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Subjectpage->mapping == NULL recreated without vmware...
Hi,
month ago I informed here that VMware causes oops on exit.
After some time, and tons of tweaking I was able to recreate
it without vmmon... 2.4.0-test9, no special patches, no
vmware modules loaded...

Machine is dual PIII/450, 256MB RAM, 18GB IDE disk.

Here it is... Adjust MSIZE so that it is almost all of your
memory, to cause swapping... (0x0E000000 is for mine 256MB).

/*
Makefile:

CFLAGS = -W -Wall -O2 -D_GNU_SOURCE -D_BSD_SOURCE

oopsdemo: oopsdemo.c
*/

#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/ioctl.h>
#include <sys/raw.h>

unsigned char zero;

#define MSIZE 0x0E000000

int mfd;

void x4768(void) {
int fd;
pid_t pid;
int x4778_1[2];
int x4778_2[2];
int x4779_1[2];
int x4779_2[2];
int from4778;
int to4778;
int from4779;
int to4779;
char* mma[65536];
unsigned int mml[65536];
unsigned int mmi = 0;
unsigned int ln = 0;
unsigned int x;

#define MAL2(a,l) ftruncate(fd, ln+l); mml[mmi] = l; mma[mmi++] = mmap(a, l, PROT_READ|PROT_WRITE, MAP_SHARED, fd, ln); ln += l; mma[mmi-1][0] = 99;
#define MAL(l) MAL2(NULL,l)

fd = open("ram0", O_RDWR | O_CREAT, 0600);
unlink("ram0");
MAL(MSIZE);
pipe(x4778_1);
pipe(x4778_2);
pid = fork();
if (!pid) {
int from4768 = x4778_1[0];
int to4768 = x4778_2[1];
close(x4778_1[1]);
close(x4778_2[0]);
close(fd);
read(from4768, &zero, 1);
#if 1
for (x = 0; x < mml[mmi - 1]; x += 4096)
mma[mmi-1][x] = 98;
#endif
write(to4768, &zero, 1);
read(from4768, &zero, 1);
read(mfd, mma[mmi - 1], mml[mmi - 1]);
printf("1a: %02X\n", mma[mmi-1][0]);
fflush(stdout);
mma[mmi-1][0] = 99;
printf("1b: %02X\n", mma[mmi-1][0]);
/* well, now we have it... */
#if 1
{ char* p; int fda;
fda = open("/dev/zero", O_RDONLY);
p = mmap(NULL, MSIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
for (x = 0; x < MSIZE; x += 4096)
p[x] = 97;
close(fda);
}
#endif

exit(0);

} else if (pid < 0) {
perror("fork failed");
exit(222);
}
to4778 = x4778_1[1];
from4778 = x4778_2[0];
close(x4778_1[0]);
close(x4778_2[1]);

#if 1
pipe(x4779_1);
pipe(x4779_2);
pid = fork();
if (!pid) {
int from4768 = x4779_1[0];
int to4768 = x4779_2[1];
close(x4779_1[1]);
close(x4779_2[0]);
close(to4778);
close(from4778);
close(fd);
read(from4768, &zero, 1);
#if 0
for (x = 0; x < mml[mmi - 1]; x += 4096)
mma[mmi-1][x] = 96;
#endif
write(to4768, &zero, 1);
read(from4768, &zero, 1);
read(mfd, mma[mmi - 1], mml[mmi - 1]);
printf("2a: %02X\n", mma[mmi-1][0]);
fflush(stdout);
mma[mmi-1][0] = 95;
printf("2b: %02X\n", mma[mmi-1][0]);
exit(0);

} else if (pid < 0) {
perror("fork failed");
exit(222);
}
to4779 = x4779_1[1];
from4779 = x4779_2[0];
close(x4779_1[0]);
close(x4779_2[1]);
#else
/* so that read/write to this fails... */
from4779 = -1;
to4779 = -1;
#endif
{
write(to4778, &zero, 1);
write(to4779, &zero, 1);
read(from4778, &zero, 1);
read(from4779, &zero, 1);

write(to4778, &zero, 1);
write(to4779, &zero, 1);
sleep(5);
ftruncate(fd, 0);
}
close(fd);
while (mmi--) {
munmap(mma[mmi], mml[mmi]);
}
exit(0);
}

int main(int argc, char* argv[]) {
struct stat stb;
int q;
char rawsubdev[100];
int min;

if (argc < 2) {
fprintf(stderr, "testit /dev/hda\n");
return 97;
}
q = stat(argv[1], &stb);
if (q != 0) {
fprintf(stderr, "%s: Cannot stat: %m\n", argv[1]);
return 98;
}
q = open("/dev/raw", O_RDWR);
if (q == -1) {
if (errno == ENOENT) {
q = mknod("/dev/raw", S_IFCHR | 0600, makedev(RAW_MAJOR, 0));
if (q != -1) {
q = open("/dev/raw", O_RDWR);
}
}
if (q == -1) {
perror("Opening /dev/raw");
exit(99);
}
}
for (min = 1; min < 256; min++) {
struct raw_config_request rcr;
int err;

rcr.raw_minor = min;
rcr.block_major = major(stb.st_rdev);
rcr.block_minor = minor(stb.st_rdev);
err = ioctl(q, RAW_SETBIND, &rcr);
if (!err)
break;
if (errno != EBUSY) {
fprintf(stderr, "Unexpected error from mapping raw %d: ioctl: %m\n", min);
}
}
if (min >= 256) {
close(q);
fprintf(stderr, "No usable raw device found...\n");
return 97;
}
sprintf(rawsubdev, "/dev/raw%u", min);
mfd = open(rawsubdev, O_RDONLY);
if (mfd == -1) {
if (errno == ENOENT) {
mfd = mknod(rawsubdev, S_IFCHR | 0600, makedev(RAW_MAJOR, min));
if (mfd != -1) {
mfd = open(rawsubdev, O_RDWR);
}
}
if (mfd == -1) {
fprintf(stderr, "Opening %s: %m\n", rawsubdev);
exit(99);
}
}

printf("Go\n");

mlockall(MCL_CURRENT); /* so we do not swap out code, so
signaling through pipes works as
expected... */

x4768();
close(mfd);
close(q);
return 0;
}

If I started it 'strace -f -o logx -r ./oopsdemo /dev/hda', I was awarded with

Go
Process 30900 attached
Process 30901 attached
2a: 33
1a: 33
1b: 63
Process 30900 detached
Process 30901 detached

(well, it looks like that my HDD is still bootable, so write probably went
into wastebasket... erm, I opened /dev/raw1 with O_RDONLY. How is it possible
that I could even create PROT_READ|PROT_WRITE, MAP_SHARED mmapping ? )

Looks strange, isn't it? Both processes could read memory, and first process
could even write to its memory - even after read() failed due to vmtruncate...
and as first process caused to swap everything from memory (touching /dev/zero
mmaped pages), logfile filled up with

page->mapping == NULL

(caused by filemap_swap_out... without patch (see url below) you'll get nice
oops)

Other failure mode is -EIO or page->mapping == NULL in filemap_write_page, when
invoked through do_exit -> ... -> filemap_sync -> ... -> filemap_write_page.

For other details, look at http://platan.vc.cvut.cz/listit. From my findings it
looks to me like that it have something to do with holding page reference
while vmtruncate runs, but I know nothing... You can try playing with #if [01]
to get different failure modes...

I know, only root can do operations with /dev/raw, but... I'm not sure that you
have to play with raw devices to cause this problem... There are other places
which increment page->count temporarily... Or what's wrong...
Best regards,
Petr Vandrovec
vandrove@vc.cvut.cz

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