kernel/trace/trace_functions_graph.c | 6 ++++++ 1 file changed, 6 insertions(+)
From: Steven Rostedt <rostedt@goodmis.org>
When setting the funcgraph-args option when function graph tracer is net
enabled, it incorrectly enables it. Worse, it unregisters itself when it
was never registered. Then when it gets enabled again, it will register
itself a second time causing a WARNing.
~# echo 1 > /sys/kernel/tracing/options/funcgraph-args
~# head -20 /sys/kernel/tracing/trace
# tracer: nop
#
# entries-in-buffer/entries-written: 813/26317372 #P:8
#
# _-----=> irqs-off/BH-disabled
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / _-=> migrate-disable
# |||| / delay
# TASK-PID CPU# ||||| TIMESTAMP FUNCTION
# | | | ||||| | |
<idle>-0 [007] d..4. 358.966010: 7) 1.692 us | fetch_next_timer_interrupt(basej=4294981640, basem=357956000000, base_local=0xffff88823c3ae040, base_global=0xffff88823c3af300, tevt=0xffff888100e47cb8);
<idle>-0 [007] d..4. 358.966012: 7) | tmigr_cpu_deactivate(nextexp=357988000000) {
<idle>-0 [007] d..4. 358.966013: 7) | _raw_spin_lock(lock=0xffff88823c3b2320) {
<idle>-0 [007] d..4. 358.966014: 7) 0.981 us | preempt_count_add(val=1);
<idle>-0 [007] d..5. 358.966017: 7) 1.058 us | do_raw_spin_lock(lock=0xffff88823c3b2320);
<idle>-0 [007] d..4. 358.966019: 7) 5.824 us | }
<idle>-0 [007] d..5. 358.966021: 7) | tmigr_inactive_up(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
<idle>-0 [007] d..5. 358.966022: 7) | tmigr_update_events(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
Notice the "tracer: nop" at the top there. The current tracer is the "nop"
tracer, but the content is obviously the function graph tracer.
Enabling function graph tracing will cause it to register again and
trigger a warning in the accounting:
~# echo function_graph > /sys/kernel/tracing/current_tracer
-bash: echo: write error: Device or resource busy
With the dmesg of:
------------[ cut here ]------------
WARNING: CPU: 7 PID: 1095 at kernel/trace/ftrace.c:3509 ftrace_startup_subops+0xc1e/0x1000
Modules linked in: kvm_intel kvm irqbypass
CPU: 7 UID: 0 PID: 1095 Comm: bash Not tainted 6.16.0-rc2-test-00006-gea03de4105d3 #24 PREEMPT
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:ftrace_startup_subops+0xc1e/0x1000
Code: 48 b8 22 01 00 00 00 00 ad de 49 89 84 24 88 01 00 00 8b 44 24 08 89 04 24 e9 c3 f7 ff ff c7 04 24 ed ff ff ff e9 b7 f7 ff ff <0f> 0b c7 04 24 f0 ff ff ff e9 a9 f7 ff ff c7 04 24 f4 ff ff ff e9
RSP: 0018:ffff888133cff948 EFLAGS: 00010202
RAX: 0000000000000001 RBX: 1ffff1102679ff31 RCX: 0000000000000000
RDX: 1ffffffff0b27a60 RSI: ffffffff8593d2f0 RDI: ffffffff85941140
RBP: 00000000000c2041 R08: ffffffffffffffff R09: ffffed1020240221
R10: ffff88810120110f R11: ffffed1020240214 R12: ffffffff8593d2f0
R13: ffffffff8593d300 R14: ffffffff85941140 R15: ffffffff85631100
FS: 00007f7ec6f28740(0000) GS:ffff8882b5251000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ec6f181c0 CR3: 000000012f1d0005 CR4: 0000000000172ef0
Call Trace:
<TASK>
? __pfx_ftrace_startup_subops+0x10/0x10
? find_held_lock+0x2b/0x80
? ftrace_stub_direct_tramp+0x10/0x10
? ftrace_stub_direct_tramp+0x10/0x10
? trace_preempt_on+0xd0/0x110
? __pfx_trace_graph_entry_args+0x10/0x10
register_ftrace_graph+0x4d2/0x1020
? tracing_reset_online_cpus+0x14b/0x1e0
? __pfx_register_ftrace_graph+0x10/0x10
? ring_buffer_record_enable+0x16/0x20
? tracing_reset_online_cpus+0x153/0x1e0
? __pfx_tracing_reset_online_cpus+0x10/0x10
? __pfx_trace_graph_return+0x10/0x10
graph_trace_init+0xfd/0x160
tracing_set_tracer+0x500/0xa80
? __pfx_tracing_set_tracer+0x10/0x10
? lock_release+0x181/0x2d0
? _copy_from_user+0x26/0xa0
tracing_set_trace_write+0x132/0x1e0
? __pfx_tracing_set_trace_write+0x10/0x10
? ftrace_graph_func+0xcc/0x140
? ftrace_stub_direct_tramp+0x10/0x10
? ftrace_stub_direct_tramp+0x10/0x10
? ftrace_stub_direct_tramp+0x10/0x10
vfs_write+0x1d0/0xe90
? __pfx_vfs_write+0x10/0x10
Have the setting of the funcgraph-args check if function_graph tracer is
the current tracer of the instance, and if not, do nothing, as there's
nothing to do (the option is checked when function_graph tracing starts).
