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    SubjectRe: [PATCH] /proc/kcore: fix seeking
    On Tue, Jan 11, 2011 at 05:23:23PM +0100, Frederic Weisbecker wrote:
    >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.

    Hmm, I just read the changelog of commit
    34aacb2920667d405a8df15968b7f71ba46c8f18, which claims to fix
    the race. So anything changed in vfs layer after that?

    Thanks.


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