[BUG] bug when enabling VM DEBUG

[saeed bishara]

Jeff,
seems that the libata do pio to buffer which was allocated with
kmalloc, and under arm arch, the flush_dcache_page() is needed to
prevent cache aliasing, the later function calls the page_mapping
which falls on PageSlab(page)

as the flush_dcache_page() is needed to prevent aliasing, it can be
skipped if the page is Slab as such pages are used only by the kernel.
here a suggested patch:

--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -894,7 +894,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
                                       do_write);
        }

-       if (!do_write)
+       if (!do_write && !PageSlab(page))
                flush_dcache_page(page);

saeed


On Mon, May 10, 2010 at 4:06 PM, saeed bishara <saeed.bishara at gmail.com> wrote:
> Hi,
>  I got the following bug when enabling the VM_DEBGU on 2.6.34-rc6:
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000000
> pgd = c0004000
> [00000000] *pgd=00000000
> Internal error: Oops: 805 [#1]
> last sysfs file:
> Modules linked in:
> CPU: 0    Not tainted  (2.6.34-rc6-00176-g00047b8-dirty #331)
> PC is at flush_dcache_page+0x2c/0xc4
> LR is at ata_pio_sector+0xd8/0x124
> pc : [<c002d30c>]    lr : [<c01c29d4>]    psr: 20000013
> sp : f5513ee8  ip : 79a50000  fp : 00001ee8
> r10: 00000058  r9 : f54f0000  r8 : 00000000
> r7 : f54f1358  r6 : c03e6b84  r5 : 00000000  r4 : 00000000
> r3 : 00000000  r2 : 00000000  r1 : f54f17b8  r0 : c0ac4e20
> Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> Control: 10c5387d  Table: 00004019  DAC: 00000017
> Process ata/0 (pid: 145, stack limit = 0xf55122f0)
> Stack: (0xf5513ee8 to 0xf5514000)
> 3ee0:                   c0ac4e20 c01c29d4 00000009 f54f1358 f54f1358 00000001
> 3f00: c040d18c c01c2ad8 00000005 00000009 f54f0000 c01c3204 c03cfe78 00000000
> 3f20: 00200200 f54f13d4 c00446e4 00000001 f54f1424 00000000 00000000 00000000
> 3f40: 00000000 00000000 ffffffff 00000009 f54f0000 f54f1358 00000001 c040d18c
> 3f60: 00000005 0000000a 00001ee8 c01c46d8 f5413c70 f54b5b68 c01c45d4 f54b5b60
> 3f80: f5512000 f5513f9c 00000000 00000000 00000000 c004b2c0 00000000 00000000
> 3fa0: f54be0c0 c004e12c f5513fa8 f5513fa8 f5429ec8 f5513fd4 f5429ec8 f54b5b60
> 3fc0: c004b1c8 00000000 00000000 c004e014 00000000 00000000 f5513fd8 f5513fd8
> 3fe0: 00000000 00000000 00000000 00000000 00000000 c0026dec bc7e4afb 6a3a8a30
> [<c002d30c>] (flush_dcache_page+0x2c/0xc4) from [<c01c29d4>]
> (ata_pio_sector+0xd8/0x124)
> [<c01c29d4>] (ata_pio_sector+0xd8/0x124) from [<c01c2ad8>]
> (ata_pio_sectors+0xb8/0xc4)
> [<c01c2ad8>] (ata_pio_sectors+0xb8/0xc4) from [<c01c3204>]
> (ata_sff_hsm_move+0x618/0x76c)
> [<c01c3204>] (ata_sff_hsm_move+0x618/0x76c) from [<c01c46d8>]
> (ata_pio_task+0x104/0x124)
> [<c01c46d8>] (ata_pio_task+0x104/0x124) from [<c004b2c0>]
> (worker_thread+0xf8/0x170)
> [<c004b2c0>] (worker_thread+0xf8/0x170) from [<c004e014>] (kthread+0x78/0x80)
> [<c004e014>] (kthread+0x78/0x80) from [<c0026dec>] (kernel_thread_exit+0x0/0x8)
> Code: e5904010 e3130080 0a000002 e3a03000 (e5833000)
> ---[ end trace 8a7ce1ae66250005 ]---
>