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SubjectRe: [PATCH] tracing: Add trace_trigger kernel command line option
On Wed, 19 Oct 2022 20:01:37 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> @@ -90,6 +90,10 @@ int unregister_tracepoint_module_notifier(struct notifier_block *nb)
> #ifdef CONFIG_TRACEPOINTS
> static inline void tracepoint_synchronize_unregister(void)
> {
> + /* Early updates do not need synchronization */
> + if (early_boot_irqs_disabled)
> + return;
> +
> synchronize_srcu(&tracepoint_srcu);
> synchronize_rcu();

I wonder if this check should be just moved to the RCU synchronization
code? That is, if early_boot_irqs_disabled is set, do nothing, as there
should be nothing to synchronize against.

It took me a bit to figure out why I was constantly getting:

[ 1.072013] rcu: srcu_init: Setting srcu_struct sizes based on contention.
[ 1.078888] ------------[ cut here ]------------
[ 1.083422] Interrupts were enabled early
[ 1.087399] WARNING: CPU: 0 PID: 0 at init/main.c:1061 start_kernel+0x36f/0x4e8
[ 1.094656] Modules linked in:
[ 1.097683] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.1.0-rc1-test+ #461
[ 1.104509] Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
[ 1.113411] RIP: 0010:start_kernel+0x36f/0x4e8
[ 1.117817] Code: 48 27 5f e8 fd 7b 03 00 e8 55 72 e5 fe e8 6b 05 03 00 ff 15 2a f9 89 ff 0f ba e0 09 73 0e 48 c7 c7 98 26 31 a0 e8 01 5b df fe <0f> 0b c6 05 c7 2c af ff 00 e8 da 36 47 fe ff 15 14 f9 89 ff e8 56
[ 1.136485] RSP: 0000:ffffffffa0603f30 EFLAGS: 00010286
[ 1.141670] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[ 1.148754] RDX: 0000000000000002 RSI: 00000000ffffdfff RDI: 0000000000000001
[ 1.155840] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffffa0603dd8
[ 1.162926] R10: 0000000000000003 R11: ffffffffa0734168 R12: 000000000000180a
[ 1.170011] R13: 00000000010fecf0 R14: 0000000000000000 R15: 00000000d44e3018
[ 1.177097] FS: 0000000000000000(0000) GS:ffff91909aa00000(0000) knlGS:0000000000000000
[ 1.185131] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1.190835] CR2: ffff91909edff000 CR3: 000000007760a001 CR4: 00000000000606f0
[ 1.197924] Call Trace:
[ 1.200345] <TASK>


It was a bit of whack-a-mole in finding all the places that were calling
synchronize RCU.

-- Steve

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