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    SubjectRe: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop_machine
    Date
    On Wednesday, 12 of November 2008, Rusty Russell wrote:
    > On Tuesday 11 November 2008 21:22:14 Ingo Molnar wrote:
    > > * Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > > > So, it evidently fails while re-enabling the non-boot CPU and not
    > > > during disabling it as I thought before.
    >
    > (Resend, due to HTML version previously)
    >
    > But what is calling stop_machine in that path?
    >
    > There *is* a race, but I don't think it could cause this (we should make a
    > copy of active.fnret inside the lock before returning it).

    Still, that seems to be the case.

    > Two patches: one fixes that race, the next adds debugging spew.
    >
    > stop_machine: fix race with return value

    With this patch applied (reproduced below for clarity) the problem is not
    reproducible any more.

    Care to push it upstream ASAP?

    Thanks,
    Rafael

    ---
    stop_machine: fix race with return value

    We should not access active.fnret outside the lock; in theory the next
    stop_machine could overwrite it.

    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    ---
    kernel/stop_machine.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff -r d7c9a15da615 kernel/stop_machine.c
    --- a/kernel/stop_machine.c Mon Nov 10 09:47:45 2008 +1100
    +++ b/kernel/stop_machine.c Tue Nov 11 23:19:47 2008 +1030
    @@ -112,7 +112,7 @@
    int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
    {
    struct work_struct *sm_work;
    - int i;
    + int i, ret;

    /* Set up initial state. */
    mutex_lock(&lock);
    @@ -137,8 +137,9 @@
    /* This will release the thread on our CPU. */
    put_cpu();
    flush_workqueue(stop_machine_wq);
    + ret = active.fnret;
    mutex_unlock(&lock);
    - return active.fnret;
    + return ret;
    }

    int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)


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