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Tony Lindgren bc417e30f8 net: Add back alignment for size for __alloc_skb 
Commit 87fb4b7b53 (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

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 		2011-11-03 18:09:16 -04:00
..
Makefile
…
datagram.c net: add skb frag size accessors 2011-10-19 03:10:46 -04:00
dev.c vlan: allow nested vlan_do_receive() 2011-10-30 04:43:30 -04:00
dev_addr_lists.c
…
drop_monitor.c
…
dst.c
…
ethtool.c
…
fib_rules.c Merge branch 'master' of ra.kernel.org:/pub/scm/linux/kernel/git/davem/net 2011-10-24 18:18:09 -04:00
filter.c filter: use unsigned int to silence static checker warning 2011-10-19 19:35:51 -04:00
flow.c net/flow: Fix potential memory leak 2011-10-17 19:18:42 -04:00
gen_estimator.c
…
gen_stats.c
…
iovec.c
…
kmap_skb.h
…
link_watch.c
…
neighbour.c neigh: Kill bogus SMP protected debugging message. 2011-11-01 17:45:55 -04:00
net-sysfs.c
…
net-sysfs.h
…
net-traces.c
…
net_namespace.c
…
netevent.c
…
netpoll.c
…
pktgen.c pktgen: remove ndelay() call 2011-10-20 17:00:21 -04:00
request_sock.c
…
rtnetlink.c if_link: Add additional parameter to IFLA_VF_INFO for spoof checking 2011-10-16 13:15:38 -07:00
scm.c af_unix: dont send SCM_CREDENTIALS by default 2011-09-28 13:29:50 -04:00
secure_seq.c tcp: add const qualifiers where possible 2011-10-21 05:22:42 -04:00
skbuff.c net: Add back alignment for size for __alloc_skb 2011-11-03 18:09:16 -04:00
sock.c net: Unlock sock before calling sk_free() 2011-10-25 19:17:25 -04:00
stream.c
…
sysctl_net_core.c
…
timestamping.c net: hold sock reference while processing tx timestamps 2011-10-24 02:54:50 -04:00
user_dma.c net: add skb frag size accessors 2011-10-19 03:10:46 -04:00
utils.c
…