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As with many other projects, we use some shmalloc allocator. At some point we need to make a part of allocated pages back private to process. And it should be populated straight away. Check that (MAP_PRIVATE | MAP_POPULATE) actually copies the private page. [akpm@linux-foundation.org: change message, per review discussion] Link: http://lkml.kernel.org/r/20180801233636.29354-1-dima@arista.com Signed-off-by: Dmitry Safonov <dima@arista.com> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Hua Zhong <hzhong@arista.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Stuart Ritchie <sritchie@arista.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
113 lines
2.4 KiB
C
113 lines
2.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (c) 2018 Dmitry Safonov, Arista Networks
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*
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* MAP_POPULATE | MAP_PRIVATE should COW VMA pages.
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*/
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#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <sys/mman.h>
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#include <sys/socket.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#ifndef MMAP_SZ
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#define MMAP_SZ 4096
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#endif
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#define BUG_ON(condition, description) \
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do { \
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if (condition) { \
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fprintf(stderr, "[FAIL]\t%s:%d\t%s:%s\n", __func__, \
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__LINE__, (description), strerror(errno)); \
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exit(1); \
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} \
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} while (0)
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static int parent_f(int sock, unsigned long *smap, int child)
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{
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int status, ret;
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ret = read(sock, &status, sizeof(int));
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BUG_ON(ret <= 0, "read(sock)");
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*smap = 0x22222BAD;
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ret = msync(smap, MMAP_SZ, MS_SYNC);
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BUG_ON(ret, "msync()");
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ret = write(sock, &status, sizeof(int));
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BUG_ON(ret <= 0, "write(sock)");
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waitpid(child, &status, 0);
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BUG_ON(!WIFEXITED(status), "child in unexpected state");
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return WEXITSTATUS(status);
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}
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static int child_f(int sock, unsigned long *smap, int fd)
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{
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int ret, buf = 0;
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smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
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MAP_PRIVATE | MAP_POPULATE, fd, 0);
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BUG_ON(smap == MAP_FAILED, "mmap()");
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BUG_ON(*smap != 0xdeadbabe, "MAP_PRIVATE | MAP_POPULATE changed file");
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ret = write(sock, &buf, sizeof(int));
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BUG_ON(ret <= 0, "write(sock)");
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ret = read(sock, &buf, sizeof(int));
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BUG_ON(ret <= 0, "read(sock)");
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BUG_ON(*smap == 0x22222BAD, "MAP_POPULATE didn't COW private page");
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BUG_ON(*smap != 0xdeadbabe, "mapping was corrupted");
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return 0;
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}
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int main(int argc, char **argv)
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{
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int sock[2], child, ret;
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FILE *ftmp;
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unsigned long *smap;
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ftmp = tmpfile();
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BUG_ON(ftmp == 0, "tmpfile()");
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ret = ftruncate(fileno(ftmp), MMAP_SZ);
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BUG_ON(ret, "ftruncate()");
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smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
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MAP_SHARED, fileno(ftmp), 0);
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BUG_ON(smap == MAP_FAILED, "mmap()");
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*smap = 0xdeadbabe;
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/* Probably unnecessary, but let it be. */
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ret = msync(smap, MMAP_SZ, MS_SYNC);
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BUG_ON(ret, "msync()");
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ret = socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sock);
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BUG_ON(ret, "socketpair()");
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child = fork();
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BUG_ON(child == -1, "fork()");
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if (child) {
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ret = close(sock[0]);
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BUG_ON(ret, "close()");
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return parent_f(sock[1], smap, child);
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}
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ret = close(sock[1]);
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BUG_ON(ret, "close()");
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return child_f(sock[0], smap, fileno(ftmp));
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}
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