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    Subject[PATCH] sched: Make cond_resched*() available earlier
    Using early netconsole and gianfar driver this error pops up:

    netconsole: timeout waiting for carrier

    It appears that net/core/netpoll.c:netpoll_setup() is using
    cond_resched() in a loop waiting for a carrier.

    The thing is that cond_resched() is a no-op when system_state !=
    SYSTEM_RUNNING, and so drivers/net/phy/phy.c's state_queue is never
    scheduled, therefore link detection doesn't work.

    The system_state check exists to avoid very early calls to the
    scheduler. Though, using cond_resched() should be safe after scheduler
    is initialized, so instead of checking the system_state, we can test
    that the scheduler is running, therefore making cond_resched() and
    friends available much earlier (but not too much).

    Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
    ---

    On Wed, Jul 08, 2009 at 02:58:46PM +0200, Peter Zijlstra wrote:
    [...]
    > > > > Hm. Speaking of cond_resched*() only, then it should be pretty
    > > > > safe to convert the SYSTEM_RUNNING checks to scheduler_running,
    > > > > no? scheduler_running is set after sched_init().
    > > >
    > > > Hmm, that might work, I'd have to audit sched_init_smp() as it seems to
    > > > do way too much...
    > >
    > > sched_init_smp() is called from the kernel_thread(), so
    > > if the scheduler is not functional prior to kernel_thread(),
    > > you're in trouble anyway, no? The point is that a lot of
    > > code is calling schedule() prior to sched_init_smp()
    > > (e.g. msleep(), mutexes), and there are no issues. So
    > > should be no issues with cond_resched()?
    >
    > Yeah, it should be good, I just got paranoid looking at
    > sched_init_smp().

    OK, thanks everyone for the reviews.

    Here is an updated patch. As usual, tested on UP PowerPC, with and
    without SMP, PREEMPT and PREEMPT_VOLUNTARY.

    kernel/sched.c | 6 +++---
    1 files changed, 3 insertions(+), 3 deletions(-)

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 7c9098d..555360b 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -6561,7 +6561,7 @@ static void __cond_resched(void)
    int __sched _cond_resched(void)
    {
    if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
    - system_state == SYSTEM_RUNNING) {
    + scheduler_running) {
    __cond_resched();
    return 1;
    }
    @@ -6579,7 +6579,7 @@ EXPORT_SYMBOL(_cond_resched);
    */
    int cond_resched_lock(spinlock_t *lock)
    {
    - int resched = need_resched() && system_state == SYSTEM_RUNNING;
    + int resched = need_resched() && scheduler_running;
    int ret = 0;

    if (spin_needbreak(lock) || resched) {
    @@ -6599,7 +6599,7 @@ int __sched cond_resched_softirq(void)
    {
    BUG_ON(!in_softirq());

    - if (need_resched() && system_state == SYSTEM_RUNNING) {
    + if (need_resched() && scheduler_running) {
    local_bh_enable();
    __cond_resched();
    local_bh_disable();
    --
    1.6.3.3


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