Re: [PATCH v2] BNX2I: Fixed kernel panic due to illegal usage of sc->request->cpu

["Michael Chan" <mchan@broadcom.com>]

On Thu, 2011-07-14 at 16:42 -0700, Eddie Wai wrote:
> A kernel panic was observed when passing the sc->request->cpu = -1 to
> retrieve the per_cpu variable pointer:
>  #0 [ffff880011203960] machine_kexec at ffffffff81022bc3
>  #1 [ffff8800112039b0] crash_kexec at ffffffff81088630
>  #2 [ffff880011203a80] __die at ffffffff8139ea20
>  #3 [ffff880011203aa0] no_context at ffffffff8102f3a7
>  #4 [ffff880011203ae0] __bad_area_nosemaphore at ffffffff8102f665
>  #5 [ffff880011203ba0] retint_signal at ffffffff8139dd1f
>  #6 [ffff880011203cc8] bnx2i_indicate_kcqe at ffffffffa03dc4f2
>  #7 [ffff880011203da8] service_kcqes at ffffffffa03cb04f
>  #8 [ffff880011203e68] cnic_service_bnx2x_kcq at ffffffffa03cb14a
>  #9 [ffff880011203e88] cnic_service_bnx2x_bh at ffffffffa03cb1b3
> 
> The problem lies in the sg_io (and perhaps sg_scsi_ioctl) call to
> blk_get_request->get_request/wait->blk_alloc_request->blk_rq_init which
> re-initializes the request->cpu to -1.  There is no assignment for cpu from
> that to the request_fn call to low level drivers.
> 
> When this happens, the sc->request->cpu will be using the init value of
> -1.  This will create a kernel panic when it hits bnx2i because the code
> refers it to get the per_cpu variables ptr.
> 
> This change is to put in a guard against that and also for cases when
> bio affinity/queue completion to the same cpu is not enabled.  In those
> cases, the request->cpu will remain a -1 also.
> 
> This bug was created from commit:  b5cf6b63f73abdc051035f0050b367beeb2ef94c
> 
> For the case when the blk layer did not setup the request->cpu, bnx2i
> will complete the sc with the current CPU of the thread.
> 
> Signed-off-by: Eddie Wai <eddie.wai@broadcom.com>
> ---
>  drivers/scsi/bnx2i/bnx2i_hwi.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/bnx2i/bnx2i_hwi.c b/drivers/scsi/bnx2i/bnx2i_hwi.c
> index 54978c1..0e71615 100644
> --- a/drivers/scsi/bnx2i/bnx2i_hwi.c
> +++ b/drivers/scsi/bnx2i/bnx2i_hwi.c
> @@ -1901,6 +1901,7 @@ static int bnx2i_queue_scsi_cmd_resp(struct iscsi_session *session,
>  	struct iscsi_task *task;
>  	struct scsi_cmnd *sc;
>  	int rc = 0;
> +	int cpu;
>  
>  	spin_lock(&session->lock);
>  	task = iscsi_itt_to_task(bnx2i_conn->cls_conn->dd_data,
> @@ -1912,7 +1913,13 @@ static int bnx2i_queue_scsi_cmd_resp(struct iscsi_session *session,
>  	sc = task->sc;
>  	spin_unlock(&session->lock);
>  
> -	p = &per_cpu(bnx2i_percpu, sc->request->cpu);
> +	if (!blk_rq_cpu_valid(sc->request)) {
> +		cpu = get_cpu();
> +		put_cpu();

Why not just use smp_processor_id()?

> +	} else
> +		cpu = sc->request->cpu;
> +
> +	p = &per_cpu(bnx2i_percpu, cpu);
>  	spin_lock(&p->p_work_lock);
>  	if (unlikely(!p->iothread)) {
>  		rc = -EINVAL;