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    Subject2.6.22-rc5-yesterdaygit with VM debug: BUG in mm/rmap.c:66: anon_vma_link ?
    Hello,
    to catch some memory corruption bug in our code I've modified malloc
    to do mmap + mprotect - which has unfortunate effect that it creates
    thousands and thousands of VMAs. Everything works (though rather slowly
    on kernel with CONFIG_VM_DEBUG) until application does fork() - kernel
    crashes on fork() because copy_process()'s anon_vma_link complains that
    it could not find anon vma after walking through 100000 elements of anon
    list - which seems strange, as I did not touch system wide limit (which
    is 65536 vmas), and mprotect()s started failing after creating 65536
    vmas, as expected.

    Full output of test program and full kernel dmesg are at
    http://buk.vc.cvut.cz/linux/rmap.
    Thanks,
    Petr Vandrovec


    #include <sys/mman.h>
    #include <stdio.h>
    #include <unistd.h>
    #include <fcntl.h>

    #define TRY_REGIONS 131072

    int main(void) {
    unsigned char* ptr[TRY_REGIONS];
    int i;
    int fd;
    int badmprot = 0;
    char buf[16384];
    ssize_t l;

    printf("PID=%u\n", getpid());
    for (i = 0; i < TRY_REGIONS; i++) {
    ptr[i] = mmap(0, 8192, PROT_READ | PROT_WRITE, MAP_PRIVATE |
    MAP_ANONYMOUS, -1, 0);
    if (ptr[i] == MAP_FAILED) {
    break;
    }
    if (mprotect(ptr[i] + 4096, 4096, PROT_NONE)) {
    badmprot++;
    }
    }
    printf("Allocated %u regions, %u mprotects failed\n", i, badmprot);
    fflush(stdout);
    fd = open("/proc/self/maps", O_RDONLY);
    while ((l = read(fd, buf, sizeof buf)) > 0) {
    write(1, buf, l);
    }
    close(fd);
    fork();
    return 0;
    }

    PID=6101
    Allocated 131072 regions, 98310 mprotects failed
    08048000-08049000 r-xp 00000000 08:05 1163513
    /root/test
    08049000-0804a000 rw-p 00000000 08:05 1163513
    /root/test
    b7e37000-e7e44000 rw-p b7e37000 00:00 0
    e7e44000-e7e45000 ---p e7e44000 00:00 0
    e7e45000-e7e46000 rw-p e7e45000 00:00 0
    [65525 lines removed]
    f7f7b000-f7f7c000 ---p f7f7b000 00:00 0
    f7f7c000-f7f7f000 rw-p f7f7c000 00:00 0
    f7f7f000-f7f9a000 r-xp 00000000 08:05 15581230
    /lib/ld-2.5.so
    f7f9a000-f7f9c000 rw-p 0001b000 08:05 15581230
    /lib/ld-2.5.so
    ff869000-ff8ef000 rw-p ff869000 00:00 0
    [stack]
    ffffe000-fffff000 r-xp ffffe000 00:00 0
    [vdso]

    ------------[ cut here ]------------
    kernel BUG at /usr/src/linus/linux-2.6.22-rc5-7515/mm/rmap.c:66!
    invalid opcode: 0000 [1] PREEMPT SMP
    CPU 0
    Modules linked in: binfmt_misc rfcomm l2cap nfs nfsd exportfs lockd
    nfs_acl sunrpc ipx p8022 psnap llc p8023 ppdev lp af_packet aoe deflate
    zlib_deflate zlib_inflate twofish twofish_common camellia serpent
    blowfish des cbc ecb blkcipher aes xcbc sha256 sha1 crypto_null hmac
    crypto_hash cryptomgr af_key nls_utf8 nls_iso8859_2 ntfs fuse sbp2 loop
    hci_usb raw1394 dv1394 bluetooth usb_storage usbhid libusual
    snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm snd_timer firewire_ohci
    firewire_core sg snd crc_itu_t parport_pc parport sky2 k8temp 8250_pnp
    8250 serial_core sr_mod serio_raw hwmon sata_sil24 ohci1394 ieee1394
    ohci_hcd ehci_hcd cdrom snd_page_alloc usbcore i2c_nforce2
    Pid: 6101, comm: test Not tainted 2.6.22-rc5-7515-64 #1
    RIP: 0010:[<ffffffff802987bb>] [<ffffffff802987bb>] anon_vma_link+0x8b/0xa0
    RSP: 0018:ffff810111d4fd88 EFLAGS: 00010202
    RAX: ffff8101109fb9e0 RBX: ffff8101109fb978 RCX: ffff8101109fb978
    RDX: ffff810112fccf10 RSI: 00000000000186a1 RDI: 0000000000000000
    RBP: ffff810111d4fd98 R08: ffff810112fccf10 R09: 0000000000000000
    R10: ffffffff8029874b R11: 0000000000000000 R12: ffff810112fccee0
    R13: 0000000001200011 R14: ffff810111590080 R15: ffff810111590080
    FS: 0000000000000000(0000) GS:ffffffff80652000(0063) knlGS:00000000f7e196c0
    CS: 0010 DS: 002b ES: 002b CR0: 000000008005003b
    CR2: 00000000f7eaa7c0 CR3: 0000000111c17000 CR4: 00000000000006e0
    Process test (pid: 6101, threadinfo ffff810111d4e000, task ffff810112fcf080)
    Stack: 0000000000000001 ffff8101109fb978 ffff810111d4fe78 ffffffff8023817c
    ffffffff8061d688 ffff8101140e00e0 ffff8101115901b8 ffff81012560d148
    ffff8101115906a0 ffff810111ebd760 00000000f7e19708 0000000000000000
    Call Trace:
    [<ffffffff8023817c>] copy_process+0xb9c/0x1760
    [<ffffffff8024dd72>] alloc_pid+0x212/0x320
    [<ffffffff80238ed3>] do_fork+0xa3/0x290
    [<ffffffff804c6880>] _spin_unlock+0x30/0x60
    [<ffffffff802aebb6>] __fput+0x176/0x1c0
    [<ffffffff80227ce7>] sys32_clone+0x27/0x30
    [<ffffffff802279d5>] ia32_ptregs_common+0x25/0x50


    Code: 0f 0b eb fe 0f 0b eb fe 66 0f 1f 44 00 00 0f 1f 80 00 00 00
    RIP [<ffffffff802987bb>] anon_vma_link+0x8b/0xa0
    RSP <ffff810111d4fd88>
    note: test[6101] exited with preempt_count 1
    -
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