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Remove CPU set size checking from affinity functions [BZ #19143]

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With current kernel versions, the check does not reliably detect that
unavailable CPUs are requested, for these reasons:

(1) The kernel will silently ignore non-allowed CPUs, that is, CPUs
    which are physically present but disallowed for the thread
    based on system configuration.

(2) Similarly, CPU bits which lack an online CPU (possible CPUs)
    are ignored.

(3) The existing probing code assumes that the CPU mask size is a
    power of two and at least 1024.  Neither has it to be a power
    of two, nor is the minimum possible value 1024, so the value
    determined is often too large.  This means that the CPU set
    size check in glibc accepts CPU bits beyond the actual hard
    system limit.

(4) Future kernel versions may not even have a fixed CPU set size.

After the removal of the probing code, the kernel still returns
EINVAL if no CPU in the requested set remains which can run the
thread after the affinity change.

Applications which care about the exact affinity mask will have
to query it using sched_getaffinity after setting it.  Due to the
effects described above, this commit does not change this.

The new tests supersede tst-getcpu, which is removed.  This
addresses bug 19164 because the new tests allocate CPU sets
dynamically.

	* nptl/check-cpuset.h: Remove.
	* nptl/pthread_attr_setaffinity.c (__pthread_attr_setaffinity_new):
	Remove CPU set size check.
	* nptl/pthread_setattr_default_np.c (pthread_setattr_default_np):
	Likewise.
	* sysdeps/unix/sysv/linux/check-cpuset.h: Remove.
	* sysdeps/unix/sysv/linux/pthread_setaffinity.c
	(__kernel_cpumask_size, __determine_cpumask_size): Remove.
	(__pthread_setaffinity_new): Remove CPU set size check.
	* sysdeps/unix/sysv/linux/sched_setaffinity.c
	(__kernel_cpumask_size): Remove.
	(__sched_setaffinity_new): Remove CPU set size check.
	* manual/threads.texi (Default Thread Attributes): Remove stale
	reference to check_cpuset_attr, determine_cpumask_size in comment.
	* sysdeps/unix/sysv/linux/Makefile [$(subdir) == posix] (tests):
	Remove tst-getcpu.  Add tst-affinity, tst-affinity-pid.
	[$(subdir) == nptl] (tests): Add tst-thread-affinity-pthread,
	tst-thread-affinity-pthread2, tst-thread-affinity-sched.
	* sysdeps/unix/sysv/linux/tst-affinity.c: New file.
	* sysdeps/unix/sysv/linux/tst-affinity-pid.c: New file.
	* sysdeps/unix/sysv/linux/tst-skeleton-affinity.c: New skeleton test file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-sched.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-pthread.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-affinity-pthread2.c: New file.
	* sysdeps/unix/sysv/linux/tst-thread-skeleton-affinity.c: New
	skeleton test file.
	* sysdeps/unix/sysv/linux/tst-getcpu.c: Remove.  Superseded by
	tst-affinity-pid.
This commit is contained in:
Florian Weimer
2015-11-24 17:21:01 +01:00
parent c100dca32a
commit 2359035ac5
17 changed files with 1007 additions and 219 deletions
Download Patch File Download Diff File Expand all files Collapse all files

48
sysdeps/unix/sysv/linux/pthread_setaffinity.c
View File

@ -23,62 +23,14 @@
#include <shlib-compat.h>
size_t __kernel_cpumask_size attribute_hidden;
/* Determine the size of cpumask_t in the kernel. */
int
__determine_cpumask_size (pid_t tid)
{
size_t psize;
int res;
for (psize = 128; ; psize *= 2)
{
char buf[psize];
INTERNAL_SYSCALL_DECL (err);
res = INTERNAL_SYSCALL (sched_getaffinity, err, 3, tid, psize, buf);
if (INTERNAL_SYSCALL_ERROR_P (res, err))
{
if (INTERNAL_SYSCALL_ERRNO (res, err) != EINVAL)
return INTERNAL_SYSCALL_ERRNO (res, err);
}
else
break;
}
if (res != 0)
__kernel_cpumask_size = res;
return 0;
}
int
__pthread_setaffinity_new (pthread_t th, size_t cpusetsize,
const cpu_set_t *cpuset)
{
const struct pthread *pd = (const struct pthread *) th;
INTERNAL_SYSCALL_DECL (err);
int res;
if (__glibc_unlikely (__kernel_cpumask_size == 0))
{
res = __determine_cpumask_size (pd->tid);
if (res != 0)
return res;
}
/* We now know the size of the kernel cpumask_t. Make sure the user
does not request to set a bit beyond that. */
for (size_t cnt = __kernel_cpumask_size; cnt < cpusetsize; ++cnt)
if (((char *) cpuset)[cnt] != '\0')
/* Found a nonzero byte. This means the user request cannot be
fulfilled. */
return EINVAL;
res = INTERNAL_SYSCALL (sched_setaffinity, err, 3, pd->tid, cpusetsize,
cpuset);