Cc: stable@vger.kernel.org
Fixes: c7a60a733c373 ("ftrace: Have funcgraph-args take affect during tracing")
Reported-by: duchangbin <changbin.du@huawei.com>
Closes: https://lore.kernel.org/all/4ab1a7bdd0174ab09c7b0d68cdbff9a4@huawei.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_functions_graph.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 9234e2c39abf..b6211c304c7f 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -455,10 +455,16 @@ static int graph_trace_init(struct trace_array *tr)
return 0;
}
+static struct tracer graph_trace;
+
static int ftrace_graph_trace_args(struct trace_array *tr, int set)
{
trace_func_graph_ent_t entry;
+ /* Do nothing if the current tracer is no this tracer */
+ if (tr->current_trace != &graph_trace)
+ return 0;
+
if (set)
entry = trace_graph_entry_args;
else
--
2.47.2On Tue, 17 Jun 2025 12:08:30 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
>
> When setting the funcgraph-args option when function graph tracer is net
> enabled, it incorrectly enables it. Worse, it unregisters itself when it
> was never registered. Then when it gets enabled again, it will register
> itself a second time causing a WARNing.
>
> ~# echo 1 > /sys/kernel/tracing/options/funcgraph-args
> ~# head -20 /sys/kernel/tracing/trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 813/26317372 #P:8
> #
> # _-----=> irqs-off/BH-disabled
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # | | | ||||| | |
> <idle>-0 [007] d..4. 358.966010: 7) 1.692 us | fetch_next_timer_interrupt(basej=4294981640, basem=357956000000, base_local=0xffff88823c3ae040, base_global=0xffff88823c3af300, tevt=0xffff888100e47cb8);
> <idle>-0 [007] d..4. 358.966012: 7) | tmigr_cpu_deactivate(nextexp=357988000000) {
> <idle>-0 [007] d..4. 358.966013: 7) | _raw_spin_lock(lock=0xffff88823c3b2320) {
> <idle>-0 [007] d..4. 358.966014: 7) 0.981 us | preempt_count_add(val=1);
> <idle>-0 [007] d..5. 358.966017: 7) 1.058 us | do_raw_spin_lock(lock=0xffff88823c3b2320);
> <idle>-0 [007] d..4. 358.966019: 7) 5.824 us | }
> <idle>-0 [007] d..5. 358.966021: 7) | tmigr_inactive_up(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
> <idle>-0 [007] d..5. 358.966022: 7) | tmigr_update_events(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
>
> Notice the "tracer: nop" at the top there. The current tracer is the "nop"
> tracer, but the content is obviously the function graph tracer.
