From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751237AbdIAFtY (ORCPT ); Fri, 1 Sep 2017 01:49:24 -0400 Received: from mail-pg0-f47.google.com ([74.125.83.47]:38841 "EHLO mail-pg0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750753AbdIAFtW (ORCPT ); Fri, 1 Sep 2017 01:49:22 -0400 X-Google-Smtp-Source: ADKCNb7kbWATOsmHwp//5Fqr6NCI/7DQiZyxsmzXuSVtaliOPVl0vXFrep4UTbwiaESdzWsV+CWSIg== From: Pratyush Anand To: linux-arm-kernel@lists.infradead.org Cc: james.morse@arm.com, Pratyush Anand , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org Subject: [PATCH v2] arm64: fix unwind_frame() for filtered out fn for function graph tracing Date: Fri, 1 Sep 2017 11:18:47 +0530 Message-Id: <3c175a7a1f7c2e08098f6d5e84dc247ce94846d2.1504244801.git.panand@redhat.com> X-Mailer: git-send-email 2.9.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org do_task_stat() calls get_wchan(), which further does unbind_frame(). unbind_frame() restores frame->pc to original value in case function graph tracer has modified a return address (LR) in a stack frame to hook a function return. However, if function graph tracer has hit a filtered function, then we can't unwind it as ftrace_push_return_trace() has biased the index(frame->graph) with a 'huge negative' offset(-FTRACE_NOTRACE_DEPTH). Moreover, arm64 stack walker defines index(frame->graph) as unsigned int, which can not compare a -ve number. Similar problem we can have with calling of walk_stackframe() from save_stack_trace_tsk() or dump_backtrace(). This patch fixes unwind_frame() to test the index for -ve value and restore index accordingly before we can restore frame->pc. Reproducer: cd /sys/kernel/debug/tracing/ echo schedule > set_graph_notrace echo 1 > options/display-graph echo wakeup > current_tracer ps -ef | grep -i agent Above commands result in: Unable to handle kernel paging request at virtual address ffff801bd3d1e000 pgd = ffff8003cbe97c00 [ffff801bd3d1e000] *pgd=0000000000000000, *pud=0000000000000000 Internal error: Oops: 96000006 [#1] SMP [...] CPU: 5 PID: 11696 Comm: ps Not tainted 4.11.0+ #33 [...] task: ffff8003c21ba000 task.stack: ffff8003cc6c0000 PC is at unwind_frame+0x12c/0x180 LR is at get_wchan+0xd4/0x134 pc : [] lr : [] pstate: 60000145 sp : ffff8003cc6c3ab0 x29: ffff8003cc6c3ab0 x28: 0000000000000001 x27: 0000000000000026 x26: 0000000000000026 x25: 00000000000012d8 x24: 0000000000000000 x23: ffff8003c1c04000 x22: ffff000008c83000 x21: ffff8003c1c00000 x20: 000000000000000f x19: ffff8003c1bc0000 x18: 0000fffffc593690 x17: 0000000000000000 x16: 0000000000000001 x15: 0000b855670e2b60 x14: 0003e97f22cf1d0f x13: 0000000000000001 x12: 0000000000000000 x11: 00000000e8f4883e x10: 0000000154f47ec8 x9 : 0000000070f367c0 x8 : 0000000000000000 x7 : 00008003f7290000 x6 : 0000000000000018 x5 : 0000000000000000 x4 : ffff8003c1c03cb0 x3 : ffff8003c1c03ca0 x2 : 00000017ffe80000 x1 : ffff8003cc6c3af8 x0 : ffff8003d3e9e000 Process ps (pid: 11696, stack limit = 0xffff8003cc6c0000) Stack: (0xffff8003cc6c3ab0 to 0xffff8003cc6c4000) [...] [] unwind_frame+0x12c/0x180 [] do_task_stat+0x864/0x870 [] proc_tgid_stat+0x3c/0x48 [] proc_single_show+0x5c/0xb8 [] seq_read+0x160/0x414 [] __vfs_read+0x58/0x164 [] vfs_read+0x88/0x144 [] SyS_read+0x60/0xc0 [] __sys_trace_return+0x0/0x4 fixes: 20380bb390a4 (arm64: ftrace: fix a stack tracer's output under function graph tracer) Signed-off-by: Pratyush Anand --- v1 -> v2: - improved commit log - now index is restored and thereafter frame->pc as well. arch/arm64/include/asm/stacktrace.h | 2 +- arch/arm64/kernel/stacktrace.c | 3 +++ 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h index 5b6eafccc5d8..816db5b9b874 100644 --- a/arch/arm64/include/asm/stacktrace.h +++ b/arch/arm64/include/asm/stacktrace.h @@ -23,7 +23,7 @@ struct stackframe { unsigned long sp; unsigned long pc; #ifdef CONFIG_FUNCTION_GRAPH_TRACER - unsigned int graph; + int graph; #endif }; diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index 09d37d66b630..4c47147d0554 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -75,6 +75,9 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) #ifdef CONFIG_FUNCTION_GRAPH_TRACER if (tsk->ret_stack && (frame->pc == (unsigned long)return_to_handler)) { + if (frame->graph < 0) + frame->graph += FTRACE_NOTRACE_DEPTH; + /* * This is a case where function graph tracer has * modified a return address (LR) in a stack frame -- 2.9.4