Change locking surrounding kmap_atomic from local_irqsave to 
local_irqsave_nort. This fixes issues with PREEMPT_RT.
 
Signed-off-by:  Jakub Jozwicki <jozwicki@aster.pl>

--- linux-2.6.25.10/drivers/ata/libata-core.c	2008-07-03 05:46:47.000000000 
+0200
+++ linux-2.6.25.10-rt7/drivers/ata/libata-core.c	2008-07-12 
23:59:33.132140258 +0200
@@ -5157,14 +5157,14 @@
 		unsigned long flags;
 
 		/* FIXME: use a bounce buffer */
-		local_irq_save(flags);
+		local_irq_save_nort(flags);
 		buf = kmap_atomic(page, KM_IRQ0);
 
 		/* do the actual data transfer */
 		ap->ops->data_xfer(qc->dev, buf + offset, qc->sect_size, do_write);
 
 		kunmap_atomic(buf, KM_IRQ0);
-		local_irq_restore(flags);
+		local_irq_restore_nort(flags);
 	} else {
 		buf = page_address(page);
 		ap->ops->data_xfer(qc->dev, buf + offset, qc->sect_size, do_write);
@@ -5294,14 +5294,14 @@
 		unsigned long flags;
 
 		/* FIXME: use bounce buffer */
-		local_irq_save(flags);
+		local_irq_save_nort(flags);
 		buf = kmap_atomic(page, KM_IRQ0);
 
 		/* do the actual data transfer */
 		consumed = ap->ops->data_xfer(dev,  buf + offset, count, rw);
 
 		kunmap_atomic(buf, KM_IRQ0);
-		local_irq_restore(flags);
+		local_irq_restore_nort(flags);
 	} else {
 		buf = page_address(page);
 		consumed = ap->ops->data_xfer(dev,  buf + offset, count, rw);
--

[ message continues ]

eww.  If we're going to have to do stuff like this in mainline then
there might be a revolt.

--

[ message continues ]

Sorry, this was for -rt only.

[   17.012011] BUG: sleeping function called from invalid context IRQ-14(5732) 
at arch/x86/mm/highmem_32.c:8
[   17.012011] in_atomic():0 [00000000], irqs_disabled():1
[   17.012011] Pid: 5732, comm: IRQ-14 Not tainted 2.6.25.10-rtXXX #11
[   17.012011]  [<c0120fc4>] __might_sleep+0xf1/0xf8
[   17.012011]  [<c011c035>] kmap+0x47/0x5a
[   17.012011]  [<c033e728>] ata_hsm_move+0x3d7/0x657
[   17.012011]  [<c0342fd6>] ata_interrupt+0x14e/0x1cb
[   17.012011]  [<c015c72c>] handle_IRQ_event+0x4e/0xd1
[   17.012011]  [<c015d266>] do_irqd+0x126/0x224
[   17.012011]  [<c015d140>] ? do_irqd+0x0/0x224
[   17.012011]  [<c013ae9d>] kthread+0x3b/0x62
[   17.012011]  [<c013ae62>] ? kthread+0x0/0x62
[   17.012011]  [<c0108287>] kernel_thread_helper+0x7/0x10
[   17.012011]  =======================

--

[ message continues ]

The subject says kmap_atomic, but this is kmap.  It definitely makes no 
sense to call kmap in an IRQ, regardless of the locking.  There seems to 

    J
--

[ message continues ]

--- linux-2.6.25.8-rt7.orig/include/asm-x86/highmem.h   2008-06-23 
19:12:47.000000000 -0400
+++ linux-2.6.25.8-rt7/include/asm-x86/highmem.h        2008-06-23 
19:13:58.000000000 -0400


+/*
+ * on PREEMPT_RT kmap_atomic() is a wrapper that uses kmap():
+ */
+#ifdef CONFIG_PREEMPT_RT
+# define kmap_atomic_prot(page, type, prot)    ({ pagefault_disable(); 
kmap(page); })
+# define kmap_atomic(page, type)       ({ pagefault_disable(); kmap(page); })
+# define kmap_atomic_pfn(pfn, type)    kmap(pfn_to_page(pfn))
+# define kunmap_atomic(kvaddr, type)   do { pagefault_enable(); 
kunmap_virt(kvaddr); } while(0)
+# define kmap_atomic_to_page(kvaddr)   kmap_to_page(kvaddr)
+#else
+# define kmap_atomic_prot(page, type, prot)    __kmap_atomic_prot(page, type, 
prot)
+# define kmap_atomic(page, type)       __kmap_atomic(page, type)
+# define kmap_atomic_pfn(pfn, type)    __kmap_atomic_pfn(pfn, type)
+# define kunmap_atomic(kvaddr, type)   __kunmap_atomic(kvaddr, type)
+# define kmap_atomic_to_page(kvaddr)   __kmap_atomic_to_page(kvaddr)
+#endif
+
--

[ message continues ]

OK, I guess the "structural problem" is RT ;)

    J
--

[ message continues ]

On Sun, 13 Jul 2008 01:27:36 +0200

The right way to fix this is to use a bounce buffer. I sent Jeff patches
to do that a couple of times. I'm not sure what has happened to them
since ? So NAK this, we should apply the patch to actually fix the bug
instead.

Jeff ?

Alan
--

[ message continues ]

Sent patch was for:

[   16.787021] BUG: sleeping function called from invalid context IRQ-14(5730) 
at arch/x86/mm/highmem_32.c:8
[   16.787021] in_atomic():0 [00000000], irqs_disabled():1
[   16.787021] Pid: 5730, comm: IRQ-14 Not tainted 2.6.25.10-rtXXX #12
[   16.787021]  [<c0120fc4>] __might_sleep+0xf1/0xf8
[   16.787021]  [<c011c035>] kmap+0x47/0x5a
[   16.787021]  [<c03442b2>] ata_scsi_rbuf_get+0x23/0x31
[   16.787021]  [<c0345975>] atapi_qc_complete+0x252/0x2c5
[   16.787021]  [<c012edee>] ? irq_exit+0x7b/0x7e
[   16.787021]  [<c0109727>] ? do_IRQ+0x6e/0x87
[   16.787021]  [<c033d041>] __ata_qc_complete+0x8e/0x93
[   16.787021]  [<c033ddfb>] ata_qc_complete+0x182/0x188
[   16.787021]  [<c033e188>] ata_hsm_qc_complete+0xa1/0xa5
[   16.787021]  [<c033e8fd>] ata_hsm_move+0x5dd/0x628
[   16.787021]  [<c0342f76>] ata_interrupt+0x14e/0x1cb
[   16.787021]  [<c015c72c>] handle_IRQ_event+0x4e/0xd1
[   16.787021]  [<c015d266>] do_irqd+0x126/0x224
[   16.787021]  [<c015d140>] ? do_irqd+0x0/0x224
[   16.787021]  [<c013ae9d>] kthread+0x3b/0x62
[   16.787021]  [<c013ae62>] ? kthread+0x0/0x62
[   16.787021]  [<c0108287>] kernel_thread_helper+0x7/0x10
[   16.787021]  =======================

--

[ message continues ]

Fine - but the right fix is still to apply the patches that use a bounce
buffer, otherwise you might paper over the warning but you'll trash rt
performance. It needs fixing anyway especially with Tejun's changes to
the ATAPI logic to use PIO more often

Alan
--

[ message continues ]