ffs_alloc panic patch

From: Pavel Merdine (fbsdlist_at_merdin.com)
Date: 08/27/04

  • Next message: Antony Mawer: "Re: ffs_alloc panic patch" 
    Date: Fri, 27 Aug 2004 21:52:45 +0400
To: freebsd-stable@freebsd.org

    Hello,

    I'd like to propose the following patch:

    ------------------------------------------------------------------
    --- ffs_alloc.c.orig Fri May 14 19:03:50 2004
    +++ ffs_alloc.c Sat Aug 7 03:36:32 2004
    @@ -712,7 +712,7 @@
                    minbfree = 1;
            cgsize = fs->fs_fsize * fs->fs_fpg;
            dirsize = fs->fs_avgfilesize * fs->fs_avgfpdir;
    - curdirsize = avgndir ? (cgsize - avgbfree * fs->fs_bsize) / avgndir : 0;
    + curdirsize = avgndir ? (cgsize - avgbfree * fs->fs_bsize) / avgndir : 512;
            if (dirsize < curdirsize)
                    dirsize = curdirsize;
            maxcontigdirs = min((avgbfree * fs->fs_bsize) / dirsize, 255);
    ------------------------------------------------------------------

    It should solve the problem of "panic: integer divide fault" on the
    last line of the code above. The panic happens on:
    1. directory creation
    2. when disk is empty
    3. when avg_dir_size avg_file_size are set to values, so
      avg_dir_size * avg_file_size is negative in integer.
      example: avg_dir_size = 8000, avf_file_size = 375000.
    (curdirsize == 0 and dirsize < 0, so dirsize = 0)

    I'm sure it's very old bug.

    I know that maybe those params are wrong. And maybe newfs or tunefs
    should check them.
    But I'm sure that there should be some check in the code above to
    eliminate ANY possibility of panic.
    Panic is VERY undesirable situation. And I'm in doubt why those people
    who wrote ffs like panics so devotedly:

    # grep -c "panic" ffs_alloc.c ffs_softdep.c
    ffs_alloc.c:37
    ffs_softdep.c:108

    I think such things are not acceptable in production environment. Why
    those functions cannot just return a failure state and leave system
    working? 

    -- 
/ Pavel Merdine
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  • Next message: Antony Mawer: "Re: ffs_alloc panic patch"

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