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9f0d2c0ee6
popen modifies its file handler book-keeping under a lock that wasn't being taken during fork. This meant that a concurrent popen and fork could end up copying the lock in a "locked" state into the fork child, where subsequently calling popen would lead to a deadlock due to the already (spuriously) held lock. This commit fixes the deadlock by appropriately taking the lock before fork, and releasing/resetting it in the parent/child after the fork. A new test for concurrent popen and fork is also added. It consistently hangs (and therefore fails via timeout) without the fix applied. Reviewed-by: Florian Weimer <fweimer@redhat.com>
81 lines
2.2 KiB
C
81 lines
2.2 KiB
C
/* Test concurrent popen and fork.
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Copyright (C) 2024 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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<https://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <stdatomic.h>
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#include <pthread.h>
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#include <unistd.h>
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#include <sys/wait.h>
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#include <support/check.h>
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#include <support/xthread.h>
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#include <support/xunistd.h>
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static void
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popen_and_pclose (void)
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{
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FILE *f = popen ("true", "r");
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TEST_VERIFY_EXIT (f != NULL);
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pclose (f);
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return;
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}
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static atomic_bool done = ATOMIC_VAR_INIT (0);
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static void *
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popen_and_pclose_forever (__attribute__ ((unused))
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void *arg)
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{
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while (!atomic_load_explicit (&done, memory_order_acquire))
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popen_and_pclose ();
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return NULL;
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}
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static int
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do_test (void)
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{
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/* Repeatedly call popen in a loop during the entire test. */
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pthread_t t = xpthread_create (NULL, popen_and_pclose_forever, NULL);
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/* Repeatedly fork off and reap child processes one-by-one.
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Each child calls popen once, then exits, leading to the possibility
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that a child forks *during* our own popen call, thus inheriting any
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intermediate popen state, possibly including lock state(s). */
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for (int i = 0; i < 100; i++)
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{
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int cpid = xfork ();
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if (cpid == 0)
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{
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popen_and_pclose ();
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_exit (0);
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}
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else
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xwaitpid (cpid, NULL, 0);
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}
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/* Stop calling popen. */
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atomic_store_explicit (&done, 1, memory_order_release);
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xpthread_join (t);
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return 0;
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}
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#include <support/test-driver.c>
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