* Andrii Nakryiko <[email protected]> wrote:
> It is useful to be able to access current->mm at task exit to, say, > record a bunch of VMA information right before the task exits (e.g., for > stack symbolization reasons when dealing with short-lived processes that > exit in the middle of profiling session). Currently, > trace_sched_process_exit() is triggered after exit_mm() which resets > current->mm to NULL making this tracepoint unsuitable for inspecting > and recording task's mm_struct-related data when tracing process > lifetimes. > > There is a particularly suitable place, though, right after > taskstats_exit() is called, but before we do exit_mm() and other > exit_*() resource teardowns. taskstats performs a similar kind of > accounting that some applications do with BPF, and so co-locating them > seems like a good fit. So that's where trace_sched_process_exit() is > moved with this patch. > > Also, existing trace_sched_process_exit() tracepoint is notoriously > missing `group_dead` flag that is certainly useful in practice and some > of our production applications have to work around this. So plumb > `group_dead` through while at it, to have a richer and more complete > tracepoint. > > Note that we can't use sched_process_template anymore, and so we use > TRACE_EVENT()-based tracepoint definition. But all the field names and > order, as well as assign and output logic remain intact. We just add one > extra field at the end in backwards-compatible way. > > Signed-off-by: Andrii Nakryiko <[email protected]> > --- > include/trace/events/sched.h | 28 +++++++++++++++++++++++++--- > kernel/exit.c | 2 +- > 2 files changed, 26 insertions(+), 4 deletions(-) > > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h > index 8994e97d86c1..05a14f2b35c3 100644 > --- a/include/trace/events/sched.h > +++ b/include/trace/events/sched.h > @@ -328,9 +328,31 @@ DEFINE_EVENT(sched_process_template, sched_process_free, > /* > * Tracepoint for a task exiting: > */ > -DEFINE_EVENT(sched_process_template, sched_process_exit, > - TP_PROTO(struct task_struct *p), > - TP_ARGS(p)); > +TRACE_EVENT(sched_process_exit, > + > + TP_PROTO(struct task_struct *p, bool group_dead), > + > + TP_ARGS(p, group_dead), > + > + TP_STRUCT__entry( > + __array( char, comm, TASK_COMM_LEN ) > + __field( pid_t, pid ) > + __field( int, prio ) > + __field( bool, group_dead ) > + ), > + > + TP_fast_assign( > + memcpy(__entry->comm, p->comm, TASK_COMM_LEN); > + __entry->pid = p->pid; > + __entry->prio = p->prio; /* XXX SCHED_DEADLINE */ > + __entry->group_dead = group_dead; > + ), > + > + TP_printk("comm=%s pid=%d prio=%d group_dead=%s", > + __entry->comm, __entry->pid, __entry->prio, > + __entry->group_dead ? "true" : "false" > + ) This feels really fragile, could you please at least add a comment that points out that this is basically an extension of sched_process_template, and that it should remain a subset of it, or something to that end? Thanks, Ingo
