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Message-Id: <20260130015740.212343-1-imntjempty@163.com>
Date: Fri, 30 Jan 2026 01:57:40 +0000
From: "jempty.liang" <imntjempty@....com>
To: rostedt@...dmis.org,
mhiramat@...nel.org,
mark.rutland@....com,
mathieu.desnoyers@...icios.com
Cc: linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org,
"jempty.liang" <imntjempty@....com>
Subject: [PATCH] tracing: Fix duration calculation bug (rettime - calltime) on ARM architecture
This issue is reproducible on the QEMU vexpress-a9 platform with the
following steps:
Step 1: Launch the QEMU vexpress-a9 VM
~# qemu-system-arm -M vexpress-a9 -smp 1 -m 256 -kernel zImage -dtb \
vexpress-v2p-ca9.dtb -drive file=rootfs.ext2,if=sd,format=raw \
-append "console=ttyAMA0,115200 rootwait" -net nic,model=lan9118 \
-net user -serial stdio
Step 2: Capture and view the trace with trace-cmd
~# trace-cmd record -p function_graph -g do_open_execat \
--max-graph-depth 1 dd if=/dev/zero of=/tmp/1.bin \
bs=1M count=1
~# trace-cmd report
Step 3: Observed behavior
Before:
dd-89 ... 5.764026: funcgraph_entry: $ 2757369004 us | do_open_execat()
dd-89 ... 5.765222: funcgraph_entry: $ 2034790547 us | do_open_execat();
After:
dd-91 ... 891.945577: funcgraph_entry: ! 185.542 us | do_open_execat();
dd-91 ... 891.946840: funcgraph_entry: + 98.625 us | do_open_execat();
Signed-off-by: jempty.liang <imntjempty@....com>
---
include/linux/ftrace.h | 2 ++
kernel/trace/trace_entries.h | 8 ++++----
kernel/trace/trace_functions_graph.c | 19 +++++++++----------
3 files changed, 15 insertions(+), 14 deletions(-)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a3a8989e3268..52727a342273 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1191,6 +1191,8 @@ struct ftrace_graph_ret {
int depth;
/* Number of functions that overran the depth limit for current task */
unsigned int overrun;
+ unsigned long long calltime;
+ unsigned long long rettime;
} __packed;
struct fgraph_ops;
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index f6a8d29c0d76..362a757e65a2 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -127,8 +127,8 @@ FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
__field_packed( unsigned long, ret, retval )
__field_packed( unsigned int, ret, depth )
__field_packed( unsigned int, ret, overrun )
- __field(unsigned long long, calltime )
- __field(unsigned long long, rettime )
+ __field_packed(unsigned long long, ret, calltime)
+ __field_packed(unsigned long long, ret, rettime)
),
F_printk("<-- %ps (%u) (start: %llx end: %llx) over: %u retval: %lx",
@@ -149,8 +149,8 @@ FTRACE_ENTRY_PACKED(funcgraph_exit, ftrace_graph_ret_entry,
__field_packed( unsigned long, ret, func )
__field_packed( unsigned int, ret, depth )
__field_packed( unsigned int, ret, overrun )
- __field(unsigned long long, calltime )
- __field(unsigned long long, rettime )
+ __field_packed(unsigned long long, ret, calltime)
+ __field_packed(unsigned long long, ret, rettime)
),
F_printk("<-- %ps (%u) (start: %llx end: %llx) over: %u",
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 1de6f1573621..5798aeb31f05 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -317,6 +317,8 @@ __trace_graph_function(struct trace_array *tr,
struct ftrace_graph_ret ret = {
.func = ip,
.depth = 0,
+ .calltime = time,
+ .rettime = time,
};
__trace_graph_entry(tr, &ent, trace_ctx);
@@ -346,8 +348,8 @@ void __trace_graph_return(struct trace_array *tr,
return;
entry = ring_buffer_event_data(event);
entry->ret = *trace;
- entry->calltime = calltime;
- entry->rettime = rettime;
+ entry->ret.calltime = calltime;
+ entry->ret.rettime = rettime;
trace_buffer_unlock_commit_nostack(buffer, event);
}
@@ -372,10 +374,9 @@ void trace_graph_return(struct ftrace_graph_ret *trace,
struct trace_array *tr = gops->private;
struct fgraph_times *ftimes;
unsigned int trace_ctx;
- u64 calltime, rettime;
int size;
- rettime = trace_clock_local();
+ trace->rettime = trace_clock_local();
ftrace_graph_addr_finish(gops, trace);
@@ -390,10 +391,10 @@ void trace_graph_return(struct ftrace_graph_ret *trace,
handle_nosleeptime(tr, trace, ftimes, size);
- calltime = ftimes->calltime;
+ trace->calltime = ftimes->calltime;
trace_ctx = tracing_gen_ctx();
- __trace_graph_return(tr, trace, trace_ctx, calltime, rettime);
+ __trace_graph_return(tr, trace, trace_ctx, trace->calltime, trace->rettime);
}
static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
@@ -956,7 +957,7 @@ print_graph_entry_leaf(struct trace_iterator *iter,
graph_ret = &ret_entry->ret;
call = &entry->graph_ent;
- duration = ret_entry->rettime - ret_entry->calltime;
+ duration = graph_ret->rettime - graph_ret->calltime;
if (data) {
struct fgraph_cpu_data *cpu_data;
@@ -1280,9 +1281,7 @@ print_graph_return(struct ftrace_graph_ret_entry *retentry, struct trace_seq *s,
u32 flags)
{
struct ftrace_graph_ret *trace = &retentry->ret;
- u64 calltime = retentry->calltime;
- u64 rettime = retentry->rettime;
- unsigned long long duration = rettime - calltime;
+ unsigned long long duration = trace->rettime - trace->calltime;
struct fgraph_data *data = iter->private;
struct trace_array *tr = iter->tr;
unsigned long func;
--
2.25.1
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