On Fri, Jul 11, 2014 at 03:24:28PM +0200, Jiri Kosina wrote: > On Fri, 11 Jul 2014, Masami Hiramatsu wrote: > > > >> I did some testing with kpatch and I found one minor issue. The > > >> dynamically > > >> allocated trampoline seems to confuse dump_stack() somewhat. > > >> > > >> I added a dump_stack() call in my ftrace_ops callback function > > >> (kpatch_ftrace_handler) which had a filter on meminfo_proc_show(). > > > > > > Interesting. Are you using dwarf2 unwinder for stack dumping by any > > > chance? It seems to get things right here. Will look into it more > > > tomorrow. > > > > Hmm, can dwarf2 unwinder work on the trampoline method? Since the > > trampoline just a copy of instructions which will not have CFI(which is > > stored in dwarf section), I guess it may not work... Frame pointer (push > > bp and save sp to bp on the entry) can work anyway. > > That was exactly my idea and that's why I asked, thanks for confirming. > > I am afraid we'll have to declare dynamic trampolines incompatible with > drawf2 stack dumping.
In this case, the problem wasn't related to DWARF, because dump_stack() uses the frame pointer to unwind the stack. I was able to fix the problem with the following patch. --- >From 951d2aec17885a62905df6b910dc705d99c63993 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf <jpoim...@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. 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. 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 [ 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 [ 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++; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/