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17 lines
838 B
Org Mode
17 lines
838 B
Org Mode
* Demonstration of close() hang on bpf_link fd close
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This is a minimal example to demonstrate an issue where =close()='ing an fd for a
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bpf_link kernel structure will hang indefinitely if the system is fully loaded.
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This only happens on a kernel compiled with =CONFIG_PREEMPT=y=, but on such a
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kernel the issue is quite easy to trigger: Simply load up the system (with work
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inside the kernel; sending it a lot of network traffic works pretty well), and
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run the bpf-link-hang program as root. The program will hang until load is
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lowered...
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The hang happens in =synchronize_rcu_tasks()=, which can be seen with this
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bpftrace invocation:
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#+begin_src sh
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bpftrace -e 'kprobe:synchronize_rcu_tasks { @start = nsecs; printf("enter\n"); } kretprobe:synchronize_rcu_tasks { printf("exit after %d ms\n", (nsecs - @start) / 1000000); }'
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#+end_src
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