On 03/16, Mathieu Desnoyers wrote: > > utrace_add_engine() > set_notify_resume(target); > > ok, so this is where the TIF_NOTIFY_RESUME thread flag is set. I notice > that it is set asynchronously with the execution of the target thread > (as I do with my TIF_KERNEL_TRACE thread flag). > > However, on x86_64, _TIF_DO_NOTIFY_MASK is only tested in > entry_64.S > > int_signal: > and > retint_signal: > > code paths. However, if there is no syscall tracing to do upon syscall > entry, the thread flags are not re-read at syscall exit and you will > miss the syscall exit returning from your target thread if this thread > was blocked while you set its TIF_NOTIFY_RESUME.
Afaics, TIF_NOTIFY_RESUME is not needed to trace syscall entry/exit. If engine wants the syscall tracing, utrace_set_events(UTRACE_SYSCALL_xxx) sets TIF_SYSCALL_TRACE. And syscall_trace_enter/syscall_trace_leave call tracehook_report_syscall_xxx(). Oleg.
