On Wed, 4 Oct 2023 10:39:33 -0400
Nick Lowell <nicholas.low...@gmail.com> wrote:
> > ------------[ 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
>
> Is this just informative indicating that there are issues with how
> filters are being used or are you saying there is something else I
> need to do before this patch is approved?
> What version of trace-cmd is that using?
Not sure if it matters, but the above was with trace-cmd v3.2.
So, I guess we need to look a bit deeper at the change.
> @@ -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;
When do we want to skip the below?
The original version just did the "goto out_unlock" before the
"system->filter" check, and that would have caused a memory leak, or just
left the "system->filter" around when unneeded.
In other words, the patch is incorrect in general then.
> + }
> +
> remove_filter_string(system->filter);
> filter = system->filter;
> system->filter = NULL;
I believe, what you really want here is simply:
bool sync;
[..]
if (!strcmp(strstrip(filter_string), "0")) {
+ sync = filter_free_subsystem_preds(dir, tr);
remove_filter_string(system->filter);
filter = system->filter;
system->filter = NULL;
- /* Ensure all filters are no longer used */
- tracepoint_synchronize_unregister();
+ if (sync) {
+ /* Ensure all filters are no longer used */
+ tracepoint_synchronize_unregister();
+ }
filter_free_subsystem_filters(dir, tr);
Maybe even pass in "sync" to the filter_free_subsystem_filters() to make
sure there were nothing to be freed, and do the WARN_ON_ONCE() then.
__free_filter(filter);
goto out_unlock;
}
-- Steve
