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linux: Normalize and return timeout on select (BZ #27651) 

The commit 2433d39b69, 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.
This commit is contained in:
Adhemerval Zanella 2021-03-31 13:53:34 -03:00
parent 49a40ba18e
commit 9d7c5cc38e
4 changed files with 54 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/time.h
View File

@ -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

17
misc/tst-select.c
View File

@ -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 };
{

1
sunrpc/svcauth_des.c
View File

@ -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, <)
/*

41
sysdeps/unix/sysv/linux/select.c
View File

@ -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 +74,10 @@ __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);
TIMESPEC_TO_TIMEVAL (timeout, &ts64);
return r;
}
@ -64,14 +86,15 @@ __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