Re: [dpdk-dev] [PATCH v2 2/6] eal: oops handling API implementation

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Aug 17, 2021 at 9:22 AM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> On Tue, 17 Aug 2021 08:57:19 +0530
> <jerinj@marvell.com> wrote:
>
> > +#define oops_print(...) rte_log(RTE_LOG_ERR, RTE_LOGTYPE_EAL, __VA_ARGS__)
>
> It is problematic to call rte_log from a signal handler.
> The malloc pool maybe corrupted and rte_log can call functions that
> use malloc.

OK. What to use instead, fprint(stderr, ...)?

>
> Even rte_dump_stack() is unsafe from these signals.

OK

>
> > +
> > +static int oops_signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT, SIGFPE, SIGSYS};
>
> Should be constant.

Ack

>
> > +
> > +struct oops_signal {
> > +     int sig;
>
> Redundant, you defined the oops_signals above.

Ack.

>
> > +     bool enabled;
>
> Redundant, you can just compare with action.

Anyway, we need to database to hold the sigactions. This makes clean
to implement rte_oops_signals_enabled().
Also != SIG_DFL is not enabled.

>
> > +     struct sigaction sa;
> > +};
> > +
> > +static struct oops_signal signals_db[RTE_DIM(oops_signals)];
> > +
> > +static void
> > +back_trace_dump(ucontext_t *context)
> > +{
> > +     RTE_SET_USED(context);
> > +
> > +     rte_dump_stack();
> > +}
>
> rte_dump_stack() is not safe in signal handler:
>
> Recommend backtrace_symbols_fd ??
>
> Better yet use libunwind

libunwind is an optional dependency. You can see in the next patch,
back_trace_dump() will be implemented with libunwind based stack unwind,
if the dependency is met.


>
> > +static void
> > +siginfo_dump(int sig, siginfo_t *info)
> > +{
> > +     oops_print("PID:           %" PRIdMAX "\n", (intmax_t)getpid());
> > +
> > +     if (info == NULL)
> > +             return;
> > +     if (sig != info->si_signo)
> > +             oops_print("Invalid signal info\n");
> > +
> > +     oops_print("Signal number: %d\n", info->si_signo);
> > +     oops_print("Fault address: %p\n", info->si_addr);
> > +}
> > +
> > +static void
> > +mem32_dump(void *ptr)
>
> Should be const

Ack.

>
> > +{
> > +     uint32_t *p = ptr;
> > +     int i;
> > +
> > +     for (i = 0; i < 16; i++)
> > +             oops_print("%p: 0x%x\n", p + i, rte_be_to_cpu_32(p[i]));
> > +}
 >
> Why reinvent hexdump?

Make sense. I can change to hexdump, But, it will use rte_log. Shouldn't we use
fprint(stderr,..) variant.

>
> > +
> > +static void
> > +stack_dump_header(void)
> > +{
> > +     oops_print("Stack dump:\n");
> > +     oops_print("----------\n");
> > +}
> > +
> > +static void
> > +code_dump_header(void)
> > +{
> > +     oops_print("Code dump:\n");
> > +     oops_print("----------\n");
> > +}
> > +
> > +static void
> > +stack_code_dump(void *stack, void *code)
> > +{
> > +     if (stack == NULL || code == NULL)
> > +             return;
> > +
> > +     oops_print("\n");
> > +     stack_dump_header();
> > +     mem32_dump(stack);
> > +     oops_print("\n");
> > +
> > +     code_dump_header();
> > +     mem32_dump(code);
> > +     oops_print("\n");
> > +}
> > +static void
> > +archinfo_dump(ucontext_t *uc)
> >  {
> > -     RTE_SET_USED(sig);
> > -     RTE_SET_USED(info);
> >       RTE_SET_USED(uc);
> >
> > +     stack_code_dump(NULL, NULL);
> > +}
> > +
> > +static void
> > +default_signal_handler_invoke(int sig)
> > +{
> > +     unsigned int idx;
> > +
> > +     for (idx = 0; idx < RTE_DIM(oops_signals); idx++) {
> > +             /* Skip disabled signals */
> > +             if (signals_db[idx].sig != sig)
> > +                     continue;
> > +             if (!signals_db[idx].enabled)
> > +                     continue;
> > +             /* Replace with stored handler */
> > +             sigaction(sig, &signals_db[idx].sa, NULL);
> > +             kill(getpid(), sig);
>
> If you use SA_RESETHAND, you don't need this stuff.

As mentioned in other 1/6 email reply, This is NOT the case where
SIG_DFL handler
called from eal oops handler, instead, it will be calling the signal
handler which
is registered prior to rte_eal_init() which is stored local database.



>
> > +     }
> > +}
> > +
> > +void
> > +rte_oops_decode(int sig, siginfo_t *info, ucontext_t *uc)
> > +{
> > +     oops_print("Signal info:\n");
> > +     oops_print("------------\n");
> > +     siginfo_dump(sig, info);
> > +     oops_print("\n");
> > +
> > +     oops_print("Backtrace:\n");
> > +     oops_print("----------\n");
> > +     back_trace_dump(uc);
> > +     oops_print("\n");
> > +
> > +     oops_print("Arch info:\n");
> > +     oops_print("----------\n");
> > +     if (uc)
> > +             archinfo_dump(uc);
> > +}
> > +
> > +static void
> > +eal_oops_handler(int sig, siginfo_t *info, void *ctx)
> > +{
> > +     ucontext_t *uc = ctx;
> > +
> > +     rte_oops_decode(sig, info, uc);
> > +     default_signal_handler_invoke(sig);
>
> If you use SA_RESETHAND, then just doing raise(sig) here.
> >  }
> >
> >  int
> >  rte_oops_signals_enabled(int *signals)
>
> Why is this necessary and exported?

Explained in 1/6 email reply.