[PATCH RT 03/10] hpsa: fix warning with smp_processor_id() in preemptible section

[Steven Rostedt]

From: John Kacur <jkacur@xxxxxxxxxx>

On a 3.6-rt (real-time patch) kernel we are seeing the following BUG
However, it appears to be relevant for non-realtime (mainline) as well.

|hpsa 0000:03:00.0: hpsa0: <0x323a> at IRQ 67 using DAC
|scsi0 : hpsa
|BUG: using smp_processor_id() in preemptible [0000000000000000] code: kworker/u:0/6
|caller is enqueue_cmd_and_start_io+0x5a/0x100 [hpsa]
|Pid: 6, comm: kworker/u:0 Not tainted 3.6.11.5-rt37.52.el6rt.x86_64.debug #1
|Call Trace:
| [<ffffffff812abe83>] debug_smp_processor_id+0x123/0x150
| [<ffffffffa009043a>] enqueue_cmd_and_start_io+0x5a/0x100 [hpsa]
| [<ffffffffa00905cb>] hpsa_scsi_do_simple_cmd_core+0xeb/0x110 [hpsa]
| [<ffffffff812b09c8>] ? swiotlb_dma_mapping_error+0x18/0x30
| [<ffffffff812b09c8>] ? swiotlb_dma_mapping_error+0x18/0x30
| [<ffffffffa0090701>] hpsa_scsi_do_simple_cmd_with_retry+0x91/0x280 [hpsa]
| [<ffffffffa0093558>] hpsa_scsi_do_report_luns.clone.2+0xd8/0x130 [hpsa]
| [<ffffffffa00935ea>] hpsa_gather_lun_info.clone.3+0x3a/0x1a0 [hpsa]
| [<ffffffffa00963df>] hpsa_update_scsi_devices+0x11f/0x4f0 [hpsa]
| [<ffffffff81592019>] ? sub_preempt_count+0xa9/0xe0
| [<ffffffffa00968ad>] hpsa_scan_start+0xfd/0x150 [hpsa]
| [<ffffffff8158cba8>] ? rt_spin_lock_slowunlock+0x78/0x90
| [<ffffffff813b04d7>] do_scsi_scan_host+0x37/0xa0
| [<ffffffff813b05da>] do_scan_async+0x1a/0x30
| [<ffffffff8107c4ab>] async_run_entry_fn+0x9b/0x1d0
| [<ffffffff8106ae92>] process_one_work+0x1f2/0x620
| [<ffffffff8106ae20>] ? process_one_work+0x180/0x620
| [<ffffffff8106d4fe>] ? worker_thread+0x5e/0x3a0
| [<ffffffff8107c410>] ? async_schedule+0x20/0x20
| [<ffffffff8106d5d3>] worker_thread+0x133/0x3a0
| [<ffffffff8106d4a0>] ? manage_workers+0x190/0x190
| [<ffffffff81073236>] kthread+0xa6/0xb0
| [<ffffffff815970a4>] kernel_thread_helper+0x4/0x10
| [<ffffffff81082a7c>] ? finish_task_switch+0x8c/0x110
| [<ffffffff8158e44b>] ? _raw_spin_unlock_irq+0x3b/0x70
| [<ffffffff8158e85d>] ? retint_restore_args+0xe/0xe
| [<ffffffff81073190>] ? kthreadd+0x1e0/0x1e0
| [<ffffffff815970a0>] ? gs_change+0xb/0xb

-------------------

This is caused by
enqueue_cmd_and_start_io()->
        set_performant_mode()->
                smp_processor_id()
Which if you have debugging enabled calls debug_processor_id() and triggers the warning.

The code here is
 c->Header.ReplyQueue = smp_processor_id() % h->nreply_queues;

Since it is not critical that the code complete on the same processor,
but the cpu is a hint used in generating the ReplyQueue and will still work if
the cpu migrates or is preempted, it is safe to use the raw_smp_processor_id()
to surpress the false positve warning.

Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: John Kacur <jkacur@xxxxxxxxxx>
Acked-by: Stephen <scameron@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 drivers/scsi/hpsa.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
index 4f33806..80a44b1 100644
--- a/drivers/scsi/hpsa.c
+++ b/drivers/scsi/hpsa.c
@@ -583,7 +583,7 @@ static void set_performant_mode(struct ctlr_info *h, struct CommandList *c)
 		c->busaddr |= 1 | (h->blockFetchTable[c->Header.SGList] << 1);
 		if (likely(h->msix_vector))
 			c->Header.ReplyQueue =
-				smp_processor_id() % h->nreply_queues;
+				raw_smp_processor_id() % h->nreply_queues;
 	}
 }
 
-- 
1.7.10.4


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