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

[Stephen Hemminger <stephen@networkplumber.org>]

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.

Even rte_dump_stack() is unsafe from these signals.

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

Should be constant.

> +
> +struct oops_signal {
> +	int sig;

Redundant, you defined the oops_signals above.

> +	bool enabled;

Redundant, you can just compare with action.

> +	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

> +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

> +{
> +	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?

> +
> +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.

> +	}
> +}
> +
> +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?

>  {
> -	RTE_SET_USED(signals);
> +	int count = 0, sig[RTE_OOPS_SIGNALS_MAX];
> +	unsigned int idx = 0;
>  
> -	return 0;
> +	for (idx = 0; idx < RTE_DIM(oops_signals); idx++) {
> +		if (signals_db[idx].enabled) {
> +			sig[count] = signals_db[idx].sig;
> +			count++;
> +		}
> +	}
> +	if (signals)
> +		memcpy(signals, sig, sizeof(*signals) * count);
> +
> +	return count;
>  }
>  
>  int
>  eal_oops_init(void)
>  {
> -	return 0;
> +	unsigned int idx, rc = 0;
> +	struct sigaction sa;
> +
> +	RTE_BUILD_BUG_ON(RTE_DIM(oops_signals) > RTE_OOPS_SIGNALS_MAX);
> +
> +	sigemptyset(&sa.sa_mask);
> +	sa.sa_sigaction = &eal_oops_handler;
> +	sa.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
> +
> +	for (idx = 0; idx < RTE_DIM(oops_signals); idx++) {
> +		signals_db[idx].sig = oops_signals[idx];
> +		/* Get exiting sigaction */
> +		rc = sigaction(signals_db[idx].sig, NULL, &signals_db[idx].sa);
> +		if (rc)
> +			continue;
> +		/* Replace with oops handler */
> +		rc = sigaction(signals_db[idx].sig, &sa, NULL);
> +		if (rc)
> +			continue;
> +		signals_db[idx].enabled = true;
> +	}
> +	return rc;
>  }
>  
>  void
>  eal_oops_fini(void)
>  {
> +	unsigned int idx;
> +
> +	for (idx = 0; idx < RTE_DIM(oops_signals); idx++) {
> +		if (!signals_db[idx].enabled)
> +			continue;
> +		/* Replace with stored handler */
> +		sigaction(signals_db[idx].sig, &signals_db[idx].sa, NULL);
> +	}
>  }