Re: Scheduling while atomic

[Mike Christie]

On 01/07/2011 01:37 AM, Max Matveev wrote:

I'm working with a customer who's getting the famous "scheduling while
atomic" noise in the logs when using his tape library connected via
iSCSI. The task is always an iscsi_q_31 and they're getting a lot of
those BUG messages.

I have the backtrace but it's almost useless - the code path is
unbelievable: the only reliable bit is

  [<f8acca0e>] iscsi_tcp_segment_done+0x1c7/0x2a7 [libiscsi_tcp]
  [<c05b7f45>] kernel_sendmsg+0x27/0x35
  [<f8ad33e8>] iscsi_sw_tcp_pdu_xmit+0x9e/0x1e8 [iscsi_tcp]
  [<f8acc246>] iscsi_tcp_task_xmit+0x25/0x204 [libiscsi_tcp]
  [<f8d9b622>] iscsi_xmit_task+0x24/0x4b [libiscsi2]
  [<f8d9c190>] iscsi_xmitworker+0x122/0x202 [libiscsi2]

If other people are hitting this try the attached patch.

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diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c
index 8eeb39f..e98ae33 100644
--- a/drivers/scsi/libiscsi_tcp.c
+++ b/drivers/scsi/libiscsi_tcp.c
@@ -132,14 +132,25 @@ static void iscsi_tcp_segment_map(struct iscsi_segment 
*segment, int recv)
        if (page_count(sg_page(sg)) >= 1 && !recv)
                return;
 
-       segment->sg_mapped = kmap_atomic(sg_page(sg), KM_SOFTIRQ0);
+       if (recv) {
+               segment->atomic_mapped = true;
+               segment->sg_mapped = kmap_atomic(sg_page(sg), KM_SOFTIRQ0);
+       } else {
+               segment->atomic_mapped = false;
+               /* the xmit path can sleep with the page mapped so use kmap */
+               segment->sg_mapped = kmap(sg_page(sg));
+       }
+
        segment->data = segment->sg_mapped + sg->offset + segment->sg_offset;
 }
 
 void iscsi_tcp_segment_unmap(struct iscsi_segment *segment)
 {
        if (segment->sg_mapped) {
-               kunmap_atomic(segment->sg_mapped, KM_SOFTIRQ0);
+               if (segment->atomic_mapped)
+                       kunmap_atomic(segment->sg_mapped, KM_SOFTIRQ0);
+               else
+                       kunmap(sg_page(segment->sg));
                segment->sg_mapped = NULL;
                segment->data = NULL;
        }
diff --git a/include/scsi/libiscsi_tcp.h b/include/scsi/libiscsi_tcp.h
index 741ae7e..e6b9fd2 100644
--- a/include/scsi/libiscsi_tcp.h
+++ b/include/scsi/libiscsi_tcp.h
@@ -47,6 +47,7 @@ struct iscsi_segment {
        struct scatterlist      *sg;
        void                    *sg_mapped;
        unsigned int            sg_offset;
+       bool                    atomic_mapped;
 
        iscsi_segment_done_fn_t *done;
 };