Matt, This bug looks very similar to what you were hitting with the function profiler. Can you apply this patch and see if it fixes the issue for you.
Thanks! -- Steve On Fri, 13 May 2016 22:53:43 +0900 Namhyung Kim <[email protected]> wrote: > On my system, simply enabling and disabling function graph tracer can > crash the kernel. I don't know how it worked until now. > > The ftrace_disable_ftrace_graph_caller() modifies jmp instruction at > ftrace_graph_call assuming it's a 5 bytes near jmp (e9 <offset>). > However it's a short jmp consisting of 2 bytes only (eb <offset>). And > ftrace_stub() is located just below the ftrace_graph_caller so > modification above breaks the instruction resulting in kernel oops on > the ftrace_stub() with the invalid opcode like below: > > # cd /sys/kernel/trace > # echo function_graph > current_tracer > # echo nop > current_tracer > > [ 78.122055] invalid opcode: 0000 [#1] SMP > [ 78.125125] Modules linked in: x86_pkg_temp_thermal kvm_intel kvm > irqbypass crc32c_intel pcspkr iwldvm iwlwifi > [ 78.128241] CPU: 2 PID: 17 Comm: migration/2 Not tainted 4.6.0-rc4+ #36 > [ 78.131310] Hardware name: LENOVO 4286A74/4286A74, BIOS 8DET56WW (1.26 ) > 12/01/2011 > [ 78.134369] task: ffff88040bec4240 ti: ffff88040bee4000 task.ti: > ffff88040bee4000 > [ 78.137412] RIP: 0010:[<ffffffff818939a8>] [<ffffffff818939a8>] > ftrace_stub+0x0/0x8 > [ 78.140477] RSP: 0018:ffff88040bee7e48 EFLAGS: 00010246 > [ 78.143489] RAX: ffff88040bec4240 RBX: ffffffff8107a7b0 RCX: > 000000000000001f > [ 78.146512] RDX: 0000000000000000 RSI: ffff88041e2929d8 RDI: > ffff88040bee7e50 > [ 78.149581] RBP: ffff88040bee7e80 R08: ffff88040bee4000 R09: > 0000000000000000 > [ 78.152647] R10: 00000000000318b7 R11: ffff8800d661f800 R12: > ffff88040d8011b0 > [ 78.155679] R13: ffffffff81e43620 R14: ffff88040bda8588 R15: > ffffffff81e503e0 > [ 78.158675] FS: 0000000000000000(0000) GS:ffff88041e280000(0000) > knlGS:0000000000000000 > [ 78.161699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 78.164690] CR2: 00007fadb22dde1d CR3: 00000000d5ce2000 CR4: > 00000000000406e0 > [ 78.167691] Stack: > [ 78.170658] ffffffff8110b3ee ffffffff8188de90 00000009161d55f6 > 00000012306fc2e4 > [ 78.173710] 0000000000000000 ffff880400000000 ffff88040bec4240 > ffff88040bee7ec8 > [ 78.176783] ffffffff81893bbd 0000000000000000 ffff88040bec4240 > ffffffff81893ba8 > [ 78.179863] Call Trace: > [ 78.182853] [<ffffffff8110b3ee>] ? ftrace_return_to_handler+0x8e/0x100 > [ 78.185909] [<ffffffff8188de90>] ? __schedule+0xae0/0xae0 > [ 78.188941] [<ffffffff81893bbd>] return_to_handler+0x15/0x27 > [ 78.192001] [<ffffffff81893ba8>] ? ftrace_graph_caller+0xa8/0xa8 > [ 78.195091] [<ffffffff8107a6f0>] ? sort_range+0x30/0x30 > [ 78.198138] [<ffffffff810778a9>] kthread+0xc9/0xe0 > [ 78.201143] [<ffffffff81891a12>] ret_from_fork+0x22/0x40 > [ 78.204138] [<ffffffff810777e0>] ? kthread_worker_fn+0x170/0x170 > [ 78.207129] Code: 8b 44 24 48 48 8b 7c 24 70 48 8b 74 24 68 48 8b 54 24 > 60 > 48 8b 4c 24 58 48 8b 44 24 50 48 8b 6c 24 20 48 81 c4 > d0 > 00 00 00 e9 fd <ff> ff ff 80 00 00 00 00 9c 55 ff 74 > 24 18 > 55 48 89 e5 ff 74 24 > [ 78.213997] RIP [<ffffffff818939a8>] ftrace_stub+0x0/0x8 > [ 78.217190] RSP <ffff88040bee7e48> > [ 78.220374] ---[ end trace 0af2f0d9f7301011 ]--- > > Looking at the code dump, the ftrace_stub instruction was overwritten as > <ff>. Below is disassembly output of related code. > > $ objdump -d --start-address=0xffffffff818939a6 > --stop-address=0xffffffff818939b0 vmlinux > > vmlinux: file format elf64-x86-64 > > Disassembly of section .text: > > ffffffff818939a6 <ftrace_epilogue>: > ffffffff818939a6: eb 00 jmp ffffffff818939a8 > <ftrace_stub> > > ffffffff818939a8 <ftrace_stub>: > ffffffff818939a8: c3 retq > ffffffff818939a9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) > > As you can see ftrace_epilogue (same as ftrace_graph_caller) is 2 byte > ahead of ftrace_stub. And it's replaced by a jump to ftrace_stub() by > ftrace_disable_ftrace_graph_caller: "e9 <0xfffffffd>". Pads 3 bytes > after ftrace_epilogue to prevent ftrace_stub from being overwritten. > > Signed-off-by: Namhyung Kim <[email protected]> > --- > arch/x86/kernel/mcount_64.S | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S > index ed48a9f465f8..0e6af57a713a 100644 > --- a/arch/x86/kernel/mcount_64.S > +++ b/arch/x86/kernel/mcount_64.S > @@ -180,6 +180,15 @@ GLOBAL(ftrace_epilogue) > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > GLOBAL(ftrace_graph_call) > jmp ftrace_stub > + /* > + * The above jmp is generated as a short jump which occupies 2 bytes > + * but ftrace_enable/disable_ftrace_graph_caller() assumes it's a > + * near jump which occupies 5 bytes so breaks ftrace_stub() below. > + * Add 3 bytes padding to avoid that. > + */ > + nop > + nop > + nop > #endif > > GLOBAL(ftrace_stub)
