diff mbox series

[v3,3/4] linux: Normalize and return timeout on select (BZ #27651)

Message ID 20210409155346.1357023-3-adhemerval.zanella@linaro.org
State Committed
Headers show
Series [v3,1/4] libsupport: Add support_select_modifies_timeout | expand

Commit Message

Adhemerval Zanella April 9, 2021, 3:53 p.m. UTC
The commit 2433d39b697, which added time64 support to select, changed
the function to use __NR_pselect6 (or __NR_pelect6_time64) on all
architectures.  However, on architectures where the symbol was
implemented with __NR_select the kernel normalizes the passed timeout
instead of return EINVAL.  For instance, the input timeval
{ 0, 5000000 } is interpreted as { 5, 0 }.

And as indicated by BZ #27651, this semantic seems to be expected
and changing it results in some performance issues (most likely
the program does not check the return code and keeps issuing
select with unormalized tv_usec argument).

To avoid a different semantic depending whether which syscall the
architecture used to issue, select now always normalize the timeout
input.  This is a slight change for some ABIs (for instance aarch64).

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 include/time.h                   |  5 ++++
 misc/tst-select.c                | 17 ++++++++++++
 sunrpc/svcauth_des.c             |  1 -
 sysdeps/unix/sysv/linux/select.c | 44 +++++++++++++++++++++++++-------
 4 files changed, 57 insertions(+), 10 deletions(-)

Comments

Andreas Schwab April 12, 2021, 8:28 a.m. UTC | #1
On Apr 09 2021, Adhemerval Zanella via Libc-alpha wrote:

> @@ -52,10 +74,13 @@ __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
>           (though the pselect() glibc call suppresses this behavior).
>           Since select() on Linux has the same behavior as the pselect6
>           syscall, we update the timeout here.  */
> -      if (r == 0 || errno != ENOSYS)
> +      if (r >= 0 || errno != ENOSYS)
>  	{
>  	  if (timeout != NULL)
> -	    TIMEVAL_TO_TIMESPEC (timeout, &ts64);
> +	    {
> +	      timeout->tv_sec = ts64.tv_sec;
> +	      timeout->tv_usec = ts64.tv_nsec / NSEC_PER_USEC;
> +	    }

What's wrong with TIMESPEC_TO_TIMEVAL?

Andreas.
Adhemerval Zanella April 12, 2021, 12:20 p.m. UTC | #2
On 12/04/2021 05:28, Andreas Schwab wrote:
> On Apr 09 2021, Adhemerval Zanella via Libc-alpha wrote:
> 
>> @@ -52,10 +74,13 @@ __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
>>           (though the pselect() glibc call suppresses this behavior).
>>           Since select() on Linux has the same behavior as the pselect6
>>           syscall, we update the timeout here.  */
>> -      if (r == 0 || errno != ENOSYS)
>> +      if (r >= 0 || errno != ENOSYS)
>>  	{
>>  	  if (timeout != NULL)
>> -	    TIMEVAL_TO_TIMESPEC (timeout, &ts64);
>> +	    {
>> +	      timeout->tv_sec = ts64.tv_sec;
>> +	      timeout->tv_usec = ts64.tv_nsec / NSEC_PER_USEC;
>> +	    }
> 
> What's wrong with TIMESPEC_TO_TIMEVAL?
> 
> Andreas.
> 

None in fact, I will adjust to use TIMESPEC_TO_TIMEVAL.
Adhemerval Zanella April 12, 2021, 6:26 p.m. UTC | #3
On 12/04/2021 09:20, Adhemerval Zanella wrote:
> 
> 
> On 12/04/2021 05:28, Andreas Schwab wrote:
>> On Apr 09 2021, Adhemerval Zanella via Libc-alpha wrote:
>>
>>> @@ -52,10 +74,13 @@ __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
>>>           (though the pselect() glibc call suppresses this behavior).
>>>           Since select() on Linux has the same behavior as the pselect6
>>>           syscall, we update the timeout here.  */
>>> -      if (r == 0 || errno != ENOSYS)
>>> +      if (r >= 0 || errno != ENOSYS)
>>>  	{
>>>  	  if (timeout != NULL)
>>> -	    TIMEVAL_TO_TIMESPEC (timeout, &ts64);
>>> +	    {
>>> +	      timeout->tv_sec = ts64.tv_sec;
>>> +	      timeout->tv_usec = ts64.tv_nsec / NSEC_PER_USEC;
>>> +	    }
>>
>> What's wrong with TIMESPEC_TO_TIMEVAL?
>>
>> Andreas.
>>
> 
> None in fact, I will adjust to use TIMESPEC_TO_TIMEVAL.
> 

Are you ok with the patch with the TIMESPEC_TO_TIMEVAL change?
Andreas Schwab April 12, 2021, 7:20 p.m. UTC | #4
On Apr 12 2021, Adhemerval Zanella wrote:

> Are you ok with the patch with the TIMESPEC_TO_TIMEVAL change?

Yes.

