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105 lines
4.7 KiB
105 lines
4.7 KiB
commit c2f5813ae0a68f6c6d69e66dac2da6e46b9df034 |
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Author: Joseph Myers <joseph@codesourcery.com> |
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Date: Wed Mar 18 17:05:38 2015 +0000 |
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Make sem_timedwait use FUTEX_CLOCK_REALTIME (bug 18138). |
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sem_timedwait converts absolute timeouts to relative to pass them to |
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the futex syscall. (Before the recent reimplementation, on x86_64 it |
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used FUTEX_CLOCK_REALTIME, but not on other architectures.) |
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Correctly implementing POSIX requirements, however, requires use of |
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FUTEX_CLOCK_REALTIME; passing a relative timeout to the kernel does |
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not conform to POSIX. The POSIX specification for sem_timedwait says |
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"The timeout shall be based on the CLOCK_REALTIME clock.". The POSIX |
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specification for clock_settime says "If the value of the |
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CLOCK_REALTIME clock is set via clock_settime(), the new value of the |
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clock shall be used to determine the time of expiration for absolute |
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time services based upon the CLOCK_REALTIME clock. This applies to the |
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time at which armed absolute timers expire. If the absolute time |
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requested at the invocation of such a time service is before the new |
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value of the clock, the time service shall expire immediately as if |
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the clock had reached the requested time normally.". If a relative |
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timeout is passed to the kernel, it is interpreted according to the |
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CLOCK_MONOTONIC clock, and so fails to meet that POSIX requirement in |
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the event of clock changes. |
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This patch makes sem_timedwait use lll_futex_timed_wait_bitset with |
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FUTEX_CLOCK_REALTIME when possible, as done in some other places in |
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NPTL. FUTEX_CLOCK_REALTIME is always available for supported Linux |
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kernel versions; unavailability of lll_futex_timed_wait_bitset is only |
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an issue for hppa (an issue noted in |
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<https://sourceware.org/glibc/wiki/PortStatus>, and fixed by the |
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unreviewed |
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<https://sourceware.org/ml/libc-alpha/2014-12/msg00655.html> that |
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removes the hppa lowlevellock.h completely). |
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In the FUTEX_CLOCK_REALTIME case, the glibc code still needs to check |
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for negative tv_sec and handle that as timeout, because the Linux |
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kernel returns EINVAL not ETIMEDOUT for that case, so resulting in |
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failures of nptl/tst-abstime and nptl/tst-sem13 in the absence of that |
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check. If we're trying to distinguish between Linux-specific and |
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generic-futex NPTL code, I suppose having this in an nptl/ file isn't |
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ideal, but there doesn't seem to be any better place at present. |
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It's not possible to add a testcase for this issue to the testsuite |
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because of the requirement to change the system clock as part of a |
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test (this is a case where testing would require some form of |
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container, with root in that container, and one whose CLOCK_REALTIME |
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is isolated from that of the host; I'm not sure what forms of |
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containers, short of a full virtual machine, provide that clock |
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isolation). |
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Tested for x86_64. Also tested for powerpc with the testcase included |
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in the bug. |
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[BZ #18138] |
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* nptl/sem_waitcommon.c: Include <kernel-features.h>. |
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(futex_abstimed_wait) |
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[__ASSUME_FUTEX_CLOCK_REALTIME && lll_futex_timed_wait_bitset]: |
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Use lll_futex_timed_wait_bitset with FUTEX_CLOCK_REALTIME instead |
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of lll_futex_timed_wait. |
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Index: glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c |
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=================================================================== |
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--- glibc-2.17-c758a686.orig/nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c |
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+++ glibc-2.17-c758a686/nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c |
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@@ -17,6 +17,7 @@ |
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License along with the GNU C Library; if not, see |
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<http://www.gnu.org/licenses/>. */ |
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+#include <kernel-features.h> |
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#include <errno.h> |
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#include <sysdep.h> |
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#include <lowlevellock.h> |
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@@ -45,6 +46,13 @@ futex_abstimed_wait (unsigned int* futex |
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} |
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else |
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{ |
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+#if (defined __ASSUME_FUTEX_CLOCK_REALTIME \ |
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+ && defined lll_futex_timed_wait_bitset) |
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+ /* The Linux kernel returns EINVAL for this, but in userspace |
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+ such a value is valid. */ |
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+ if (abstime->tv_sec < 0) |
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+ return ETIMEDOUT; |
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+#else |
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struct timeval tv; |
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struct timespec rt; |
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int sec, nsec; |
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@@ -68,9 +76,16 @@ futex_abstimed_wait (unsigned int* futex |
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/* Do wait. */ |
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rt.tv_sec = sec; |
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rt.tv_nsec = nsec; |
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+#endif |
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if (cancel) |
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oldtype = __pthread_enable_asynccancel (); |
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+#if (defined __ASSUME_FUTEX_CLOCK_REALTIME \ |
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+ && defined lll_futex_timed_wait_bitset) |
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+ err = lll_futex_timed_wait_bitset (futex, expected, abstime, |
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+ FUTEX_CLOCK_REALTIME, private); |
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+#else |
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err = lll_futex_timed_wait (futex, expected, &rt, private); |
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+#endif |
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if (cancel) |
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__pthread_disable_asynccancel (oldtype); |
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}
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