netdev - Re: question about softirqs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 13 May 2009 09:05:01 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Miller <davem@...emloft.net>, linuxppc-dev@...abs.org,
	paulus@...ba.org, netdev@...r.kernel.org
Subject: Re: question about softirqs

Andi Kleen wrote:
> Thomas Gleixner <tglx@...utronix.de> writes:

>>Err, no. Chris is completely correct:
>>
>>        if (!in_interrupt())
>>		wakeup_softirqd();
> 
> Yes you have to wake it up just in case, but it doesn't normally
> process the data because a normal softirq comes in faster. It's
> just a safety policy. 

What about the scenario I raised earlier, where we have incoming network
packets, no hardware interrupts coming in other than the timer tick, and
a high-priority userspace app is spinning on recvmsg() with MSG_DONTWAIT
set?

As far as I can tell, in this scenario softirqs may not get processed on
return from a syscall (contradicting the documentation).  In the worst
case, they may not get processed until the next timer tick.

Chris
--
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