Andreas.
diff mbox series

Patch

diff --git a/include/time.h b/include/time.h
index caf2af5e74..e0636132a6 100644
--- a/include/time.h
+++ b/include/time.h
@@ -502,6 +502,11 @@  time_now (void)
   __clock_gettime (TIME_CLOCK_GETTIME_CLOCKID, &ts);
   return ts.tv_sec;
 }
+
+#define NSEC_PER_SEC    1000000000L  /* Nanoseconds per second.  */
+#define USEC_PER_SEC    1000000L     /* Microseconds per second.  */
+#define NSEC_PER_USEC   1000L        /* Nanoseconds per microsecond.  */
+
 #endif
 
 #endif
diff --git a/misc/tst-select.c b/misc/tst-select.c
index 5ad057cd51..534105b500 100644
--- a/misc/tst-select.c
+++ b/misc/tst-select.c
@@ -19,6 +19,7 @@ 
 #include <errno.h>
 #include <support/capture_subprocess.h>
 #include <support/check.h>
+#include <support/support.h>
 #include <support/timespec.h>
 #include <support/xunistd.h>
 #include <support/xtime.h>
@@ -47,6 +48,12 @@  do_test_child (void *clousure)
   int r = select (args->fds[0][0] + 1, &rfds, NULL, NULL, &args->tmo);
   TEST_COMPARE (r, 0);
 
+  if (support_select_modifies_timeout ())
+    {
+      TEST_COMPARE (args->tmo.tv_sec, 0);
+      TEST_COMPARE (args->tmo.tv_usec, 0);
+    }
+
   TEST_TIMESPEC_NOW_OR_AFTER (CLOCK_REALTIME, ts);
 
   xwrite (args->fds[1][1], "foo", 3);
@@ -69,6 +76,16 @@  do_test (void)
 				      sc_allow_none);
   }
 
+  if (support_select_normalizes_timeout ())
+    {
+      /* This is handled as 1 second instead of failing with EINVAL.  */
+      args.tmo = (struct timeval) { .tv_sec = 0, .tv_usec = 1000000 };
+      struct support_capture_subprocess result;
+      result = support_capture_subprocess (do_test_child, &args);
+      support_capture_subprocess_check (&result, "tst-select-child", 0,
+					sc_allow_none);
+    }
+
   /* Same as before, but simulating polling.  */
   args.tmo = (struct timeval) { .tv_sec = 0, .tv_usec = 0 };
   {
diff --git a/sunrpc/svcauth_des.c b/sunrpc/svcauth_des.c
index 7607abc818..25a85c9097 100644
--- a/sunrpc/svcauth_des.c
+++ b/sunrpc/svcauth_des.c
@@ -58,7 +58,6 @@ 
 
 #define debug(msg)		/*printf("svcauth_des: %s\n", msg) */
 
-#define USEC_PER_SEC ((uint32_t) 1000000L)
 #define BEFORE(t1, t2) timercmp(t1, t2, <)
 
 /*
diff --git a/sysdeps/unix/sysv/linux/select.c b/sysdeps/unix/sysv/linux/select.c
index 415aa87d3c..8deab751c0 100644
--- a/sysdeps/unix/sysv/linux/select.c
+++ b/sysdeps/unix/sysv/linux/select.c
@@ -33,12 +33,34 @@  int
 __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 	    struct __timeval64 *timeout)
 {
-  struct __timespec64 ts64, *pts64 = NULL;
-  if (timeout != NULL)
+  __time64_t s = timeout != NULL ? timeout->tv_sec : 0;
+  int32_t us = timeout != NULL ? timeout->tv_usec : 0;
+  int32_t ns;
+
+  if (s < 0 || us < 0)
+    return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
+
+  /* Normalize the timeout, as legacy Linux __NR_select and __NR__newselect.
+     Different than syscall, it also handle possible overflow.  */
+  if (us / USEC_PER_SEC > INT64_MAX - s)
     {
-      ts64 = timeval64_to_timespec64 (*timeout);
-      pts64 = &ts64;
+      s = INT64_MAX;
+      ns = NSEC_PER_SEC - 1;
     }
+  else
+    {
+      s += us / USEC_PER_SEC;
+      us = us % USEC_PER_SEC;
+      ns = us * NSEC_PER_USEC;
+    }
+
+  struct __timespec64 ts64, *pts64 = NULL;
+   if (timeout != NULL)
+     {
+       ts64.tv_sec = s;
+       ts64.tv_nsec = ns;
+       pts64 = &ts64;
+     }
 
 #ifndef __NR_pselect6_time64
 # define __NR_pselect6_time64 __NR_pselect6
@@ -52,10 +74,13 @@  __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
          (though the pselect() glibc call suppresses this behavior).
          Since select() on Linux has the same behavior as the pselect6
          syscall, we update the timeout here.  */
-      if (r == 0 || errno != ENOSYS)
+      if (r >= 0 || errno != ENOSYS)
 	{
 	  if (timeout != NULL)
-	    TIMEVAL_TO_TIMESPEC (timeout, &ts64);
+	    {
+	      timeout->tv_sec = ts64.tv_sec;
+	      timeout->tv_usec = ts64.tv_nsec / NSEC_PER_USEC;
+	    }
 	  return r;
 	}
 
@@ -64,14 +89,15 @@  __select64 (int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
 
 #ifndef __ASSUME_TIME64_SYSCALLS
   struct timespec ts32, *pts32 = NULL;
-  if (timeout != NULL)
+  if (pts64 != NULL)
     {
-      if (! in_time_t_range (timeout->tv_sec))
+      if (! in_time_t_range (pts64->tv_sec))
 	{
 	  __set_errno (EINVAL);
 	  return -1;
 	}
-      ts32 = valid_timespec64_to_timespec (ts64);
+      ts32.tv_sec = s;
+      ts32.tv_nsec = ns;
       pts32 = &ts32;
     }
 # ifndef __ASSUME_PSELECT