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    Subject[tip:perfcounters/core] perf_counter: allow and require one-page mmap on counting counters
    Commit-ID:  bb0ad4e22511e7caa715362945ad0766c7cca37e
    Gitweb: http://git.kernel.org/tip/bb0ad4e22511e7caa715362945ad0766c7cca37e
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Wed, 25 Mar 2009 12:48:31 +0100
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 25 Mar 2009 13:02:54 +0100

    perf_counter: allow and require one-page mmap on counting counters

    A brainfart stopped single page mmap()s working. The rest of the code
    should be perfectly fine with not having any data pages.

    Reported-by: Paul Mackerras <paulus@samba.org>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <1237981712.7972.812.camel@twins>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    kernel/perf_counter.c | 6 +++++-
    1 files changed, 5 insertions(+), 1 deletions(-)

    diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
    index f3e1b27..95e0257 100644
    --- a/kernel/perf_counter.c
    +++ b/kernel/perf_counter.c
    @@ -1369,7 +1369,11 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
    vma_size = vma->vm_end - vma->vm_start;
    nr_pages = (vma_size / PAGE_SIZE) - 1;

    - if (nr_pages == 0 || !is_power_of_2(nr_pages))
    + /*
    + * If we have data pages ensure they're a power-of-two number, so we
    + * can do bitmasks instead of modulo.
    + */
    + if (nr_pages != 0 && !is_power_of_2(nr_pages))
    return -EINVAL;

    if (vma_size != PAGE_SIZE * (1 + nr_pages))

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