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    SubjectRe: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM
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    On Thu, 2011-05-26 at 17:59 +0200, Peter Zijlstra wrote:
    > On Thu, 2011-05-26 at 17:45 +0200, Oleg Nesterov wrote:
    > > Stupid question. Can't we fix this problem if we do
    > >
    > > - if (p == current)
    > > + if (cpu == raw_smp_processor_id())
    > >
    > > ?
    > >
    > > I forgot the rules... but iirc task_cpu(p) can't be changed under us?
    >
    > Easy enough to test.. brain gave out again,. hold on ;-)

    The below seems to run all-right so far, I'll let it run for a while.

    ---
    arch/x86/include/asm/system.h | 2 ++
    kernel/sched.c | 3 ++-
    kernel/sched_debug.c | 7 +++++++
    3 files changed, 11 insertions(+), 1 deletions(-)

    diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
    index c2ff2a1..2c597e8 100644
    --- a/arch/x86/include/asm/system.h
    +++ b/arch/x86/include/asm/system.h
    @@ -10,6 +10,8 @@
    #include <linux/kernel.h>
    #include <linux/irqflags.h>

    +#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
    +
    /* entries in ARCH_DLINFO: */
    #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64)
    # define AT_VECTOR_SIZE_ARCH 2
    diff --git a/kernel/sched.c b/kernel/sched.c
    index 2d12893..f3627e5 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
    * to spin on ->on_cpu if p is current, since that would
    * deadlock.
    */
    - if (p == current) {
    + if (cpu == smp_processor_id()) {
    + p->sched_contributes_to_load = 0;
    ttwu_queue(p, cpu);
    goto stat;
    }
    diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
    index a6710a1..f0ff1de 100644
    --- a/kernel/sched_debug.c
    +++ b/kernel/sched_debug.c
    @@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v)
    (int)strcspn(init_utsname()->version, " "),
    init_utsname()->version);

    +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
    + SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n");
    +#endif
    +#ifdef __ARCH_WANT_UNLOCKED_CTXSW
    + SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n");
    +#endif
    +
    #define P(x) \
    SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x))
    #define PN(x) \



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