2017-09-21 20:10:52

by Shuah Khan

Subject: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

do_timer_oneshot() uses select() as a timer with FD_SETSIZE and readfs
is cleared with FD_ZERO without FD_SET.

When stdout and stderr are redirected, the test hangs in select forever.
Fix the problem calling select() with readfds empty and nfds zero. This
is sufficient for using select() for timer.

With this fix "./set-timer-lat > /dev/null 2>&1" no longer hangs.

Signed-off-by: Shuah Khan <[email protected]>
---
tools/testing/selftests/timers/set-timer-lat.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
index ab2fe225e051..3c248f0dc0d5 100644
--- a/tools/testing/selftests/timers/set-timer-lat.c
+++ b/tools/testing/selftests/timers/set-timer-lat.c
@@ -229,7 +229,6 @@ int do_timer_oneshot(int clock_id, int flags)
timer_t tm1;
const int interval = 0;
struct timeval timeout;
- fd_set fds;
int err;

err = setup_timer(clock_id, flags, interval, &tm1);
@@ -238,9 +237,8 @@ int do_timer_oneshot(int clock_id, int flags)

memset(&timeout, 0, sizeof(timeout));
timeout.tv_sec = 5;
- FD_ZERO(&fds);
do {
- err = select(FD_SETSIZE, &fds, NULL, NULL, &timeout);
+ err = select(0, NULL, NULL, NULL, &timeout);
} while (err == -1 && errno == EINTR);

timer_delete(tm1);
--
2.11.0

2017-09-22 14:42:17

by Shuah Khan

Subject: Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

Hi John/Greg,

On 09/21/2017 02:10 PM, Shuah Khan wrote:
> do_timer_oneshot() uses select() as a timer with FD_SETSIZE and readfs
> is cleared with FD_ZERO without FD_SET.
>
> When stdout and stderr are redirected, the test hangs in select forever.
> Fix the problem calling select() with readfds empty and nfds zero. This
> is sufficient for using select() for timer.
>
> With this fix "./set-timer-lat > /dev/null 2>&1" no longer hangs.
>
> Signed-off-by: Shuah Khan <[email protected]>
> ---
> tools/testing/selftests/timers/set-timer-lat.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
> index ab2fe225e051..3c248f0dc0d5 100644
> --- a/tools/testing/selftests/timers/set-timer-lat.c
> +++ b/tools/testing/selftests/timers/set-timer-lat.c
> @@ -229,7 +229,6 @@ int do_timer_oneshot(int clock_id, int flags)
> timer_t tm1;
> const int interval = 0;
> struct timeval timeout;
> - fd_set fds;
> int err;
>
> err = setup_timer(clock_id, flags, interval, &tm1);
> @@ -238,9 +237,8 @@ int do_timer_oneshot(int clock_id, int flags)
>
> memset(&timeout, 0, sizeof(timeout));
> timeout.tv_sec = 5;
> - FD_ZERO(&fds);
> do {
> - err = select(FD_SETSIZE, &fds, NULL, NULL, &timeout);
> + err = select(0, NULL, NULL, NULL, &timeout);
> } while (err == -1 && errno == EINTR);
>
> timer_delete(tm1);
>

I assume you are good with this fix. I plan to apply it to linux-kselftest fixes
today. Please let me know if you have any objections.

thanks,
-- Shuah

2017-09-22 15:41:56

by Greg Hackmann

Subject: Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

On 09/22/2017 07:42 AM, Shuah Khan wrote:
> Hi John/Greg,
>
> On 09/21/2017 02:10 PM, Shuah Khan wrote:
>> do_timer_oneshot() uses select() as a timer with FD_SETSIZE and readfs
>> is cleared with FD_ZERO without FD_SET.
>>
>> When stdout and stderr are redirected, the test hangs in select forever.
>> Fix the problem calling select() with readfds empty and nfds zero. This
>> is sufficient for using select() for timer.
>>
>> With this fix "./set-timer-lat > /dev/null 2>&1" no longer hangs.
>>
>> Signed-off-by: Shuah Khan <[email protected]>
>> ---
>> tools/testing/selftests/timers/set-timer-lat.c | 4 +---
>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
>> index ab2fe225e051..3c248f0dc0d5 100644
>> --- a/tools/testing/selftests/timers/set-timer-lat.c
>> +++ b/tools/testing/selftests/timers/set-timer-lat.c
>> @@ -229,7 +229,6 @@ int do_timer_oneshot(int clock_id, int flags)
>> timer_t tm1;
>> const int interval = 0;
>> struct timeval timeout;
>> - fd_set fds;
>> int err;
>>
>> err = setup_timer(clock_id, flags, interval, &tm1);
>> @@ -238,9 +237,8 @@ int do_timer_oneshot(int clock_id, int flags)
>>
>> memset(&timeout, 0, sizeof(timeout));
>> timeout.tv_sec = 5;
>> - FD_ZERO(&fds);
>> do {
>> - err = select(FD_SETSIZE, &fds, NULL, NULL, &timeout);
>> + err = select(0, NULL, NULL, NULL, &timeout);
>> } while (err == -1 && errno == EINTR);
>>
>> timer_delete(tm1);
>>
>
> I assume you are good with this fix. I plan to apply it to linux-kselftest fixes
> today. Please let me know if you have any objections.
>
> thanks,
> -- Shuah
>

Thanks for looking into this.

Acked-by: Greg Hackmann <[email protected]>

2017-09-22 17:31:10

by John Stultz

Subject: Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

On Fri, Sep 22, 2017 at 7:42 AM, Shuah Khan <[email protected]> wrote:
> Hi John/Greg,
>
> On 09/21/2017 02:10 PM, Shuah Khan wrote:
>> do_timer_oneshot() uses select() as a timer with FD_SETSIZE and readfs
>> is cleared with FD_ZERO without FD_SET.
>>
>> When stdout and stderr are redirected, the test hangs in select forever.
>> Fix the problem calling select() with readfds empty and nfds zero. This
>> is sufficient for using select() for timer.
>>
>> With this fix "./set-timer-lat > /dev/null 2>&1" no longer hangs.
>>
>> Signed-off-by: Shuah Khan <[email protected]>
>> ---
>> tools/testing/selftests/timers/set-timer-lat.c | 4 +---
>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
>> index ab2fe225e051..3c248f0dc0d5 100644
>> --- a/tools/testing/selftests/timers/set-timer-lat.c
>> +++ b/tools/testing/selftests/timers/set-timer-lat.c
>> @@ -229,7 +229,6 @@ int do_timer_oneshot(int clock_id, int flags)
>> timer_t tm1;
>> const int interval = 0;
>> struct timeval timeout;
>> - fd_set fds;
>> int err;
>>
>> err = setup_timer(clock_id, flags, interval, &tm1);
>> @@ -238,9 +237,8 @@ int do_timer_oneshot(int clock_id, int flags)
>>
>> memset(&timeout, 0, sizeof(timeout));
>> timeout.tv_sec = 5;
>> - FD_ZERO(&fds);
>> do {
>> - err = select(FD_SETSIZE, &fds, NULL, NULL, &timeout);
>> + err = select(0, NULL, NULL, NULL, &timeout);
>> } while (err == -1 && errno == EINTR);
>>
>> timer_delete(tm1);
>>
>
> I assume you are good with this fix. I plan to apply it to linux-kselftest fixes
> today. Please let me know if you have any objections.

No objections from me, just has been a busy few days and haven't had a
chance to test.

thanks
-john