Re: selftests: user_events: ftrace_test - RIP: 0010:tracing_update_buffers (kernel/trace/trace.c:6470)

Beau Belgrave
2023-10-30T16:31:14Z

On Fri, Oct 27, 2023 at 10:33:44PM -0400, Steven Rostedt wrote:
> On Fri, 27 Oct 2023 18:36:40 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > On Fri, 27 Oct 2023 12:20:11 -0700
> > Beau Belgrave <beaub@linux.microsoft.com> wrote:
> >
> > > On Fri, Oct 27, 2023 at 05:38:41PM +0530, Naresh Kamboju wrote:
> > > > Following kernel crash noticed on x86_64 while running selftests: user_events:
> > > > ftrace_test running 6.6.0-rc7-next-20231026.
> > > >
> > > > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > > >
> > > > kselftest: Running tests in user_events
> > > > TAP version 13
> > > > 1..4
> > > > # timeout set to 90
> > > > # selftests: user_events: ftrace_test
> > > > [ 2391.606817] general protection fault, probably for non-canonical
> > > > address 0x6b6b6b6b6b6b8a83: 0000 [#1] PREEMPT SMP PTI
> > > > [ 2391.617519] CPU: 1 PID: 34662 Comm: ftrace_test Not tainted
> > > > 6.6.0-rc7-next-20231026 #1
> > > > [ 2391.625428] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> > > > 2.7 12/07/2021
> > > > [ 2391.632811] RIP: 0010:tracing_update_buffers (kernel/trace/trace.c:6470)
> > > > [ 2391.637952] Code: 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00
> > > > 55 31 f6 48 89 e5 41 55 41 54 53 48 89 fb 48 c7 c7 40 8c 61 94 e8 92
> > > > d3 5a 01 <44> 0f b6 a3 18 1f 00 00 41 80 fc 01 0f 87 c8 dc 4e 01 45 31
> >
> >
> >
> > > Warning is from this code:
> > > static void __trace_array_put(struct trace_array *this_tr)
> > > {
> > > WARN_ON(!this_tr->ref);
> > > this_tr->ref--;
> > > }
> > >
> > > It seems like there might be a timing window or an incorrect call to
> > > trace_array_put() somewhere. Do you think this is related to the eventfs
> > > work?
> >
> > No, I think this is was probably introduced by:
> >
> > a1f157c7a3bb ("tracing: Expand all ring buffers individually")
> >
> > Or possibly a mixture of the two changes? But anyway I think I need to look
> > at this one first.
>

I applied both [1][2] patches, and I no longer get any panics. However,
I still get the splat about the trace_array_put when running
user_event's ftrace selftest:

