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Date: Wed, 19 Feb 2014 11:46:49 -0800 From: Eric Dumazet <eric.dumazet@...il.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: Florian Westphal <fw@...len.de>, David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [PATCH -next] net: tcp: add mib counters to track zero window transitions On Wed, 2014-02-19 at 20:30 +0100, Hannes Frederic Sowa wrote: > NET_STATS only use 32 bit counter and thus need not be protected with a > seqlock on 32 bit platforms. As such, it does not matter, but e.g. the IP > counter are prone to deadlocks if used with wrong postfix because of 64 bit > counter thus protected by seqlock. > > A pitty that the _STATS_BH postfixes have the opposite meaning of the bottom > _bh postfixes. > > Basically always safe is _STATS and if we are sure we can omit the bh disable > call because we only call the function from bh, we can use _STATS_BH calls. Using __this_cpu_inc() is not safe in preemptable contexts. Sure, x86 doesn't care, but other arches might. Fortunately LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES can be incremented only for a retransmit, and they should always happen from BH. Better avoid the confusion for this ultra rare case, I'll send a patch. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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