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The commit documents the ownership rules around 'struct pthread' and when a thread can read or write to the descriptor. With those ownership rules in place it becomes obvious that pd->stopped_start should not be touched in several of the paths during thread startup, particularly so for detached threads. In the case of detached threads, between the time the thread is created by the OS kernel and the creating thread checks pd->stopped_start, the detached thread might have already exited and the memory for pd unmapped. As a regression test we add a simple test which exercises this exact case by quickly creating detached threads with large enough stacks to ensure the thread stack cache is bypassed and the stacks are unmapped. Before the fix the testcase segfaults, after the fix it works correctly and completes without issue. For a detailed discussion see: https://www.sourceware.org/ml/libc-alpha/2017-01/msg00505.html
74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
/* Copyright (C) 2002-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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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 <errno.h>
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#include <string.h>
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#include "pthreadP.h"
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#include <lowlevellock.h>
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int
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__pthread_getschedparam (pthread_t threadid, int *policy,
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struct sched_param *param)
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{
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struct pthread *pd = (struct pthread *) threadid;
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/* Make sure the descriptor is valid. */
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if (INVALID_TD_P (pd))
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/* Not a valid thread handle. */
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return ESRCH;
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int result = 0;
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/* See CREATE THREAD NOTES in nptl/pthread_create.c. */
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lll_lock (pd->lock, LLL_PRIVATE);
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/* The library is responsible for maintaining the values at all
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times. If the user uses an interface other than
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pthread_setschedparam to modify the scheduler setting it is not
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the library's problem. In case the descriptor's values have
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not yet been retrieved do it now. */
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if ((pd->flags & ATTR_FLAG_SCHED_SET) == 0)
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{
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if (__sched_getparam (pd->tid, &pd->schedparam) != 0)
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result = 1;
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else
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pd->flags |= ATTR_FLAG_SCHED_SET;
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}
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if ((pd->flags & ATTR_FLAG_POLICY_SET) == 0)
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{
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pd->schedpolicy = __sched_getscheduler (pd->tid);
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if (pd->schedpolicy == -1)
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result = 1;
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else
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pd->flags |= ATTR_FLAG_POLICY_SET;
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}
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if (result == 0)
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{
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*policy = pd->schedpolicy;
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memcpy (param, &pd->schedparam, sizeof (struct sched_param));
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}
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lll_unlock (pd->lock, LLL_PRIVATE);
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return result;
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}
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strong_alias (__pthread_getschedparam, pthread_getschedparam)
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