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    SubjectRe: [PATCH -mm] ehca: avoid crash on kthread_create() failure
    On Mon, Dec 25, 2006 at 05:30:23PM +0900, Akinobu Mita wrote:
    > On Mon, Dec 25, 2006 at 05:12:57PM +0900, Akinobu Mita wrote:
    > > Index: 2.6-mm/drivers/infiniband/hw/ehca/ehca_irq.c
    > > ===================================================================
    > > --- 2.6-mm.orig/drivers/infiniband/hw/ehca/ehca_irq.c
    > > +++ 2.6-mm/drivers/infiniband/hw/ehca/ehca_irq.c
    > > @@ -606,13 +606,16 @@ static int comp_task(void *__cct)
    > > static struct task_struct *create_comp_task(struct ehca_comp_pool *pool,
    > > int cpu)
    > > {
    > > + struct task_struct *task;
    > > struct ehca_cpu_comp_task *cct;
    > >
    > > cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
    > > spin_lock_init(&cct->task_lock);
    > > INIT_LIST_HEAD(&cct->cq_list);
    > > init_waitqueue_head(&cct->wait_queue);
    > > - cct->task = kthread_create(comp_task, cct, "ehca_comp/%d", cpu);
    > > + task = kthread_create(comp_task, cct, "ehca_comp/%d", cpu);
    > > + if (!IS_ERR(task))
    > > + cct->task = task;
    > >
    > > return cct->task;
    > > }
    >
    > This patch is wrong. It changes to make create_comp_task() return NULL
    > on failure.
    >
    > (BTW, all these ehca fixes are not compile tested due to luck of
    > cross comile environment)
    >
    > Subject: [PATCH -mm] ehca: avoid crash on kthread_create() failure (v2)
    >
    > This patch disallows invalid task_struct pointer returned by
    > kthread_create() to be written to percpu data to avoid crash.
    >
    > Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    > Cc: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
    > Cc: Christoph Raisch <raisch@de.ibm.com>
    > Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
    >
    > ---
    > drivers/infiniband/hw/ehca/ehca_irq.c | 11 ++++++++---
    > 1 file changed, 8 insertions(+), 3 deletions(-)
    >
    > Index: 2.6-mm/drivers/infiniband/hw/ehca/ehca_irq.c
    > ===================================================================
    > --- 2.6-mm.orig/drivers/infiniband/hw/ehca/ehca_irq.c
    > +++ 2.6-mm/drivers/infiniband/hw/ehca/ehca_irq.c
    > @@ -606,15 +606,18 @@ static int comp_task(void *__cct)
    > static struct task_struct *create_comp_task(struct ehca_comp_pool *pool,
    > int cpu)
    > {
    > + struct task_struct *task;
    > struct ehca_cpu_comp_task *cct;
    >
    > cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
    > spin_lock_init(&cct->task_lock);
    > INIT_LIST_HEAD(&cct->cq_list);
    > init_waitqueue_head(&cct->wait_queue);
    > - cct->task = kthread_create(comp_task, cct, "ehca_comp/%d", cpu);
    > + task = kthread_create(comp_task, cct, "ehca_comp/%d", cpu);
    > + if (!IS_ERR(task))
    > + cct->task = task;
    >
    > - return cct->task;
    > + return task;
    > }
    >
    > static void destroy_comp_task(struct ehca_comp_pool *pool,
    > @@ -684,8 +687,10 @@ static int comp_pool_callback(struct not
    > case CPU_UP_CANCELED:
    > ehca_gen_dbg("CPU: %x (CPU_CANCELED)", cpu);
    > cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu);
    > - kthread_bind(cct->task, any_online_cpu(cpu_online_map));
    > - destroy_comp_task(pool, cpu);
    > + if (cct->task) {
    > + kthread_bind(cct->task, any_online_cpu(cpu_online_map));
    > + destroy_comp_task(pool, cpu);
    > + }

    This is correct because cct is allocated via alloc_percpu, which in
    turn calls kzalloc, which means cct->task is NULL by default, but it's
    a little too obscure for me. How about making it explicit?

    task = kthread_create(...)
    if (!IS_ERR(task))
    cct->task = task;
    else
    cct->task = NULL;

    return cct->task;

    Cheers,
    Muli
    -
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