We are inside spin_lock_irqsave().  quoth akpm's debug facility:
 [  231.948000] SCSI device sda: 
195371568 512-byte hdwr sectors (100030 MB)
 [  232.232000] ata1.00: configured for UDMA/33
 [  232.404000] WARNING (1) at arch/i386/mm/highmem.c:47 kmap_atomic()
 [  232.404000]  [<
c01162e6>] kmap_atomic+0xa9/0x1ab
 [  232.404000]  [<
c0242c81>] ata_scsi_rbuf_get+0x1c/0x30
 [  232.404000]  [<
c0242caf>] ata_scsi_rbuf_fill+0x1a/0x87
 [  232.404000]  [<
c0243ab2>] ata_scsiop_mode_sense+0x0/0x309
 [  232.404000]  [<
c01729d5>] end_bio_bh_io_sync+0x0/0x37
 [  232.404000]  [<
c02311c6>] scsi_done+0x0/0x16
 [  232.404000]  [<
c02311c6>] scsi_done+0x0/0x16
 [  232.404000]  [<
c0242dcc>] ata_scsi_simulate+0xb0/0x13f
[...]
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
                struct scatterlist *sg;
 
                sg = (struct scatterlist *) cmd->request_buffer;
-               buf = kmap_atomic(sg->page, KM_USER0) + sg->offset;
+               buf = kmap_atomic(sg->page, KM_IRQ0) + sg->offset;
                buflen = sg->length;
        } else {
                buf = cmd->request_buffer;
                struct scatterlist *sg;
 
                sg = (struct scatterlist *) cmd->request_buffer;
-               kunmap_atomic(buf - sg->offset, KM_USER0);
+               kunmap_atomic(buf - sg->offset, KM_IRQ0);
        }
 }