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    SubjectRe: [PATCH] Fix a race in pid generation that causes pids to be reused immediately.
    On Mon, Jun 14, 2010 at 04:58:51PM -0700, Andrew Morton wrote:
    > Using
    >
    > grep -r '[ ]cmpxchg[^_]' . | grep -v /arch/
    >
    > I can't see any cmpxchg() callers in truly generic code. lockdep and
    > kernel/trace/ring_buffer.c aren't used on the more remote
    > architectures, I think.

    What about:

    drivers/gpu/drm/drm_lock.c: prev = cmpxchg(lock, old, new);
    kernel/lockdep.c: n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->de
    kernel/sched_clock.c: if (cmpxchg64(&scd->clock, old_clock, clock) != old_cloc
    fs/btrfs/inode.c: if (cmpxchg(&root->orphan_cleanup_state, 0, ORPHAN_CLEAN
    fs/ext4/inode.c: } while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl

    The last is quite new --- I had just recently done a similar set of
    research as you did before accepting the patch that added cmpxchg into
    ext4 (during the last merge window), and I thought cmpxchg() had
    entered the "supported by all architectures" category. It looked like
    it had only recently reached state, but I had reached the conclusion
    that it was safe to use.

    - Ted


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