lkml.org 
[lkml]   [2011]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] net: Add back alignment for size for __alloc_skb
* Eric Dumazet <eric.dumazet@gmail.com> [111102 15:56]:
> On 03/11/2011 00:24, Tony Lindgren wrote:
>
>
> >
> > Seems to be SLOB for omap1_defconfig.
> >
> > Tony
>
>
> OK this makes sense now
>
> Your patch is absolutely needed, I completely forgot about SLOB :(
>
> since, kmalloc(386) on SLOB gives exactly ksize=386 bytes, not nearest
> power of two.
>
> [ 60.305763] malloc(size=385)->ffff880112c11e38 ksize=386 -> nsize=2
> [ 60.305921] malloc(size=385)->ffff88007c92ce28 ksize=386 -> nsize=2
> [ 60.306898] malloc(size=656)->ffff88007c44ad28 ksize=656 -> nsize=272
> [ 60.325385] malloc(size=656)->ffff88007c575868 ksize=656 -> nsize=272
> [ 60.325531] malloc(size=656)->ffff88011c777230 ksize=656 -> nsize=272
> [ 60.325701] malloc(size=656)->ffff880114011008 ksize=656 -> nsize=272
> [ 60.346716] malloc(size=385)->ffff880114142008 ksize=386 -> nsize=2
> [ 60.346900] malloc(size=385)->ffff88011c777690 ksize=386 -> nsize=2
>
> Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
>
> Thanks !

OK, thanks for explaining why it happens :) I also verified this does
not happen with SLAB or SLUB, only with SLOB.

I've updated the patch withyour comments and ack, updated patch below.

Regards,

Tony


From: Tony Lindgren <tony@atomide.com>
Date: Wed, 2 Nov 2011 15:46:41 -0700
Subject: [PATCH] net: Add back alignment for size for __alloc_skb

Commit 87fb4b7b533073eeeaed0b6bf7c2328995f6c075 (net: more
accurate skb truesize) changed the alignment of size. This
can cause problems at least on some machines with NFS root:

Unhandled fault: alignment exception (0x801) at 0xc183a43a
Internal error: : 801 [#1] PREEMPT
Modules linked in:
CPU: 0 Not tainted (3.1.0-08784-g5eeee4a #733)
pc : [<c02fbba0>] lr : [<c02fbb9c>] psr: 60000013
sp : c180fef8 ip : 00000000 fp : c181f580
r10: 00000000 r9 : c044b28c r8 : 00000001
r7 : c183a3a0 r6 : c1835be0 r5 : c183a412 r4 : 000001f2
r3 : 00000000 r2 : 00000000 r1 : ffffffe6 r0 : c183a43a
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
Control: 0005317f Table: 10004000 DAC: 00000017
Process swapper (pid: 1, stack limit = 0xc180e270)
Stack: (0xc180fef8 to 0xc1810000)
fee0: 00000024 00000000
ff00: 00000000 c183b9c0 c183b8e0 c044b28c c0507ccc c019dfc4 c180ff2c c0503cf8
ff20: c180ff4c c180ff4c 00000000 c1835420 c182c740 c18349c0 c05233c0 00000000
ff40: 00000000 c00e6bb8 c180e000 00000000 c04dd82c c0507e7c c050cc18 c183b9c0
ff60: c05233c0 00000000 00000000 c01f34f4 c0430d70 c019d364 c04dd898 c04dd898
ff80: c04dd82c c0507e7c c180e000 00000000 c04c584c c01f4918 c04dd898 c04dd82c
ffa0: c04ddd28 c180e000 00000000 c0008758 c181fa60 3231d82c 00000037 00000000
ffc0: 00000000 c04dd898 c04dd82c c04ddd28 00000013 00000000 00000000 00000000
ffe0: 00000000 c04b2224 00000000 c04b21a0 c001056c c001056c 00000000 00000000
Function entered at [<c02fbba0>] from [<c019dfc4>]
Function entered at [<c019dfc4>] from [<c01f34f4>]
Function entered at [<c01f34f4>] from [<c01f4918>]
Function entered at [<c01f4918>] from [<c0008758>]
Function entered at [<c0008758>] from [<c04b2224>]
Function entered at [<c04b2224>] from [<c001056c>]
Code: e1a00005 e3a01028 ebfa7cb0 e35a0000 (e5858028)

Here PC is at __alloc_skb and &shinfo->dataref is unaligned because
skb->end can be unaligned without this patch.

As explained by Eric Dumazet <eric.dumazet@gmail.com>, this happens
only with SLOB, and not with SLAB or SLUB:

* Eric Dumazet <eric.dumazet@gmail.com> [111102 15:56]:
>
> Your patch is absolutely needed, I completely forgot about SLOB :(
>
> since, kmalloc(386) on SLOB gives exactly ksize=386 bytes, not nearest
> power of two.
>
> [ 60.305763] malloc(size=385)->ffff880112c11e38 ksize=386 -> nsize=2
> [ 60.305921] malloc(size=385)->ffff88007c92ce28 ksize=386 -> nsize=2
> [ 60.306898] malloc(size=656)->ffff88007c44ad28 ksize=656 -> nsize=272
> [ 60.325385] malloc(size=656)->ffff88007c575868 ksize=656 -> nsize=272
> [ 60.325531] malloc(size=656)->ffff88011c777230 ksize=656 -> nsize=272
> [ 60.325701] malloc(size=656)->ffff880114011008 ksize=656 -> nsize=272
> [ 60.346716] malloc(size=385)->ffff880114142008 ksize=386 -> nsize=2
> [ 60.346900] malloc(size=385)->ffff88011c777690 ksize=386 -> nsize=2

Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -189,6 +189,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
* aligned memory blocks, unless SLUB/SLAB debug is enabled.
* Both skb->head and skb_shared_info are cache line aligned.
*/
+ size = SKB_DATA_ALIGN(size);
size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
data = kmalloc_node_track_caller(size, gfp_mask, node);
if (!data)

\
 
 \ /
  Last update: 2011-11-03 00:43    [W:0.039 / U:0.012 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site