Re: [PATCH] net: use raw_cpu ops in snmp stats bh

[Sergey Senozhatsky]

Hello,

On Thu, Mar 6, 2014 at 9:13 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Date: Thu,  6 Mar 2014 15:55:36 +0300
>
>> Commit a25982c15ae52 ("percpu: add preemption checks to __this_cpu
>> ops") added preemption checks to __this_cpu ops, which are used in
>> SNMP_INC_STATS_BH() and SNMP_ADD_STATS_BH(), resulting in following
>> warnings:
>>
>> BUG: using __this_cpu_add() in preemptible [00000000] code: ssh/4661
>> caller is __this_cpu_preempt_check+0x2b/0x2d
>> CPU: 3 PID: 4661 Comm: ssh Not tainted 3.14.0-rc5-next-20140306-dbg-dirty #162
>> Hardware name: Acer             Aspire 5741G    /Aspire 5741G    , BIOS V1.20 02/08/2011
>>  0000000000000000 ffff880094939be0 ffffffff813b8305 0000000000000003
>>  ffff880094939c00 ffffffff8121221f ffff88015130a8c0 0000000000000000
>>  ffff880094939c38 ffffffff8121226b 635f736968745f5f 29286464615f7570
>> Call Trace:
>>  [<ffffffff813b8305>] dump_stack+0x4e/0x7a
>>  [<ffffffff8121221f>] check_preemption_disabled+0xce/0xdd
>>  [<ffffffff8121226b>] __this_cpu_preempt_check+0x2b/0x2d
>>  [<ffffffff81370b5a>] ? tcp_rearm_rto+0x9f/0xa1
>>  [<ffffffff81373456>] tcp_event_new_data_sent+0x6d/0x91
>>  [<ffffffff81374dc6>] tcp_write_xmit+0x3f1/0x935
>>  [<ffffffff813754e4>] __tcp_push_pending_frames+0x28/0x82
>>  [<ffffffff81368109>] tcp_push+0xcc/0x102
>>  [<ffffffff8136a0c1>] tcp_sendmsg+0x8c5/0xb7a
>>  [<ffffffff81207d59>] ? string.isra.6+0x3b/0x9f
>>  [<ffffffff8138a10a>] inet_sendmsg+0x75/0xa0
>>  [<ffffffff81320fb6>] sock_aio_write+0xe7/0xfe
>>  [<ffffffff81207d59>] ? string.isra.6+0x3b/0x9f
>>  [<ffffffff810e08ab>] do_sync_write+0x54/0x73
>>  [<ffffffff810e0df7>] vfs_write+0xc6/0x17c
>>  [<ffffffff810e1603>] SyS_write+0x44/0x78
>>  [<ffffffff813be0a1>] tracesys+0xd4/0xd9
>>
>> use raw_cpu_inc() and raw_cpu_add() instead of __this_cpu_inc()
>> and __this_cpu_add().
>>
>> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
>
> This is a bug in the TCP code, if this code path can happen outside of
> software interrupts or BH protected sections, which it can as seen in
> this trace, it must use the non-_BH-postfixed versions of the SNMP
> counter bumps.


David, Eric, thank you and sorry for the noise.


p.s. my fetchmail went mad two days ago and became very selective on
fetching mails from gmail, so I surely missed a lot of emails. have to double
check using web interface now.

-ss
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