &frame, callchain_trace, entry); > > As a first step, could we convert this over to arch_stack_walk()? > OK. >> } >> >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >> index 6e60aa3b5ea9..e9c763b44fd4 100644 >> --- a/arch/arm64/kernel/process.c >> +++ b/arch/arm64/kernel/process.c >> @@ -573,6 +573,7 @@ unsigned long get_wchan(struct task_struct *p) >> struct stackframe frame; >> unsigned long stack_page, ret = 0; >> int count = 0; >> + enum unwind_rc rc; >> if (!p || p == current || p->state == TASK_RUNNING) >> return 0; >> >> @@ -580,10 +581,13 @@ unsigned long get_wchan(struct task_struct *p) >> if (!stack_page) >> return 0; >> >> - start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p)); >> + rc = start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p)); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return 0; >> >> do { >> - if (unwind_frame(p, &frame)) >> + rc = unwind_frame(p, &frame); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> goto out; >> if (!in_sched_functions(frame.pc)) { >> ret = frame.pc; > > Likewise, can we convert this to use arch_stack_walk()? > OK. >> diff --git a/arch/arm64/kernel/return_address.c b/arch/arm64/kernel/return_address.c >> index a6d18755652f..1224e043e98f 100644 >> --- a/arch/arm64/kernel/return_address.c >> +++ b/arch/arm64/kernel/return_address.c >> @@ -36,13 +36,17 @@ void *return_address(unsigned int level) >> { >> struct return_address_data data; >> struct stackframe frame; >> + enum unwind_rc rc; >> >> data.level = level + 2; >> data.addr = NULL; >> >> - start_backtrace(&frame, >> - (unsigned long)__builtin_frame_address(0), >> - (unsigned long)return_address); >> + rc = start_backtrace(&frame, >> + (unsigned long)__builtin_frame_address(0), >> + (unsigned long)return_address); >> + if (rc == UNWIND_FINISH || rc == UNWIND_ABORT) >> + return NULL; >> + >> walk_stackframe(current, &frame, save_return_addr, &data); > > Likewise, can we convert this to use arch_stack_walk()? > OK. Thanks. Madhavan