reiserfs locking (v2)

From: Sergey Senozhatsky
Date: Fri Jul 02 2010 - 05:45:26 EST

Crap, I forgot to munmap. Sorry.

fixed


=== code ===


/*

2010, Sergey Senozhatsky. GPLv2

Description:
We have several PIDs working with conftest.mmap.
Actually this is (seems) what hapenning during emacs configure.

traced emacs configure:

vfork() ...
====
... PID 5446

5446 open("conftest.mmap", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0600) = 3
write(3,
"g\306isQ\377J\354)\315\272\253\362\373\343F|\302T\370\33\350\347\215vZ.c3\237\311\232"...,
4096) = 4096
close(3) = 0
open("conftest.txt", O_RDWR|O_CREAT|O_TRUNC|O_LARGEFILE, 0600) = 3
write(3, "\0", 1) = 1
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0xb78a8000
close(3) = 0
munmap(0xb78a8000, 4096) = 0
open("conftest.mmap", O_RDWR|O_LARGEFILE) = 3
mmap2(0xb78a8000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED,
3, 0) = 0xb78a8000
read(3,
"*****"...,
4096) = 4096
close(3) = 0

open(".", O_RDONLY|O_LARGEFILE) = 3
close(3) = 0
fstatat64(AT_FDCWD, "conftest.mmap", {st_mode=S_IFREG|0600,
st_size=4096, ...}, AT_SYMLINK_NOFOLLOW) = 0
unlinkat(AT_FDCWD, "conftest.mmap", 0) = 0

====
... PID 5449
5449 fstatat64(AT_FDCWD, "conftest.mmap", {st_mode=S_IFREG|0600, st_size=4096, ...}, AT_SYMLINK_NOFOLLOW) = 0
5449 unlinkat(AT_FDCWD, "conftest.mmap", 0) = 0
5449 execve("/bin/rm", ["rm", "-f", "conftest.mmap", "conftest.txt"]
..
*/