>
> Enabling function graph tracing will cause it to register again and
> trigger a warning in the accounting:
>
> ~# echo function_graph > /sys/kernel/tracing/current_tracer
> -bash: echo: write error: Device or resource busy
>
> With the dmesg of:
>
> ------------[ cut here ]------------
> WARNING: CPU: 7 PID: 1095 at kernel/trace/ftrace.c:3509 ftrace_startup_subops+0xc1e/0x1000
> Modules linked in: kvm_intel kvm irqbypass
> CPU: 7 UID: 0 PID: 1095 Comm: bash Not tainted 6.16.0-rc2-test-00006-gea03de4105d3 #24 PREEMPT
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:ftrace_startup_subops+0xc1e/0x1000
> Code: 48 b8 22 01 00 00 00 00 ad de 49 89 84 24 88 01 00 00 8b 44 24 08 89 04 24 e9 c3 f7 ff ff c7 04 24 ed ff ff ff e9 b7 f7 ff ff <0f> 0b c7 04 24 f0 ff ff ff e9 a9 f7 ff ff c7 04 24 f4 ff ff ff e9
> RSP: 0018:ffff888133cff948 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 1ffff1102679ff31 RCX: 0000000000000000
> RDX: 1ffffffff0b27a60 RSI: ffffffff8593d2f0 RDI: ffffffff85941140
> RBP: 00000000000c2041 R08: ffffffffffffffff R09: ffffed1020240221
> R10: ffff88810120110f R11: ffffed1020240214 R12: ffffffff8593d2f0
> R13: ffffffff8593d300 R14: ffffffff85941140 R15: ffffffff85631100
> FS: 00007f7ec6f28740(0000) GS:ffff8882b5251000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7ec6f181c0 CR3: 000000012f1d0005 CR4: 0000000000172ef0
> Call Trace:
> <TASK>
> ? __pfx_ftrace_startup_subops+0x10/0x10
> ? find_held_lock+0x2b/0x80
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? trace_preempt_on+0xd0/0x110
> ? __pfx_trace_graph_entry_args+0x10/0x10
> register_ftrace_graph+0x4d2/0x1020
> ? tracing_reset_online_cpus+0x14b/0x1e0
> ? __pfx_register_ftrace_graph+0x10/0x10
> ? ring_buffer_record_enable+0x16/0x20
> ? tracing_reset_online_cpus+0x153/0x1e0
> ? __pfx_tracing_reset_online_cpus+0x10/0x10
> ? __pfx_trace_graph_return+0x10/0x10
> graph_trace_init+0xfd/0x160
> tracing_set_tracer+0x500/0xa80
> ? __pfx_tracing_set_tracer+0x10/0x10
> ? lock_release+0x181/0x2d0
> ? _copy_from_user+0x26/0xa0
> tracing_set_trace_write+0x132/0x1e0
> ? __pfx_tracing_set_trace_write+0x10/0x10
> ? ftrace_graph_func+0xcc/0x140
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> vfs_write+0x1d0/0xe90
> ? __pfx_vfs_write+0x10/0x10
>
> Have the setting of the funcgraph-args check if function_graph tracer is
> the current tracer of the instance, and if not, do nothing, as there's
> nothing to do (the option is checked when function_graph tracing starts).
>
OK, this looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thanks,
> Cc: stable@vger.kernel.org
> Fixes: c7a60a733c373 ("ftrace: Have funcgraph-args take affect during tracing")
> Reported-by: duchangbin <changbin.du@huawei.com>
> Closes: https://lore.kernel.org/all/4ab1a7bdd0174ab09c7b0d68cdbff9a4@huawei.com/
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> kernel/trace/trace_functions_graph.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 9234e2c39abf..b6211c304c7f 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -455,10 +455,16 @@ static int graph_trace_init(struct trace_array *tr)
> return 0;
> }
>
> +static struct tracer graph_trace;
> +
> static int ftrace_graph_trace_args(struct trace_array *tr, int set)
> {
> trace_func_graph_ent_t entry;
>
> + /* Do nothing if the current tracer is no this tracer */
> + if (tr->current_trace != &graph_trace)
> + return 0;
> +
> if (set)
> entry = trace_graph_entry_args;
> else
> --
> 2.47.2
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Hi, Steven,
On Tue, Jun 17, 2025 at 12:08:30PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
>
> When setting the funcgraph-args option when function graph tracer is net
> enabled, it incorrectly enables it. Worse, it unregisters itself when it
> was never registered. Then when it gets enabled again, it will register
> itself a second time causing a WARNing.
