linux-kernel - Re: [PATCH v2] tracing: Silence warning when chunk allocation fails in trace_pid

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Message-ID: <20250908150257.23731d24@gandalf.local.home>
Date: Mon, 8 Sep 2025 15:02:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Pu Lehui <pulehui@...weicloud.com>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tracing: Silence warning when chunk allocation fails
 in trace_pid_write

On Mon,  8 Sep 2025 02:46:58 +0000
Pu Lehui <pulehui@...weicloud.com> wrote:

> From: Pu Lehui <pulehui@...wei.com>
> 
> Syzkaller trigger a fault injection warning:
> 
> WARNING: CPU: 1 PID: 12326 at tracepoint_add_func+0xbfc/0xeb0
> Modules linked in:
> CPU: 1 UID: 0 PID: 12326 Comm: syz.6.10325 Tainted: G U 6.14.0-rc5-syzkaller #0
> Tainted: [U]=USER
> Hardware name: Google Compute Engine/Google Compute Engine
> RIP: 0010:tracepoint_add_func+0xbfc/0xeb0 kernel/tracepoint.c:294
> Code: 09 fe ff 90 0f 0b 90 0f b6 74 24 43 31 ff 41 bc ea ff ff ff
> RSP: 0018:ffffc9000414fb48 EFLAGS: 00010283
> RAX: 00000000000012a1 RBX: ffffffff8e240ae0 RCX: ffffc90014b78000
> RDX: 0000000000080000 RSI: ffffffff81bbd78b RDI: 0000000000000001
> RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000001 R12: ffffffffffffffef
> R13: 0000000000000000 R14: dffffc0000000000 R15: ffffffff81c264f0
> FS:  00007f27217f66c0(0000) GS:ffff8880b8700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b2e80dff8 CR3: 00000000268f8000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  tracepoint_probe_register_prio+0xc0/0x110 kernel/tracepoint.c:464
>  register_trace_prio_sched_switch include/trace/events/sched.h:222 [inline]
>  register_pid_events kernel/trace/trace_events.c:2354 [inline]
>  event_pid_write.isra.0+0x439/0x7a0 kernel/trace/trace_events.c:2425
>  vfs_write+0x24c/0x1150 fs/read_write.c:677
>  ksys_write+0x12b/0x250 fs/read_write.c:731
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> We can reproduce the warning by following the steps below:
> 1. echo 8 >> set_event_notrace_pid. Let tr->filtered_pids owns one pid
>    and register sched_switch tracepoint.
> 2. echo ' ' >> set_event_pid, and perform fault injection during chunk
>    allocation of trace_pid_list_alloc. Let pid_list with no pid and
> assign to tr->filtered_pids.
> 3. echo ' ' >> set_event_pid. Let pid_list is NULL and assign to
>    tr->filtered_pids.
> 4. echo 9 >> set_event_pid, will trigger the double register
>    sched_switch tracepoint warning.
> 
> The reason is that syzkaller injects a fault into the chunk allocation
> in trace_pid_list_alloc, causing a failure in trace_pid_list_set, which
> may trigger double register of the same tracepoint. This only occurs
> when the system is about to crash, but to suppress this warning, let's
> add failure handling logic to trace_pid_list_set.
> 
> Fixes: 8d6e90983ade ("tracing: Create a sparse bitmask for pid filtering")
> Reported-by: syzbot+161412ccaeff20ce4dde@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67cb890e.050a0220.d8275.022e.GAE@google.com
> Signed-off-by: Pu Lehui <pulehui@...wei.com>
> ---

FYI, when sending a v2, please state below the three dashes what was
changed since v1. Something like:

Changes since v1: https://lore.kernel.org/all/20250821071721.3609109-1-pulehui@huaweicloud.com/

- Instead of returning -EINVAL before trace_parser_load() have
  trace_pid_write() return error when trace_pid_list_set() returns an error.


I have a Link tag to this email that is added by my scripts, with the idea
that this email will have a link to the previous version and so on. It will
create a chain of the email discussions that lead to what lands in mainline.

-- Steve


>  kernel/trace/trace.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 1b7db732c0b1..f2a84d1ce4b7 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -834,7 +834,10 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
>  		/* copy the current bits to the new max */
>  		ret = trace_pid_list_first(filtered_pids, &pid);
>  		while (!ret) {
> -			trace_pid_list_set(pid_list, pid);
> +			ret = trace_pid_list_set(pid_list, pid);
> +			if (ret < 0)
> +				goto out;
> +
>  			ret = trace_pid_list_next(filtered_pids, pid + 1, &pid);
>  			nr_pids++;
>  		}
> @@ -871,6 +874,7 @@ int trace_pid_write(struct trace_pid_list *filtered_pids,
>  		trace_parser_clear(&parser);
>  		ret = 0;
>  	}
> + out:
>  	trace_parser_put(&parser);
>  
>  	if (ret < 0) {