| From 327e28664307d49ce3fa71ba30dcc0007c270974 Mon Sep 17 00:00:00 2001 |
| From: Steven Rostedt <rostedt@goodmis.org> |
| Date: Wed, 18 Jun 2025 07:38:01 -0400 |
| Subject: fgraph: Do not enable function_graph tracer when setting funcgraph-args |
| |
| From: Steven Rostedt <rostedt@goodmis.org> |
| |
| commit 327e28664307d49ce3fa71ba30dcc0007c270974 upstream. |
| |
| 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 |
| Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| Cc: Mark Rutland <mark.rutland@arm.com> |
| Link: https://lore.kernel.org/20250618073801.057ea636@gandalf.local.home |
| Fixes: c7a60a733c373 ("ftrace: Have funcgraph-args take affect during tracing") |
| Closes: https://lore.kernel.org/all/4ab1a7bdd0174ab09c7b0d68cdbff9a4@huawei.com/ |
| Reported-by: Changbin Du <changbin.du@huawei.com> |
| Tested-by: Changbin Du <changbin.du@huawei.com> |
| Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> |
| Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/trace/trace_functions_graph.c | 6 ++++++ |
| 1 file changed, 6 insertions(+) |
| |
| --- a/kernel/trace/trace_functions_graph.c |
| +++ b/kernel/trace/trace_functions_graph.c |
| @@ -475,10 +475,16 @@ static int graph_trace_init(struct trace |
| 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 not this tracer */ |
| + if (tr->current_trace != &graph_trace) |
| + return 0; |
| + |
| if (set) |
| entry = trace_graph_entry_args; |
| else |