>
> ~# echo 1 > /sys/kernel/tracing/options/funcgraph-args
> ~# head -20 /sys/kernel/tracing/trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 813/26317372 #P:8
> #
> # _-----=> irqs-off/BH-disabled
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # | | | ||||| | |
> <idle>-0 [007] d..4. 358.966010: 7) 1.692 us | fetch_next_timer_interrupt(basej=4294981640, basem=357956000000, base_local=0xffff88823c3ae040, base_global=0xffff88823c3af300, tevt=0xffff888100e47cb8);
> <idle>-0 [007] d..4. 358.966012: 7) | tmigr_cpu_deactivate(nextexp=357988000000) {
> <idle>-0 [007] d..4. 358.966013: 7) | _raw_spin_lock(lock=0xffff88823c3b2320) {
> <idle>-0 [007] d..4. 358.966014: 7) 0.981 us | preempt_count_add(val=1);
> <idle>-0 [007] d..5. 358.966017: 7) 1.058 us | do_raw_spin_lock(lock=0xffff88823c3b2320);
> <idle>-0 [007] d..4. 358.966019: 7) 5.824 us | }
> <idle>-0 [007] d..5. 358.966021: 7) | tmigr_inactive_up(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
> <idle>-0 [007] d..5. 358.966022: 7) | tmigr_update_events(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
>
> Notice the "tracer: nop" at the top there. The current tracer is the "nop"
> tracer, but the content is obviously the function graph tracer.
>
> Enabling function graph tracing will cause it to register again and
> trigger a warning in the accounting:
>
> ~# echo function_graph > /sys/kernel/tracing/current_tracer
> -bash: echo: write error: Device or resource busy
>
> With the dmesg of:
>
> ------------[ cut here ]------------
> WARNING: CPU: 7 PID: 1095 at kernel/trace/ftrace.c:3509 ftrace_startup_subops+0xc1e/0x1000
> Modules linked in: kvm_intel kvm irqbypass
> CPU: 7 UID: 0 PID: 1095 Comm: bash Not tainted 6.16.0-rc2-test-00006-gea03de4105d3 #24 PREEMPT
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:ftrace_startup_subops+0xc1e/0x1000
> Code: 48 b8 22 01 00 00 00 00 ad de 49 89 84 24 88 01 00 00 8b 44 24 08 89 04 24 e9 c3 f7 ff ff c7 04 24 ed ff ff ff e9 b7 f7 ff ff <0f> 0b c7 04 24 f0 ff ff ff e9 a9 f7 ff ff c7 04 24 f4 ff ff ff e9
> RSP: 0018:ffff888133cff948 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 1ffff1102679ff31 RCX: 0000000000000000
> RDX: 1ffffffff0b27a60 RSI: ffffffff8593d2f0 RDI: ffffffff85941140
> RBP: 00000000000c2041 R08: ffffffffffffffff R09: ffffed1020240221
> R10: ffff88810120110f R11: ffffed1020240214 R12: ffffffff8593d2f0
> R13: ffffffff8593d300 R14: ffffffff85941140 R15: ffffffff85631100
> FS: 00007f7ec6f28740(0000) GS:ffff8882b5251000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7ec6f181c0 CR3: 000000012f1d0005 CR4: 0000000000172ef0
> Call Trace:
> <TASK>
> ? __pfx_ftrace_startup_subops+0x10/0x10
> ? find_held_lock+0x2b/0x80
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? trace_preempt_on+0xd0/0x110
> ? __pfx_trace_graph_entry_args+0x10/0x10
> register_ftrace_graph+0x4d2/0x1020
> ? tracing_reset_online_cpus+0x14b/0x1e0
> ? __pfx_register_ftrace_graph+0x10/0x10
> ? ring_buffer_record_enable+0x16/0x20
> ? tracing_reset_online_cpus+0x153/0x1e0
> ? __pfx_tracing_reset_online_cpus+0x10/0x10
> ? __pfx_trace_graph_return+0x10/0x10
> graph_trace_init+0xfd/0x160
> tracing_set_tracer+0x500/0xa80
> ? __pfx_tracing_set_tracer+0x10/0x10
> ? lock_release+0x181/0x2d0
> ? _copy_from_user+0x26/0xa0
> tracing_set_trace_write+0x132/0x1e0
> ? __pfx_tracing_set_trace_write+0x10/0x10
> ? ftrace_graph_func+0xcc/0x140
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> vfs_write+0x1d0/0xe90
> ? __pfx_vfs_write+0x10/0x10
>
> Have the setting of the funcgraph-args check if function_graph tracer is
> the current tracer of the instance, and if not, do nothing, as there's
> nothing to do (the option is checked when function_graph tracing starts).
