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    SubjectRe: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones
    On Sun, Oct 9, 2016 at 10:15 AM, Joel Fernandes <joelaf@google.com> wrote:
    > On Fri, Oct 7, 2016 at 10:28 PM, Joel Fernandes <joelaf@google.com> wrote:
    >> If FTRACE_PER_CPU flag is passed to ramoops pdata, split the space into
    >> multiple zones depending on the number of CPUs.
    >>
    >> This speeds up the performance of function tracing by about 280% in my tests as
    >> we avoid the locking. The trade off being lesser space available per CPU. Let
    >> the ramoops user decide which option they want based on pdata flag.
    >>
    >> Signed-off-by: Joel Fernandes <joelaf@google.com>
    >> ---
    >> fs/pstore/ram.c | 70 +++++++++++++++++++++++++++++++++++-----------
    >> include/linux/pstore_ram.h | 3 ++
    >> 2 files changed, 56 insertions(+), 17 deletions(-)
    >>
    >> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
    > [..]
    >> @@ -391,14 +418,21 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
    >> {
    >> int i;
    >>
    >> - if (!cxt->przs)
    >> - return;
    >> + /* Free dump PRZs */
    >> + if (cxt->przs) {
    >> + for (i = 0; i < cxt->max_dump_cnt; i++)
    >> + persistent_ram_free(cxt->przs[i]);
    >>
    >> - for (i = 0; i < cxt->max_dump_cnt; i++)
    >> - persistent_ram_free(cxt->przs[i]);
    >> + kfree(cxt->przs);
    >> + cxt->max_dump_cnt = 0;
    >> + }
    >>
    >> - kfree(cxt->przs);
    >> - cxt->max_dump_cnt = 0;
    >> + /* Free ftrace PRZs */
    >> + if (cxt->fprzs) {
    >> + for (i = 0; i < nr_cpu_ids; i++)
    >> + persistent_ram_free(cxt->przs[i]);
    >
    > I am supposed to free fprzs[i] here, instead of przs[i]. Also need to
    > check flag and free correct number of zones. Will fix for v2, sorry
    > about that.

    I think the cpu id needs to be bounds-checked against the size of the
    allocation. In theory, CPU hot-plug could grow the number of CPUs
    after pstore is initialized.

    -Kees

    --
    Kees Cook
    Nexus Security

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