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    SubjectRe: [PATCH v2 5/5] scsi: libsas: fix a race condition when smp task timeout
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    On 19/09/2018 04:32, Jason Yan wrote:
    > When the lldd is processing the complete sas task in interrupt and set
    > the task stat as SAS_TASK_STATE_DONE, the smp timeout timer is able to
    > be triggered at the same time. And smp_task_timedout() will complete the
    > task wheter the SAS_TASK_STATE_DONE is set or not. Then the sas task may
    > freed before lldd end the interrupt process. Thus a use-after-free will
    > happen.
    >
    > Fix this by calling the complete() only when SAS_TASK_STATE_DONE is not
    > set. And remove the check of the return value of the del_timer(). Once
    > the LLDD sets DONE, it must call task->done(), which will call
    > smp_task_done()->complete() and the task will be completed and freed
    > correctly.
    >
    > Reported-by: chenxiang <chenxiang66@hisilicon.com>
    > Signed-off-by: Jason Yan <yanaijie@huawei.com>
    > CC: John Garry <john.garry@huawei.com>
    > CC: Johannes Thumshirn <jthumshirn@suse.de>
    > CC: Ewan Milne <emilne@redhat.com>
    > CC: Christoph Hellwig <hch@lst.de>
    > CC: Tomas Henzl <thenzl@redhat.com>
    > CC: Dan Williams <dan.j.williams@intel.com>
    > CC: Hannes Reinecke <hare@suse.com>

    Uh, I should have added this for my last comment on v1:
    Reviewed-by: John Garry <john.garry@huawei.com>

    > Reviewed-by: Hannes Reinecke <hare@suse.com>
    > ---
    > drivers/scsi/libsas/sas_expander.c | 9 ++++-----
    > 1 file changed, 4 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
    > index 52222940d398..0d1f72752ca2 100644
    > --- a/drivers/scsi/libsas/sas_expander.c
    > +++ b/drivers/scsi/libsas/sas_expander.c
    > @@ -48,17 +48,16 @@ static void smp_task_timedout(struct timer_list *t)
    > unsigned long flags;
    >
    > spin_lock_irqsave(&task->task_state_lock, flags);
    > - if (!(task->task_state_flags & SAS_TASK_STATE_DONE))
    > + if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
    > task->task_state_flags |= SAS_TASK_STATE_ABORTED;
    > + complete(&task->slow_task->completion);
    > + }
    > spin_unlock_irqrestore(&task->task_state_lock, flags);
    > -
    > - complete(&task->slow_task->completion);
    > }
    >
    > static void smp_task_done(struct sas_task *task)
    > {
    > - if (!del_timer(&task->slow_task->timer))
    > - return;
    > + del_timer(&task->slow_task->timer);
    > complete(&task->slow_task->completion);
    > }
    >
    >


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