>
> Cc: stable@vger.kernel.org
> Fixes: c7a60a733c373 ("ftrace: Have funcgraph-args take affect during tracing")
> Reported-by: duchangbin <changbin.du@huawei.com>
> Closes: https://lore.kernel.org/all/4ab1a7bdd0174ab09c7b0d68cdbff9a4@huawei.com/
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> kernel/trace/trace_functions_graph.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 9234e2c39abf..b6211c304c7f 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -455,10 +455,16 @@ static int graph_trace_init(struct trace_array *tr)
> return 0;
> }
>
> +static struct tracer graph_trace;
> +
> static int ftrace_graph_trace_args(struct trace_array *tr, int set)
> {
> trace_func_graph_ent_t entry;
>
> + /* Do nothing if the current tracer is no this tracer */
typo: no -> not
> + if (tr->current_trace != &graph_trace)
> + return 0;
> +
This can fix the issue. But how are tr->current_trace and &graph_trace linked?
When are they equal?
> if (set)
> entry = trace_graph_entry_args;
> else
> --
> 2.47.2
>
>
--
Cheers,
Changbin Du
On Wed, 18 Jun 2025 02:40:21 +0000
duchangbin <changbin.du@huawei.com> wrote:
> > diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> > index 9234e2c39abf..b6211c304c7f 100644
> > --- a/kernel/trace/trace_functions_graph.c
> > +++ b/kernel/trace/trace_functions_graph.c
> > @@ -455,10 +455,16 @@ static int graph_trace_init(struct trace_array *tr)
> > return 0;
> > }
> >
> > +static struct tracer graph_trace;
> > +
> > static int ftrace_graph_trace_args(struct trace_array *tr, int set)
> > {
> > trace_func_graph_ent_t entry;
> >
> > + /* Do nothing if the current tracer is no this tracer */
> typo: no -> not
Oops, thanks.
>
> > + if (tr->current_trace != &graph_trace)
> > + return 0;
> > +
> This can fix the issue. But how are tr->current_trace and &graph_trace linked?
> When are they equal?
register_tracer() passes in what tr->current_trace gets set to when the
tracer is active.
-- Steve
>
> > if (set)
> > entry = trace_graph_entry_args;
> > else
> > --
> > 2.47.2
Thanks! I've applied this patch, and it has fixed the issue.
Tested-by: Changbin Du <changbin.du@huawei.com>
On Tue, Jun 17, 2025 at 12:08:30PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
>
> When setting the funcgraph-args option when function graph tracer is net
> enabled, it incorrectly enables it. Worse, it unregisters itself when it
> was never registered. Then when it gets enabled again, it will register
> itself a second time causing a WARNing.
>
> ~# echo 1 > /sys/kernel/tracing/options/funcgraph-args
> ~# head -20 /sys/kernel/tracing/trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 813/26317372 #P:8
> #
> # _-----=> irqs-off/BH-disabled
> # / _----=> need-resched
> # | / _---=> hardirq/softirq
> # || / _--=> preempt-depth
> # ||| / _-=> migrate-disable
> # |||| / delay
> # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> # | | | ||||| | |
> <idle>-0 [007] d..4. 358.966010: 7) 1.692 us | fetch_next_timer_interrupt(basej=4294981640, basem=357956000000, base_local=0xffff88823c3ae040, base_global=0xffff88823c3af300, tevt=0xffff888100e47cb8);
> <idle>-0 [007] d..4. 358.966012: 7) | tmigr_cpu_deactivate(nextexp=357988000000) {
> <idle>-0 [007] d..4. 358.966013: 7) | _raw_spin_lock(lock=0xffff88823c3b2320) {
> <idle>-0 [007] d..4. 358.966014: 7) 0.981 us | preempt_count_add(val=1);
> <idle>-0 [007] d..5. 358.966017: 7) 1.058 us | do_raw_spin_lock(lock=0xffff88823c3b2320);
> <idle>-0 [007] d..4. 358.966019: 7) 5.824 us | }
> <idle>-0 [007] d..5. 358.966021: 7) | tmigr_inactive_up(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
> <idle>-0 [007] d..5. 358.966022: 7) | tmigr_update_events(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {
>
> Notice the "tracer: nop" at the top there. The current tracer is the "nop"
> tracer, but the content is obviously the function graph tracer.
