----- On Mar 9, 2017, at 8:44 AM, Dorau, Lukasz lukasz.dorau@xxxxxxxxx wrote: > Hi, > > Could someone explain me why return probes of some syscalls (for example: futex, > poll, epoll_wait) sometimes are not called? > > It can be reproduced using the following bash script: > https://gist.github.com/ldorau/c439d9ec7635409a5016c42e3a9121ec > > Here are results gathered from 60 seconds test run on kernel 4.9.12 (Fedora 24): > > futex: p 56904 r 5489 (90% did not return (51415)) > poll: p 43466 r 7703 (82% did not return (35763)) > epoll_wait: p 73366 r 23551 (67% did not return (49815)) Most likely scenario: those processes are still blocked on those system calls when your tracing ends. AFAIU, another possible (less frequent) scenario: a process gets killed with SIGKILL while blocked on the signal. Thanks, Mathieu > > The whole log is attached below. > > Lukasz > > --- > # ./test_kprobes.sh 60 > > Will trace using following kprobe_events: > r:kprobes/r_futex sys_futex > p:kprobes/p_futex sys_futex > r:kprobes/r_poll sys_poll > p:kprobes/p_poll sys_poll > r:kprobes/r_epoll_wait sys_epoll_wait > p:kprobes/p_epoll_wait sys_epoll_wait > r:kprobes/r_select sys_select > p:kprobes/p_select sys_select > r:kprobes/r_fork sys_fork > p:kprobes/p_fork sys_fork > r:kprobes/r_vfork sys_vfork > p:kprobes/p_vfork sys_vfork > r:kprobes/r_mmap sys_mmap > p:kprobes/p_mmap sys_mmap > r:kprobes/r_open sys_open > p:kprobes/p_open sys_open > r:kprobes/r_close sys_close > p:kprobes/p_close sys_close > r:kprobes/r_write sys_write > p:kprobes/p_write sys_write > r:kprobes/r_read sys_read > p:kprobes/p_read sys_read > > Results (60 sec): > futex: p 56904 r 5489 (90% did not return (51415)) > poll: p 43466 r 7703 (82% did not return (35763)) > epoll_wait: p 73366 r 23551 (67% did not return (49815)) > select: p 13355 r 13351 (0% did not return (4)) > fork: p 0 r 0 (OK) > vfork: p 0 r 0 (OK) > mmap: p 4328 r 4328 (OK) > open: p 4579 r 4579 (OK) > close: p 7163 r 7163 (OK) > write: p 22769 r 22769 (OK) > read: p 40014 r 40014 (OK) > > -- > To unsubscribe from this list: send the line "unsubscribe linux-trace-users" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-trace-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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