A Kernel Bug Froze My Machine: Debugging an Async-Profiler Deadlock

Re:A Kernel Bug Froze My Machine: Debugging an Async-Profile... by jerrinot on Monday December 15, 2025 @04:24PM (#46280890)

Author here. I've always been kernel-curious despite never having worked on one myself. Consider this either a collection of impractical party tricks or a hands-on way to get a feel for kernel internals.

[ Parent | on HN ]

Re:A Kernel Bug Froze My Machine: Debugging an Async-Profile... by ChuckMcM on Monday December 15, 2025 @04:50PM (#46281224)

Question, isn't this a bug? static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer) { - if (event->state != PERF_EVENT_STATE_ACTIVE) + if (event->state != PERF_EVENT_STATE_ACTIVE || + event->hw.state & PERF_HES_STOPPED) return HRTIMER_NORESTART;

The bug being that the precedence of || is higher than the precedence of != ? Consider writing it if ((event->state != PERF_EVENT_STATE_ACTIVE) || (event->hw_state & PERF_HES_STOPPED))

This coming from a person who has too many scars from not parenthesizing my expressions in conditionals to ensure they work the way I meant them to work.

[ Parent | on HN ]

Re:A Kernel Bug Froze My Machine: Debugging an Async-Profile... by jerrinot on Monday December 15, 2025 @05:00PM (#46281346)

Wow, someone is actually reading the article in detail, that's a good feeling! In C, the != operator has higher precedence than the || operator. That said, extra parentheses never hurt readability.

[ Parent | on HN ]

Re:A Kernel Bug Froze My Machine: Debugging an Async-Profile... by unsnap_biceps on Monday December 15, 2025 @05:32PM (#46281751)

Which language(s?) have || before !=/==?

[ Parent | on HN ]

Re:A Kernel Bug Froze My Machine: Debugging an Async-Profile... by anematode on Monday December 15, 2025 @06:37PM (#46282574)

Likely they're confusing it with bitwise OR, since in C, a | b == c parses as a | (b == c), causing widespread pain.

[ Parent | on HN ]