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/* $OpenBSD: test-deadlock.c,v 1.1 2020/12/03 19:16:57 anton Exp $ */
/*
* Copyright (c) 2020 Anton Lindqvist <anton@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/param.h> /* PAGE_SIZE */
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include "extern.h"
static void growshrink(const char *);
static void writer(const char *, int);
static int npages = 2;
/*
* Trigger a deadlock between uvn_flush() and uvn_io() caused by uvn_flush()
* holding the vnode lock while waiting for pages to become unbusy; the busy
* pages are allocated and marked as busy by uvn_io() which in turn is trying to
* lock the same vnode while populating the page(s) using I/O on the vnode.
*/
int
test_deadlock(struct context *ctx)
{
int killpip[2];
int status;
pid_t pid;
if (pipe2(killpip, O_NONBLOCK) == -1)
err(1, "pipe2");
pid = fork();
if (pid == -1)
err(1, "fork");
if (pid == 0) {
close(killpip[1]);
writer(ctx->c_path, killpip[0]);
return 0;
}
close(killpip[0]);
fprintf(stderr, "parent = %d, child = %d\n", getpid(), pid);
for (;;) {
if (ctx_abort(ctx))
break;
growshrink(ctx->c_path);
}
/* Signal shutdown to writer() process. */
write(killpip[1], "X", 1);
close(killpip[1]);
if (waitpid(pid, &status, 0) == -1)
err(1, "waitpid");
if (WIFSIGNALED(status))
return 128 + WTERMSIG(status);
if (WIFEXITED(status))
return WEXITSTATUS(status);
return 0;
}
static void
growshrink(const char *path)
{
char *p;
int fd;
/*
* Open and truncate the file causing uvn_flush() to try evict pages
* which are currently being populated by the writer() process.
*/
fd = open(path, O_RDWR | O_TRUNC);
if (fd == -1)
err(1, "open: %s", path);
/* Grow the file again. */
if (ftruncate(fd, npages * PAGE_SIZE) == -1)
err(1, "ftruncate");
p = mmap(NULL, npages * PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, 0);
if (p == MAP_FAILED)
err(1, "mmap");
/* Populate the last page. */
memset(&p[(npages - 1) * PAGE_SIZE], 'x', PAGE_SIZE);
if (munmap(p, npages * PAGE_SIZE) == -1)
err(1, "munmap");
close(fd);
}
static void
writer(const char *path, int killfd)
{
char *p;
int fd;
char c;
fd = open(path, O_RDONLY);
if (fd == -1)
err(1, "open: %s", path);
p = mmap(NULL, npages * PAGE_SIZE, PROT_READ, MAP_SHARED,
fd, 0);
if (p == MAP_FAILED)
err(1, "mmap");
for (;;) {
const struct iovec *iov = (const struct iovec *)p;
if (read(killfd, &c, 1) == 1)
break;
/*
* This write should never succeed since the file descriptor is
* invalid. However, it should cause a page fault during
* copyin() which in turn will invoke uvn_io() while trying to
* populate the page. At this point, it will try to lock the
* vnode, which is potentially already locked by the
* growshrink() process.
*/
pwritev(-1, iov, 1, 0);
}
}
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