linux-kernel - Re: [PATCH v2] trace: tracing_event_filter: fast path when no subsystem filters

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Date:   Tue, 3 Oct 2023 22:30:03 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nicholas Lowell <nicholas.lowell@...il.com>
Cc:     mhiramat@...nel.org, linux-kernel@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Nicholas Lowell <nlowell@...mark.com>
Subject: Re: [PATCH v2] trace: tracing_event_filter: fast path when no
 subsystem filters

On Mon,  2 Oct 2023 10:41:48 -0400
Nicholas Lowell <nicholas.lowell@...il.com> wrote:

> @@ -2411,7 +2418,12 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir,
>  	}
>  
>  	if (!strcmp(strstrip(filter_string), "0")) {
> -		filter_free_subsystem_preds(dir, tr);
> +		/* If nothing was freed, we do not need to sync */
> +		if (!filter_free_subsystem_preds(dir, tr)) {
> +			if(!(WARN_ON_ONCE(system->filter)))
> +				goto out_unlock;
> +		}
> +
>  		remove_filter_string(system->filter);
>  		filter = system->filter;
>  		system->filter = NULL;
> -- 

This is why I asked for the warning:

trace-cmd record -o /tmp/trace.dat -e sched -f "(common_pid == $$) || ((common_pid > 10) && common_pid < 100) || (common_pid >= 1000 && common_pid <= 1050) || (common_pid > 10000 && common_pid < 20000)" sleep 5


Causes:

------------[ cut here ]------------
 WARNING: CPU: 5 PID: 944 at kernel/trace/trace_events_filter.c:2423 apply_subsystem_event_filter+0x18c/0x5e0
 Modules linked in:
 CPU: 5 PID: 944 Comm: trace-cmd Not tainted 6.6.0-rc4-test-00009-gff7cd7446fe5 #102
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
 RIP: 0010:apply_subsystem_event_filter+0x18c/0x5e0
 Code: 44 24 08 00 00 00 00 48 8b 6d 00 4c 39 f5 75 bc 48 8b 44 24 18 4c 8b 60 18 4c 89 e5 45 84 ff 75 14 48 85 ed 0f 84 37 ff ff ff <0f> 0b eb 10 e8 4b be fd ff eb b0 4d 85 e4 0f 84 a3 02 00 00 48 8b
 RSP: 0018:ffff9b4941607db8 EFLAGS: 00010286
 RAX: ffff8b2780a77280 RBX: ffff8b2780a77400 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff8b2781c11c38 RDI: ffff8b2781c11c38
 RBP: ffff8b28df449030 R08: ffff8b2781c11c38 R09: 0000000000000000
 R10: ffff8b2781c11c38 R11: 0000000000000000 R12: ffff8b28df449030
 R13: ffffffffaaf64de0 R14: ffffffffaaf66bb8 R15: 0000000000000000
 FS:  00007fd221def3c0(0000) GS:ffff8b28f7d40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000056117c93e160 CR3: 000000010173a003 CR4: 0000000000170ee0
 Call Trace:
  <TASK>
  ? apply_subsystem_event_filter+0x18c/0x5e0
  ? __warn+0x81/0x130
  ? apply_subsystem_event_filter+0x18c/0x5e0
  ? report_bug+0x191/0x1c0
  ? handle_bug+0x3c/0x80
  ? exc_invalid_op+0x17/0x70
  ? asm_exc_invalid_op+0x1a/0x20
  ? apply_subsystem_event_filter+0x18c/0x5e0
  ? apply_subsystem_event_filter+0x5b/0x5e0
  ? __check_object_size+0x25b/0x2c0
  subsystem_filter_write+0x41/0x70
  vfs_write+0xf2/0x440
  ? kmem_cache_free+0x22/0x350
  ksys_write+0x6f/0xf0
  do_syscall_64+0x3f/0xc0
  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
 RIP: 0033:0x7fd221ee7ae0

-- Steve