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Message-Id: <4a92b0bf5ee602de6463057e5d98d20b4d4f2bcd.1503924827.git.panand@redhat.com>
Date: Mon, 28 Aug 2017 18:23:54 +0530
From: Pratyush Anand <panand@...hat.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Pratyush Anand <panand@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: fix unwind_frame() for filtered out fn via set_graph_notrace
Testcase:
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
PANIC: "Unable to handle kernel paging request at virtual address
ffff801bcbde7000"
vmcore analysis:
1)
crash> bt
PID: 1561 TASK: ffff8003cb7e4000 CPU: 0 COMMAND: "ps"
#0 [ffff8003c4ff77b0] crash_kexec at ffff00000816b9b8
#1 [ffff8003c4ff77e0] die at ffff000008088b34
#2 [ffff8003c4ff7820] __do_kernel_fault at ffff00000809b830
#3 [ffff8003c4ff7850] do_bad_area at ffff000008098b90
#4 [ffff8003c4ff7880] do_translation_fault at ffff0000087c6cdc
#5 [ffff8003c4ff78b0] do_mem_abort at ffff000008081334
#6 [ffff8003c4ff7ab0] el1_ia at ffff000008082cc0
PC: ffff00000808811c [unwind_frame+300]
LR: ffff0000080858a8 [get_wchan+212]
SP: ffff8003c4ff7ab0 PSTATE: 60000145
X29: ffff8003c4ff7ab0 X28: 0000000000000001 X27: 0000000000000000
X26: 0000000000000000 X25: 0000000000000000 X24: 0000000000000000
X23: ffff8003c1c20000 X22: ffff000008c73000 X21: ffff8003c1c1c000
X20: 000000000000000f X19: ffff8003c1bc7000 X18: 0000000000000010
X17: 0000000000000000 X16: 0000000000000001 X15: ffffffffffffffed
X14: 0000000000000010 X13: ffffffffffffffff X12: 0000000000000004
X11: 0000000000000000 X10: 0000000002dd14c0 X9: 1999999999999999
X8: 000000000000003f X7: 00008003f71b0000 X6: 0000000000000018
X5: 0000000000000000 X4: ffff8003c1c1fd20 X3: ffff8003c1c1fd10
X2: 00000017ffe80000 X1: ffff8003c4ff7af8 X0: ffff8003cbf67000
#7 [ffff8003c4ff7b20] do_task_stat at ffff000008304f0c
#8 [ffff8003c4ff7c60] proc_tgid_stat at ffff000008305b48
#9 [ffff8003c4ff7ca0] proc_single_show at ffff0000082fdd10
#10 [ffff8003c4ff7ce0] seq_read at ffff0000082b27bc
#11 [ffff8003c4ff7d70] __vfs_read at ffff000008289e54
#12 [ffff8003c4ff7e30] vfs_read at ffff00000828b14c
#13 [ffff8003c4ff7e70] sys_read at ffff00000828c2d0
#14 [ffff8003c4ff7ed0] __sys_trace at ffff00000808349c
PC: 00000006 LR: 00000000 SP: ffffffffffffffed PSTATE: 0000003f
X12: 00000010 X11: ffffffffffffffff X10: 00000004 X9: ffff7febe8d0
X8: 00000000 X7: 1999999999999999 X6: 0000003f X5: 0000000c
X4: ffff7fce9c78 X3: 0000000c X2: 00000000 X1: 00000000
X0: 00000400
(2) Instruction at ffff00000808811c caused IA/DA.
crash> dis -l ffff000008088108 6
/usr/src/debug/xxxxxxxxxxxx/xxxxxxxxxx/arch/arm64/kernel/stacktrace.c:
84
0xffff000008088108 <unwind_frame+280>: ldr w2, [x1,#24]
0xffff00000808810c <unwind_frame+284>: sub w6, w2, #0x1
0xffff000008088110 <unwind_frame+288>: str w6, [x1,#24]
0xffff000008088114 <unwind_frame+292>: mov w6, #0x18 // #24
0xffff000008088118 <unwind_frame+296>: umull x2, w2, w6
0xffff00000808811c <unwind_frame+300>: ldr x0, [x0,x2]
Corresponding c statement is
frame->pc = tsk->ret_stack[frame->graph--].ret;
(3) So, it caused data abort while executing
0xffff00000808811c <unwind_frame+300>: ldr x0, [x0,x2]
x0 + x2 = ffff8003cbf67000 + 00000017ffe80000 = ffff801bcbde7000
Access of ffff801bcbde7000 resulted in "Unable to handle kernel paging
request"
from above data: frame->graph = task->curr_ret_stack which should be,
x2 / 0x18 = FFFF0000, which is -FTRACE_NOTRACE_DEPTH.
OK, so problem is here:
do_task_stat() calls get_wchan(). Here p->curr_ret_stack is
-FTRACE_NOTRACE_DEPTH in the failed case. It means, when do_task_stat()
has been called for task A (ps in this case) on CPUm,task A was in mid
of execution on CPUn, and was in the mid of mcount() execution where
curr_ret_stack had been decremented in ftrace_push_return_trace() for
hitting schedule() function, but it was yet to be incremented in
ftrace_return_to_handler().
Similar problem we can have with calling of walk_stackframe() from
save_stack_trace_tsk() or dump_backtrace().
This patch fixes unwind_frame() to not to manipulate frame->pc for
function graph tracer if the function has been marked in
set_graph_notrace.
This patch fixes: 20380bb390a4 (arm64: ftrace: fix a stack tracer's
output under function graph tracer)
Signed-off-by: Pratyush Anand <panand@...hat.com>
---
arch/arm64/kernel/stacktrace.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 09d37d66b630..e79035d673b3 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -74,7 +74,8 @@ 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)) {
+ (frame->pc == (unsigned long)return_to_handler) &&
+ (frame->graph > -1)) {
/*
* This is a case where function graph tracer has
* modified a return address (LR) in a stack frame
--
2.9.4
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