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DragonFly bugs List (threaded) for 2012-08
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[DragonFlyBSD - Bug #2364] (In Progress) panic: lockmgr: locking against myself

From: Matthew Dillon via Redmine <bugtracker-admin@xxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 16 Aug 2012 17:06:11 -0700

Issue #2364 has been updated by Matthew Dillon.

Status changed from New to In Progress

Here is a better test program, works for x86-64 or i386.  The size of the file depends on how UFS was formatted.  The file must be such that the last block is a fragment which covers less than a page.  We then issue a write that hits that fragment.  The bread() of the buffer brings in the VM page but the VM page's valid bits are not fully set.  This then causes the copyin or copyout to fault, creating the double-lock.

 * Must be one fragment less than a page.  Typical UFS filesystems
 * are configured 1K/8K or 2K/16K.  Larger ones tend to be configured
 * 2K/16K.  Use 7168 for 1K/8K and 6144 for 2K/16K
 * dd if=/dev/zero of=test bs=6144 count=1
 * dd if=/dev/zero of=test bs=7168 count=1
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>

main(int argc, char **argv)
        int fd;
        int backup_fd;
        char *mmap_region;
        char buf[8192];
        int i0, i;
        ssize_t n;

        fd = open(argv[1], O_RDWR);
        mmap_region = mmap(NULL, 16384 * 2,
                fd, 0);
        fprintf(stderr, "%d %p\n", fd, mmap_region);
#if 1
        madvise(mmap_region, 16384 * 2, MADV_RANDOM);
        madvise(mmap_region, 16384 * 2, MADV_INVAL);
        mmap_region[4] = 'b';
        lseek(fd, 0, SEEK_SET);
        n = write(fd, mmap_region, 4096+2048);
        printf("write n=%zd\n", n);
        munmap(mmap_region, 16384 * 2);

Bug #2364: panic: lockmgr: locking against myself

Author: John Marino
Status: In Progress
Priority: High
Assignee: Venkatesh Srinivas
Target version: 

This is an easily repeatable panic.
Edit a file with size > 4096 bytes using /usr/pkg/bin/heme, and save.


Seen on i386 on Virtualbox but already reproduced independently by vrinivas.
DragonFly a4d7a8c-DEVELOPMENT #4: Mon May 7 18:55:28 CEST 2012 root@:/usr/obj/usr/src/sys/GENERIC

core dump located in leaf ~marino/crash

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