Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections

[Suzanne Wood]

With the spotlight leaving in_dev_get, we have the parallel question 
of in_dev_put() and __in_dev_put()  both defined with refcnt 
decrement, but the preceding underscore may lend itself to an
inadvertant pairing and refcnt inaccuracy.

In the following  cscope of linux-2.6.14-rc2 prior to Herbert's patches 
which remove the occurence in pktgen.c and the others are
paired with __in_dev_get_rtnl(), except xfrm4_policy.c():

C symbol: __in_dev_put
  File           Function              Line
  File           Function              Line
0 inetdevice.h   <global>               172 #define __in_dev_put(idev) atomic_dec(&(idev)->refcnt)
1 pktgen.c       pktgen_setup_inject   1687 __in_dev_put(in_dev);
2 devinet.c      inet_rtm_deladdr       412 __in_dev_put(in_dev);
3 igmp.c         igmp_gq_timer_expire   686 __in_dev_put(in_dev);
4 igmp.c         igmp_ifc_timer_expire  698 __in_dev_put(in_dev);
5 igmp.c         igmp_heard_query       801 __in_dev_put(in_dev);
6 igmp.c         ip_mc_down            1228 __in_dev_put(in_dev);
7 igmp.c         ip_mc_down            1231 __in_dev_put(in_dev);
8 igmp.c         ip_mc_find_dev        1310 __in_dev_put(idev);
9 xfrm4_policy.c xfrm4_dst_ifdown       280 __in_dev_put(loopback_idev);

It may not be reasonable to rename __in_dev_put for its parallel definition
since its current usage is with __in_dev_get_rtnl() which does not increment 
refcnt. 

It is also probably good to retain the old __in_dev_get() 
and __in_dev_put() and deprecate them.

Old business:  this is probably stating the obvious,
with Herbert's patches in place, none of the test patch
I'd submitted 8 Sept should take effect.

Thank you.
Suzanne

----- Original Message ----- 
From: "Herbert Xu" <herbert@xxxxxxxxxxxxxxxxxxx>
Sent: Saturday, October 01, 2005 12:12 AM

> On Fri, Sep 30, 2005 at 11:56:41PM -0700, Suzanne Wood wrote:
>> 
>> The other thing I'd hoped to address in pktgen.c was 
>> removing the __in_dev_put() which decrements refcnt 
>> while __in_dev_get_rcu() does not increment.
> 
> Well spotted.
> 
> Here is a patch on top of the last one to fix this bogus decrement.
> 
> Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

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