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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
46 lines
1.7 KiB
C
46 lines
1.7 KiB
C
/* Low-level thread creation for NPTL. Stub version.
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Copyright (C) 2014-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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/* See the comments in pthread_create.c for the requirements for these
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two macros and the create_thread function. */
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#define START_THREAD_DEFN \
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static void __attribute__ ((noreturn)) start_thread (void)
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#define START_THREAD_SELF THREAD_SELF
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static int
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create_thread (struct pthread *pd, const struct pthread_attr *attr,
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bool *stopped_start, STACK_VARIABLES_PARMS, bool *thread_ran)
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{
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/* If the implementation needs to do some tweaks to the thread after
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it has been created at the OS level, it can set STOPPED_START here. */
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pd->stopped_start = *stopped_start;
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if (__glibc_unlikely (*stopped_start))
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/* See CONCURRENCY NOTES in nptl/pthread_create.c. */
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lll_lock (pd->lock, LLL_PRIVATE);
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return ENOSYS;
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/* It's started now, so if we fail below, we'll have to cancel it
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and let it clean itself up. */
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*thread_ran = true;
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return 0;
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}
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