/*
The code below produces:
[ 46.727489] =======================================================
[ 46.727495] [ INFO: possible circular locking dependency detected ]
[ 46.727499] 2.6.35-rc3-dbg-git5-00446-g36336bc-dirty #64
[ 46.727503] -------------------------------------------------------
[ 46.727506] a.out/5840 is trying to acquire lock:
[ 46.727510] (&sb->s_type->i_mutex_key#10){+.+.+.}, at: [<c10f1d5c>] reiserfs_file_release+0x12b/0x367
[ 46.727526]
[ 46.727527] but task is already holding lock:
[ 46.727530] (&mm->mmap_sem){++++++}, at: [<c1092937>] sys_mmap_pgoff+0xa4/0xe7
[ 46.727540]
[ 46.727541] which lock already depends on the new lock.
[ 46.727543]
[ 46.727546]
[ 46.727546] the existing dependency chain (in reverse order) is:
[ 46.727550]
[ 46.727551] -> #1 (&mm->mmap_sem){++++++}:
[ 46.727557] [<c104f566>] lock_acquire+0x59/0x70
[ 46.727565] [<c108cf70>] might_fault+0x53/0x70
[ 46.727571] [<c1185438>] copy_to_user+0x30/0x48
[ 46.727578] [<c10afaf9>] filldir64+0x95/0xc9
[ 46.727584] [<c10f257c>] reiserfs_readdir_dentry+0x35d/0x4d9
[ 46.727590] [<c10f270a>] reiserfs_readdir+0x12/0x17
[ 46.727596] [<c10afd17>] vfs_readdir+0x6d/0x92
[ 46.727600] [<c10afe91>] sys_getdents64+0x63/0xa2
[ 46.727606] [<c10027d3>] sysenter_do_call+0x12/0x32
[ 46.727612]
[ 46.727613] -> #0 (&sb->s_type->i_mutex_key#10){+.+.+.}:
[ 46.727621] [<c104ef5c>] __lock_acquire+0x96d/0xbe1
[ 46.727626] [<c104f566>] lock_acquire+0x59/0x70
[ 46.727632] [<c12c5694>] __mutex_lock_common+0x39/0x36b
[ 46.727639] [<c12c5a00>] mutex_lock_nested+0x12/0x15
[ 46.727644] [<c10f1d5c>] reiserfs_file_release+0x12b/0x367
[ 46.727650] [<c10a5805>] fput+0xe0/0x16a
[ 46.727657] [<c1090c9e>] remove_vma+0x28/0x47
[ 46.727662] [<c1091a60>] do_munmap+0x1e8/0x200
[ 46.727667] [<c109230a>] mmap_region+0x6b/0x372
[ 46.727672] [<c109284d>] do_mmap_pgoff+0x23c/0x282
[ 46.727678] [<c1092950>] sys_mmap_pgoff+0xbd/0xe7
[ 46.727683] [<c10027d3>] sysenter_do_call+0x12/0x32
[ 46.727689]
[ 46.727690] other info that might help us debug this:
[ 46.727691]
[ 46.727695] 1 lock held by a.out/5840:
[ 46.727698] #0: (&mm->mmap_sem){++++++}, at: [<c1092937>] sys_mmap_pgoff+0xa4/0xe7
[ 46.727707]
[ 46.727708] stack backtrace:
[ 46.727713] Pid: 5840, comm: a.out Not tainted 2.6.35-rc3-dbg-git5-00446-g36336bc-dirty #64
[ 46.727717] Call Trace:
[ 46.727722] [<c12c4913>] ? printk+0xf/0x11
[ 46.727728] [<c104dc09>] print_circular_bug+0x8a/0x96
[ 46.727734] [<c104ef5c>] __lock_acquire+0x96d/0xbe1
[ 46.727740] [<c104ccc8>] ? look_up_lock_class+0x6c/0x7b
[ 46.727746] [<c104e462>] ? mark_lock+0x26/0x1b3
[ 46.727752] [<c104f566>] lock_acquire+0x59/0x70
[ 46.727758] [<c10f1d5c>] ? reiserfs_file_release+0x12b/0x367
[ 46.727764] [<c12c5694>] __mutex_lock_common+0x39/0x36b
[ 46.727769] [<c10f1d5c>] ? reiserfs_file_release+0x12b/0x367
[ 46.727775] [<c12c5a00>] mutex_lock_nested+0x12/0x15
[ 46.727781] [<c10f1d5c>] ? reiserfs_file_release+0x12b/0x367
[ 46.727786] [<c10f1d5c>] reiserfs_file_release+0x12b/0x367
[ 46.727792] [<c108d77d>] ? free_pgd_range+0x96/0x12f
[ 46.727798] [<c10a57b5>] ? fput+0x90/0x16a
[ 46.727803] [<c10a5805>] fput+0xe0/0x16a
[ 46.727808] [<c1090c9e>] remove_vma+0x28/0x47
[ 46.727814] [<c1091811>] ? arch_unmap_area_topdown+0x0/0x18
[ 46.727819] [<c1091a60>] do_munmap+0x1e8/0x200
[ 46.727825] [<c109230a>] mmap_region+0x6b/0x372
[ 46.727831] [<c109284d>] do_mmap_pgoff+0x23c/0x282
[ 46.727837] [<c1092950>] sys_mmap_pgoff+0xbd/0xe7
[ 46.727842] [<c10027d3>] sysenter_do_call+0x12/0x32


*/

#define _GNU_SOURCE

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

int main()
{
char buf[4096];
int i = 0;
/* we don't really care */
for (; i < 4096; i++)
buf[i] = (i + 65) % 255;

for (i = 0; i < 10; i++) {

int pid = fork();
if (pid > 0 ) {
printf("parent...");
} else if (pid == 0) {

printf("child...\n");
int fd = open("conftest.mmap", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0600);
if (fd > 0) {
printf("OPEN ok %d\n", fd);
if (write(fd, buf, 4096) < 0)
printf("WRITE error\n");
else
printf("WRITE ok\n");

close(fd);
} else {
printf("OPEN error\n");
}

fd = open("conftest.mmap", O_RDWR|O_LARGEFILE);
if (fd > 0) {
printf("OPEN conftest.mmap %d\n", fd);

void *map = mmap((void*)0xb78a8000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, fd, 0);
if (map == MAP_FAILED) {
printf("MMAP failed\n");
goto out;
} else {
printf("MMAP ok\n");
}

if (read(fd, buf, 4096) < 0)
printf("READ failed\n");
else
printf("READ ok\n");

close(fd);
munmap(map, 4096);
} else {
printf("Error: can't open conftest.mmap\n");
}

out:
fd = open(".", O_RDONLY|O_LARGEFILE);
if (fd > 0) {
printf("OPEN . ok %d... closing\n", fd);
close(fd);
} else {
printf("OPEN error\n");
}

struct stat _stat;
if (fstatat(AT_FDCWD, "conftest.mmap", &_stat, AT_SYMLINK_NOFOLLOW) < 0)
printf("FSTATAT error\n");
else
printf("FSTATAT ok\n");

if (unlinkat(AT_FDCWD, "conftest.mmap", 0) < 0)
printf("UNLINKAT error\n");
else
printf("UNLINKAT ok\n");

} else {
printf("FORK error\n");
}
}

return 0;
}

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