From: "David S. Miller" <davem@redhat.com>
To: Krishna Kumar <kumarkr@us.ibm.com>
Cc: kuznet@ms2.inr.ac.ru, mashirle@us.ibm.com, netdev@oss.sgi.com,
xma@us.ibm.com
Subject: Re: [PATCH]snmp6 64-bit counter support in proc.c
Date: Wed, 28 Jan 2004 11:09:45 -0800 [thread overview]
Message-ID: <20040128110945.662a4d6a.davem@redhat.com> (raw)
In-Reply-To: <OF27A95A54.FAB6CE99-ON88256E24.000E2136@us.ibm.com>
On Thu, 22 Jan 2004 18:45:18 -0800
Krishna Kumar <kumarkr@us.ibm.com> wrote:
> / * Overflow, sync and re-read, the next read is guaranteed to
> be greater
> * than res1.
> */
> synchronize_kernel();
> res2 = *((__u64 *) (((void *) per_cpu_ptr(mib[0], i)) + sizeof
> (__u64) * nr)));
I don't understand how your scheme can work.
We're trying to detect if the upper 32-bit half of the 64-bit value
belongs with the lower-half. We can overflow the lower-half TWICE
in the res1=...res2=... sequence you do, and this res2 reread in the if
branch can overflow itself again, combining a lower and upper half which
do not belong to each other.
This is not so trivial to fix, see? :)
next prev parent reply other threads:[~2004-01-28 19:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-01-23 2:45 [PATCH]snmp6 64-bit counter support in proc.c Krishna Kumar
2004-01-28 19:09 ` David S. Miller [this message]
-- strict thread matches above, loose matches on Subject: below --
2004-01-28 20:15 Shirley Ma
2004-01-28 20:09 Shirley Ma
2004-01-28 19:19 Krishna Kumar
2004-01-28 19:33 ` David S. Miller
2004-01-23 18:06 Shirley Ma
2004-01-23 2:57 Krishna Kumar
2004-01-23 1:08 Shirley Ma
2004-01-23 1:43 ` David S. Miller
2004-01-22 22:50 Krishna Kumar
2004-01-23 0:35 ` David S. Miller
2004-01-22 21:18 Krishna Kumar
2004-01-22 22:10 ` David S. Miller
2004-01-21 23:44 Shirley Ma
2004-01-21 19:45 Shirley Ma
2004-01-21 20:27 ` YOSHIFUJI Hideaki / 吉藤英明
2004-01-21 22:05 ` David S. Miller
2004-01-22 18:26 ` kuznet
2003-12-05 21:55 Shirley Ma
2003-12-02 12:40 IPv6 MIB:ipv6PrefixTable implementation kuznet
2003-12-05 20:14 ` [PATCH]snmp6 64-bit counter support in proc.c Shirley Ma
2003-12-05 20:31 ` David S. Miller
2004-01-14 22:52 ` Shirley Ma
2004-01-15 8:57 ` David S. Miller
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