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