systemtap/rhbz2149666.patch

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commit 7eed8d1fef36997b9e4c1d9cdb67643483a51e56
Author: William Cohen <wcohen@redhat.com>
Date: Fri Nov 4 11:12:05 2022 -0400
Ensure that SystemTap runtime uses smp_processor_id() in proper context
There were cases on Fedora 36 and Rawhide running kernels with
CONFIG_DEBUG_PREEMPT=y where systemtap scripts would trigger kernel
log messages like the following:
[ 257.544406] check_preemption_disabled: 4 callbacks suppressed
[ 257.544409] BUG: using smp_processor_id() in preemptible [00000000] code: staprun/2106
[ 257.544465] caller is _stp_runtime_context_trylock+0x12/0x70 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544507] CPU: 0 PID: 2106 Comm: staprun Tainted: G OE ------- --- 6.1.0-0.rc2.20221028git23758867219c.24.fc38.x86_64 #1
[ 257.544544] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-1.fc36 04/01/2014
[ 257.544571] Call Trace:
[ 257.544583] <TASK>
[ 257.544593] dump_stack_lvl+0x5b/0x77
[ 257.544620] check_preemption_disabled+0xe1/0xf0
[ 257.544641] _stp_runtime_context_trylock+0x12/0x70 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544673] _stp_runtime_entryfn_get_context+0xb/0x70 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544705] _stp_ctl_send+0x76/0x1e0 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544735] _stp_transport_init+0x71a/0x860 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544771] ? kallsyms_on_each_symbol+0x30/0x30 [stap_e36600406768aeefd49daf9fc7a3d23c_2106]
[ 257.544803] do_one_initcall+0x6b/0x320
[ 257.544827] do_init_module+0x4a/0x200
[ 257.544844] __do_sys_init_module+0x16a/0x1a0
[ 257.544870] do_syscall_64+0x58/0x80
[ 257.544885] ? up_read+0x17/0x20
[ 257.544902] ? lock_is_held_type+0xe8/0x140
[ 257.544921] ? asm_exc_page_fault+0x22/0x30
[ 257.544939] ? lockdep_hardirqs_on+0x7d/0x100
[ 257.544956] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 257.544975] RIP: 0033:0x7f3cde12f5de
[ 257.544992] Code: 48 8b 0d 35 68 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 af 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 02 68 0c 00 f7 d8 64 89 01 48
[ 257.545010] RSP: 002b:00007ffc5170c418 EFLAGS: 00000246 ORIG_RAX: 00000000000000af
[ 257.545010] RAX: ffffffffffffffda RBX: 0000563620bd4020 RCX: 00007f3cde12f5de
[ 257.545010] RDX: 0000563620bd4020 RSI: 0000000000040ea0 RDI: 00007f3cde44a010
[ 257.545010] RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
[ 257.545010] R10: 0000000000000053 R11: 0000000000000246 R12: 00007ffc5170c510
[ 257.545010] R13: 00007f3cde44a010 R14: 00007ffc5170c440 R15: 00007f3cde4631e8
[ 257.545010] </TASK>
This issue was introduced by git commit 1641b6e7ea which added a fast
path check that used smp_processor_id() without first having a
preempt_disable(). The code now ensures that preemption is disabled
before using the smp_processor_id().
diff --git a/runtime/linux/runtime_context.h b/runtime/linux/runtime_context.h
index 3ed3cbd22..ee3870f32 100644
--- a/runtime/linux/runtime_context.h
+++ b/runtime/linux/runtime_context.h
@@ -49,13 +49,18 @@ static bool _stp_runtime_context_trylock(void)
{
bool locked;
+ /* Need to disable preemption because of the smp_processor_id() call
+ in _stp_runtime_get_context(). */
+ preempt_disable();
+
/* fast path to ignore new online CPUs without percpu context memory
* allocations. this also serves as an extra safe guard for NULL context
* pointers. */
- if (unlikely(_stp_runtime_get_context() == NULL))
+ if (unlikely(_stp_runtime_get_context() == NULL)) {
+ preempt_enable_no_resched();
return false;
+ }
- preempt_disable();
locked = atomic_add_unless(&_stp_contexts_busy_ctr, 1, INT_MAX);
if (!locked)
preempt_enable_no_resched();