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    SubjectRe: [PATCH] /proc/kcore: fix seeking
    On Wed, Jan 12, 2011 at 12:04:37AM +0800, Américo Wang wrote:
    > On Mon, Jan 10, 2011 at 09:42:29AM -0500, Dave Anderson wrote:
    > >From: Dave Anderson <anderson@redhat.com>
    > >
    > >Commit 34aacb2920667d405a8df15968b7f71ba46c8f18
    > >("procfs: Use generic_file_llseek in /proc/kcore")
    > >broke seeking on /proc/kcore. This changes it back
    > >to use default_llseek in order to restore the original
    > >behavior.
    > >
    > >The problem with generic_file_llseek is that it only
    > >allows seeks up to inode->i_sb->s_maxbytes, which is
    > >2GB-1 on procfs, where the memory file offset values in
    > >the /proc/kcore PT_LOAD segments may exceed or start
    > >beyond that offset value.
    > >
    >
    > Is the race solved? Using default_llseek() still races
    > with read_kcore() on fpos, AFAIK.

    Hmm, how does it race there?

    read_kcore() manipulates fpos, which can't be changed behind
    us inside the read callback as it's a snapshot. Also read_kcore()
    can change the value of fpos, which is writed back to file->fpos
    from sys_read().

    So the last resulting race here the natural one between
    seeking and reading, which is up to the user to take care
    of.

    Or am I missing something?
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