Re: [dpdk-dev] [PATCH] Remove printf from signal handler.

["Li, Xiaoyun" <xiaoyun.li@intel.com>]

Hi
I don't have a good solution here.
Removing doesn't seem a good idea because there are many important alerts or reminders in all of those function calls and they may be called in other places too.
I think replacing with "write" can't solve the problem too. Because behavior like stopping port will call driver functions. It's not very reasonable to me that replacing all possible logs. 
Use a flag and check the flag for each possible thread? Most examples already do this way. But for complicated app, it will be tricky and may cause other issues.

Maybe other people have better ideas?

BRs
Xiaoyun

> -----Original Message-----
> From: prateekag <prateekag@cse.iitb.ac.in>
> Sent: Thursday, December 10, 2020 08:28
> To: Li, Xiaoyun <xiaoyun.li@intel.com>
> Cc: Prateek Agarwal <pratekag@gmail.com>; dev@dpdk.org;
> thomas@monjalon.net
> Subject: Re: [dpdk-dev] [PATCH] Remove printf from signal handler.
> 
> Hi
> Agree. What is the way out? The printfs you mentioned look like important
> messages and may have been called outside signal handler routines.
> Shall they be removed as well or converted to "write" function call? Or we live
> with the possiblity of deadlock howsoever unlikely.
> Regards
> Prateek Agarwal
> 
> 
> On 2020-12-08 08:28, Li, Xiaoyun wrote:
> > Hi
> > I don't object with all the removing of printf.
> > Just one concern, I don't think you actually solved the problem in
> > this patch.
> >
> > Take testpmd as an example, the signal_handler includes many
> > complicated actions after that very first printf like force_quit()
> > which includes stop port, close port, hotplug... and of course a lot of printf in it.
> > So only removing the first printf doesn't actually solve the issue you
> > mentioned.
> >
> > And many examples do similar things as testpmd, they have the same
> > issues too.
> >
> > BRs
> > Xiaoyun
> >
> >> -----Original Message-----
> >> From: dev <dev-bounces@dpdk.org> On Behalf Of Prateek Agarwal
> >> Sent: Saturday, December 5, 2020 01:52
> >> To: dev@dpdk.org
> >> Cc: thomas@monjalon.net; Prateek Agarwal <pratekag@gmail.com>;
> >> Prateek Agarwal <prateekag@cse.iitb.ac.in>
> >> Subject: [dpdk-dev] [PATCH] Remove printf from signal handler.
> >>
> >> printf is not async-signal safe. Using printf in signal handlers may
> >> lead to deadlock. Removed printf from signal handlers present in
> >> several applications.
> >>
> >> Signed-off-by: Prateek Agarwal <prateekag@cse.iitb.ac.in>
> >> ---
> >>  app/pdump/main.c             | 2 --
> >>  app/test-eventdev/evt_main.c | 4 ----
> >>  app/test-flow-perf/main.c    | 3 ---
> >>  app/test-pmd/testpmd.c       | 2 --
> >>  app/test/test_pmd_perf.c     | 1 -
> >>  5 files changed, 12 deletions(-)
> >>
> >> diff --git a/app/pdump/main.c b/app/pdump/main.c index
> >> b34bf3353..380f0ea0f 100644
> >> --- a/app/pdump/main.c
> >> +++ b/app/pdump/main.c
> >> @@ -573,8 +573,6 @@ static void
> >>  signal_handler(int sig_num)
> >>  {
> >>  	if (sig_num == SIGINT) {
> >> -		printf("\n\nSignal %d received, preparing to exit...\n",
> >> -				sig_num);
> >>  		quit_signal = 1;
> >>  	}
> >>  }
> >> diff --git a/app/test-eventdev/evt_main.c
> >> b/app/test-eventdev/evt_main.c index a8d304bab..51d5897f8 100644
> >> --- a/app/test-eventdev/evt_main.c
> >> +++ b/app/test-eventdev/evt_main.c
> >> @@ -22,12 +22,8 @@ signal_handler(int signum)  {
> >>  	int i;
> >>  	static uint8_t once;
> >> -
> >>  	if ((signum == SIGINT || signum == SIGTERM) && !once) {
> >>  		once = true;
> >> -		printf("\nSignal %d received, preparing to exit...\n",
> >> -				signum);
> >> -
> >>  		if (test != NULL) {
> >>  			/* request all lcores to exit from the main loop */
> >>  			*(int *)test->test_priv = true;
> >> diff --git a/app/test-flow-perf/main.c b/app/test-flow-perf/main.c
> >> index
> >> 03d01a8b5..aeb0ef3b0 100644
> >> --- a/app/test-flow-perf/main.c
> >> +++ b/app/test-flow-perf/main.c
> >> @@ -1001,9 +1001,6 @@ static void
> >>  signal_handler(int signum)
> >>  {
> >>  	if (signum == SIGINT || signum == SIGTERM) {
> >> -		printf("\n\nSignal %d received, preparing to exit...\n",
> >> -					signum);
> >> -		printf("Error: Stats are wrong due to sudden signal!\n\n");
> >>  		force_quit = true;
> >>  	}
> >>  }
> >> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c index
> >> 33fc0fddf..7ec87e7fd 100644
> >> --- a/app/test-pmd/testpmd.c
> >> +++ b/app/test-pmd/testpmd.c
> >> @@ -3794,8 +3794,6 @@ static void
> >>  signal_handler(int signum)
> >>  {
> >>  	if (signum == SIGINT || signum == SIGTERM) {
> >> -		printf("\nSignal %d received, preparing to exit...\n",
> >> -				signum);
> >>  #ifdef RTE_LIB_PDUMP
> >>  		/* uninitialize packet capture framework */
> >>  		rte_pdump_uninit();
> >> diff --git a/app/test/test_pmd_perf.c b/app/test/test_pmd_perf.c
> >> index
> >> 4db816a36..58cb84401 100644
> >> --- a/app/test/test_pmd_perf.c
> >> +++ b/app/test/test_pmd_perf.c
> >> @@ -319,7 +319,6 @@ signal_handler(int signum)  {
> >>  	/*  USR1 signal, stop testing */
> >>  	if (signum == SIGUSR1) {
> >> -		printf("Force Stop!\n");
> >>  		stop = 1;
> >>  	}
> >>
> >> --
> >> 2.25.1