[ 26.665931] ------------[ cut here ]------------
[ 26.666663] WARNING: CPU: 12 PID: 291 at kernel/trace/trace.c:516 tracing_release_file_tr+0x46/0x50
[ 26.667470] Modules linked in:
[ 26.667808] CPU: 12 PID: 291 Comm: ftrace_test Not tainted 6.6.0-rc7-next-20231026 #3
[ 26.668665] RIP: 0010:tracing_release_file_tr+0x46/0x50
[ 26.669093] Code: d1 03 01 8b 83 c0 1e 00 00 85 c0 74 1d 83 e8 01 48 c7 c7 80 5b ef bc 89 83 c0 1e 00 00 e8 f2 b5 03 01 31 c0 5b e9 75 ee 27 01 <0f> 0b eb df 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90
[ 26.670580] RSP: 0018:ffffb6ef858ffee8 EFLAGS: 00010246
[ 26.671128] RAX: 0000000000000000 RBX: ffff9d7ae2364058 RCX: 0000000000000000
[ 26.671793] RDX: 0000000000000000 RSI: ffffffffbcb6b38b RDI: 00000000ffffffff
[ 26.672444] RBP: ffff9d7ac3e72200 R08: 0000000000000000 R09: 0000000000000000
[ 26.673072] R10: ffffb6ef858ffee8 R11: ffffffffbb28526f R12: 00000000000f801f
[ 26.673705] R13: ffff9d7b661a2020 R14: ffff9d7ac6057728 R15: 0000000000000000
[ 26.674339] FS: 00007fa852fa6740(0000) GS:ffff9d81a6300000(0000) knlGS:0000000000000000
[ 26.674978] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 26.675506] CR2: 00007fa852c2a250 CR3: 0000000105d92001 CR4: 0000000000370eb0
[ 26.676142] Call Trace:
[ 26.676357] <TASK>
[ 26.676572] ? __warn+0x7f/0x160
[ 26.677092] ? tracing_release_file_tr+0x46/0x50
[ 26.677540] ? report_bug+0x1c3/0x1d0
[ 26.677871] ? handle_bug+0x3c/0x70
[ 26.678196] ? exc_invalid_op+0x14/0x70
[ 26.678520] ? asm_exc_invalid_op+0x16/0x20
[ 26.678845] ? tracing_release_file_tr+0x1f/0x50
[ 26.679268] ? tracing_release_file_tr+0x46/0x50
[ 26.679691] ? tracing_release_file_tr+0x1f/0x50
[ 26.680105] __fput+0xab/0x300
[ 26.680437] __x64_sys_close+0x38/0x80
[ 26.680757] do_syscall_64+0x41/0xf0
[ 26.681329] entry_SYSCALL_64_after_hwframe+0x6c/0x74
[ 26.681784] RIP: 0033:0x7fa852d15157
[ 26.682126] Code: ff e8 0d 16 02 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 7c 24 0c e8 83 b8 f7 ff
[ 26.684255] RSP: 002b:00007ffd226914f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[ 26.684939] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa852d15157
[ 26.685602] RDX: 0000000000000002 RSI: 0000560ad54567d4 RDI: 0000000000000005
[ 26.686257] RBP: 00007ffd22691520 R08: 0000000000000000 R09: 00007fa852fa6740
[ 26.686877] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd22691758
[ 26.687480] R13: 0000560ad5455ae7 R14: 0000560ad5458c38 R15: 00007fa8530d4040
[ 26.688107] </TASK>
[ 26.688315] irq event stamp: 1361
[ 26.688618] hardirqs last enabled at (1369): [<ffffffffbb1d7f49>] console_unlock+0x109/0x130
[ 26.689339] hardirqs last disabled at (1376): [<ffffffffbb1d7f2e>] console_unlock+0xee/0x130
[ 26.690062] softirqs last enabled at (1272): [<ffffffffbb14ba2a>] irq_exit_rcu+0x8a/0xe0
[ 26.690774] softirqs last disabled at (1267): [<ffffffffbb14ba2a>] irq_exit_rcu+0x8a/0xe0
[ 26.691620] ---[ end trace 0000000000000000 ]---

Thanks,
-Beau

1. https://lore.kernel.org/linux-trace-kernel/20231030115018.25399dbd@gandalf.local.home/
2. https://lore.kernel.org/linux-trace-kernel/20231028164650.4f5ea18a@rorschach.local.home/

> Not sure if the bug Beau hit is the same as this one, but the one Beau
> hit I think is fixed by this:
>
> -- Steve
>
> diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
> index 4d2da7480e5f..4a54493b8419 100644
> --- a/fs/tracefs/event_inode.c
> +++ b/fs/tracefs/event_inode.c
> @@ -234,6 +234,10 @@ create_file_dentry(struct eventfs_inode *ei, struct dentry **e_dentry,
> bool invalidate = false;
>
> mutex_lock(&eventfs_mutex);
> + if (ei->is_freed) {
> + mutex_unlock(&eventfs_mutex);
> + return NULL;
> + }
> /* If the e_dentry already has a dentry, use it */
> if (*e_dentry) {
> /* lookup does not need to up the ref count */