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Date:      Sun, 23 Sep 2007 15:51:15 GMT
From:      Karl Andersson <karland@gmail.com>
To:        freebsd-gnats-submit@FreeBSD.org
Subject:   kern/116583: System freezes for short time when using mmap on full filesystem
Message-ID:  <200709231551.l8NFpFmm091779@www.freebsd.org>
Resent-Message-ID: <200709231600.l8NG07p5092880@freefall.freebsd.org>
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>Number:         116583
>Category:       kern
>Synopsis:       System freezes for short time when using mmap on full filesystem
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Sep 23 16:00:07 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Karl Andersson
>Release:        FreeBSD 6.2-RELEASE-p7 i386
>Organization:
>Environment:
FreeBSD tiron.iiice.net 6.2-RELEASE-p7 FreeBSD 6.2-RELEASE-p7 #1: Thu Se
p 20 17:12:47 CEST 2007 i386
>Description:
When trying to write to a memorymapped file on a filesystem that is full the sys
tem locks up as the syncer tries to put the page on disk.
As far as I can see there is no error returned to the userapplication when runin
g msync, so there is no way for the application to know that something is wrong.

The logs fill up with:

Sep 23 17:23:44 tiron kernel: pid 25573 (mmap_testing), uid 0 inumber 4 on /tmp/
mnt: filesystem full
Sep 23 17:23:44 tiron kernel: vnode_pager_putpages: I/O error 28
Sep 23 17:23:44 tiron kernel: vnode_pager_putpages: residual I/O 32768 at 4512
Sep 23 17:23:44 tiron kernel: pid 25573 (mmap_testing), uid 0 inumber 4 on /tmp/
mnt: filesystem full
Sep 23 17:23:44 tiron kernel: vnode_pager_putpages: I/O error 28
Sep 23 17:23:44 tiron kernel: vnode_pager_putpages: residual I/O 65536 at 5003

The problem resulted in a server being almost inaccessable.

>How-To-Repeat:
Using the following code on a filesystem with less then 20MB free space.
(Could be a memorydisk/vnodedisk)

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

int main(int argc, char** argv)
{
    int fp;
    void *p;
    size_t len = 90 * 1024 * 1024;
    int ret;

    fp = open(argv[1], O_RDWR);
    if(fp == 0) {
        perror("open failed");
        exit(1);
    }

    p = mmap(NULL, len, PROT_WRITE | PROT_READ, MAP_SHARED, fp, 0);
    if(p == NULL) {
        perror("mmap failed");
        exit(2);
    }

    // write at least 20MB of data
    const size_t bufsize = 1024*1024;
    char buf[bufsize];

    for(int i = 0; i < bufsize; i++) {
        buf[i] = rand();
    }

    for(int i = 0; i < 25; i++) {
        printf("memcpy(%p + %i = %p, %p, %d)\n",
               p, i * bufsize, p + i * bufsize, buf, bufsize);
        memcpy(p + i * bufsize, buf, bufsize);
    }

    printf("syncing pages\n");
    ret = msync(p, 0, MS_SYNC);
    if(ret != 0) {
        perror("msync failed");
        exit(3);
    }

    ret = munmap(p, len);
    if(ret != 0) {
        perror("munmap failed");
        exit(3);
    }

    ret = close(fp);
    if(ret != 0) {
        perror("fclose failed");
        exit(4);
    }
   
    return 0;
}


>Fix:
Possibly letting msync return an error when the disk is full, or not having sync
er sync at so low prio.


>Release-Note:
>Audit-Trail:
>Unformatted:

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