Messages in this thread | | | From | Namhyung Kim <> | Subject | Re: [RFC][PATCH 0/3] ftrace: Add dynamically allocated trampolines | Date | Mon, 14 Jul 2014 16:16:08 +0900 |
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Hi Masami,
On Mon, 14 Jul 2014 10:35:21 +0900, Masami Hiramatsu wrote: > (2014/07/11 23:29), Josh Poimboeuf wrote: > [...] >> >>>From 951d2aec17885a62905df6b910dc705d99c63993 Mon Sep 17 00:00:00 2001 >> From: Josh Poimboeuf <jpoimboe@redhat.com> >> Date: Fri, 11 Jul 2014 08:58:33 -0500 >> Subject: [PATCH] x86/dumpstack: fix stack traces for generated code >> >> If a function in the stack trace is dynamically generated, for example an >> ftrace dynamically generated trampoline, print_context_stack() gets confused >> and ends up showing all the following addresses as unreliable: >> >> [ 934.546013] [<ffffffff81700312>] dump_stack+0x45/0x56 >> [ 934.546020] [<ffffffff8125f5b0>] ? meminfo_proc_open+0x30/0x30 >> [ 934.546027] [<ffffffffa080a494>] kpatch_ftrace_handler+0x14/0xf0 [kpatch] >> [ 934.546058] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0 >> [ 934.546062] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0 >> [ 934.546067] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0 >> [ 934.546071] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0 >> [ 934.546075] [<ffffffff8121423a>] ? seq_read+0x16a/0x3b0 >> [ 934.546081] [<ffffffff8125768d>] ? proc_reg_read+0x3d/0x80 >> [ 934.546088] [<ffffffff811f0668>] ? vfs_read+0x98/0x170 >> [ 934.546093] [<ffffffff811f1345>] ? SyS_read+0x55/0xd0 >> [ 934.546099] [<ffffffff81707969>] ? system_call_fastpath+0x16/0x1b >> >> Once it encounters an address which is not in the kernel's text area, it gets >> confused and stops updating the frame pointer. > > Right, this uses a module_alloc to get a memory for trampline, but > it just allocates a page in executable vmalloc area. We need a hack > in __kernel_text_address if we really want to use that. > >> The __kernel_text_address() check isn't needed when determining whether an >> address is reliable. It's only needed when deciding whether to print an >> unreliable address. > > Yeah, I guess that is for the case that the frame pointer is broken. > >> >> Here's the same stack trace with this patch: >> >> [ 1314.612287] [<ffffffff81700312>] dump_stack+0x45/0x56 >> [ 1314.612290] [<ffffffff8125f5b0>] ? meminfo_proc_open+0x30/0x30 >> [ 1314.612293] [<ffffffffa080a494>] kpatch_ftrace_handler+0x14/0xf0 [kpatch] >> [ 1314.612306] [<ffffffffa00160c4>] 0xffffffffa00160c3 > > Here, this still has a wrong entry. Maybe the trampline doesn't setup > frame pointer (bp) correctly.
Hmm.. are you saying about the hex address above? I guess it's a valid entry in the (dynamic) trampoline, but has no symbol..
> >> [ 1314.612309] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0 >> [ 1314.612311] [<ffffffff812143ae>] ? seq_read+0x2de/0x3b0 >> [ 1314.612312] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0 >> [ 1314.612314] [<ffffffff8125f5b5>] ? meminfo_proc_show+0x5/0x5e0 >> [ 1314.612315] [<ffffffff8121423a>] ? seq_read+0x16a/0x3b0
But these seem to be wrong - there're duplicate entries and they should show some of these functions (at least) correctly IMHO. I guess it's because the trampoline didn't save rbp to the stack right below the return address as dumpstack requires.
Thanks, Namhyung
>> [ 1314.612318] [<ffffffff8125768d>] proc_reg_read+0x3d/0x80 >> [ 1314.612320] [<ffffffff811f0668>] vfs_read+0x98/0x170 >> [ 1314.612322] [<ffffffff811f1345>] SyS_read+0x55/0xd0 >> [ 1314.612324] [<ffffffff81707969>] system_call_fastpath+0x16/0x1b >> --- >> arch/x86/kernel/dumpstack.c | 15 +++++++-------- >> 1 file changed, 7 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c >> index b74ebc7..db0a33c 100644 >> --- a/arch/x86/kernel/dumpstack.c >> +++ b/arch/x86/kernel/dumpstack.c >> @@ -102,14 +102,13 @@ print_context_stack(struct thread_info *tinfo, >> unsigned long addr; >> >> addr = *stack; >> - if (__kernel_text_address(addr)) { >> - if ((unsigned long) stack == bp + sizeof(long)) { >> - ops->address(data, addr, 1); >> - frame = frame->next_frame; >> - bp = (unsigned long) frame; >> - } else { >> - ops->address(data, addr, 0); >> - } >> + if ((unsigned long) stack == bp + sizeof(long)) { >> + ops->address(data, addr, 1); >> + frame = frame->next_frame; >> + bp = (unsigned long) frame; >> + print_ftrace_graph_addr(addr, data, ops, tinfo, graph); >> + } else if (__kernel_text_address(addr)) { >> + ops->address(data, addr, 0); >> print_ftrace_graph_addr(addr, data, ops, tinfo, graph); >> } >> stack++; >>
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