>
> Enabling function graph tracing will cause it to register again and
> trigger a warning in the accounting:
>
> ~# echo function_graph > /sys/kernel/tracing/current_tracer
> -bash: echo: write error: Device or resource busy
>
> With the dmesg of:
>
> ------------[ cut here ]------------
> WARNING: CPU: 7 PID: 1095 at kernel/trace/ftrace.c:3509 ftrace_startup_subops+0xc1e/0x1000
> Modules linked in: kvm_intel kvm irqbypass
> CPU: 7 UID: 0 PID: 1095 Comm: bash Not tainted 6.16.0-rc2-test-00006-gea03de4105d3 #24 PREEMPT
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:ftrace_startup_subops+0xc1e/0x1000
> Code: 48 b8 22 01 00 00 00 00 ad de 49 89 84 24 88 01 00 00 8b 44 24 08 89 04 24 e9 c3 f7 ff ff c7 04 24 ed ff ff ff e9 b7 f7 ff ff <0f> 0b c7 04 24 f0 ff ff ff e9 a9 f7 ff ff c7 04 24 f4 ff ff ff e9
> RSP: 0018:ffff888133cff948 EFLAGS: 00010202
> RAX: 0000000000000001 RBX: 1ffff1102679ff31 RCX: 0000000000000000
> RDX: 1ffffffff0b27a60 RSI: ffffffff8593d2f0 RDI: ffffffff85941140
> RBP: 00000000000c2041 R08: ffffffffffffffff R09: ffffed1020240221
> R10: ffff88810120110f R11: ffffed1020240214 R12: ffffffff8593d2f0
> R13: ffffffff8593d300 R14: ffffffff85941140 R15: ffffffff85631100
> FS: 00007f7ec6f28740(0000) GS:ffff8882b5251000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7ec6f181c0 CR3: 000000012f1d0005 CR4: 0000000000172ef0
> Call Trace:
> <TASK>
> ? __pfx_ftrace_startup_subops+0x10/0x10
> ? find_held_lock+0x2b/0x80
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? trace_preempt_on+0xd0/0x110
> ? __pfx_trace_graph_entry_args+0x10/0x10
> register_ftrace_graph+0x4d2/0x1020
> ? tracing_reset_online_cpus+0x14b/0x1e0
> ? __pfx_register_ftrace_graph+0x10/0x10
> ? ring_buffer_record_enable+0x16/0x20
> ? tracing_reset_online_cpus+0x153/0x1e0
> ? __pfx_tracing_reset_online_cpus+0x10/0x10
> ? __pfx_trace_graph_return+0x10/0x10
> graph_trace_init+0xfd/0x160
> tracing_set_tracer+0x500/0xa80
> ? __pfx_tracing_set_tracer+0x10/0x10
> ? lock_release+0x181/0x2d0
> ? _copy_from_user+0x26/0xa0
> tracing_set_trace_write+0x132/0x1e0
> ? __pfx_tracing_set_trace_write+0x10/0x10
> ? ftrace_graph_func+0xcc/0x140
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> ? ftrace_stub_direct_tramp+0x10/0x10
> vfs_write+0x1d0/0xe90
> ? __pfx_vfs_write+0x10/0x10
>
> Have the setting of the funcgraph-args check if function_graph tracer is
> the current tracer of the instance, and if not, do nothing, as there's
> nothing to do (the option is checked when function_graph tracing starts).
>
> Cc: stable@vger.kernel.org
> Fixes: c7a60a733c373 ("ftrace: Have funcgraph-args take affect during tracing")
> Reported-by: duchangbin <changbin.du@huawei.com>
> Closes: https://lore.kernel.org/all/4ab1a7bdd0174ab09c7b0d68cdbff9a4@huawei.com/
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> kernel/trace/trace_functions_graph.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 9234e2c39abf..b6211c304c7f 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -455,10 +455,16 @@ static int graph_trace_init(struct trace_array *tr)
> return 0;
> }
>
> +static struct tracer graph_trace;
> +
> static int ftrace_graph_trace_args(struct trace_array *tr, int set)
> {
> trace_func_graph_ent_t entry;
>
> + /* Do nothing if the current tracer is no this tracer */
> + if (tr->current_trace != &graph_trace)
> + return 0;
> +
> if (set)
> entry = trace_graph_entry_args;
> else
> --
> 2.47.2
>
>
--
Cheers,
Changbin Du
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