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]
Message-Id: <1192751553.7367.57.camel@pasglop>
Date:	Fri, 19 Oct 2007 09:52:33 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	akpm@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] synchronize_irq needs a barrier


> So how about something like this (untested! not necessarily very well 
> thought through either!)
> 
> Basic notion: the only thing that serializes the IRQ_INPROGRESS flag is 
> the descriptor lock. And we don't have to (or even want to!) hold it while 
> waiting for the thing, but we want to *have*held*it* in between whatever 
> we're synchronizing with.
> 
> The internal irq handler functions already held the lock when they did 
> whatever they need to serialize - and they are possibly performance 
> critical too - so they use the "internal" function that doesn't get the 
> lock unnecessarily again.

That may do the trick as the read can't cross the spin_lock (it can
cross spin_unlock but not lock). Advantage over adding a barrier to
handle_IRQ_event() is that it keeps the overhead to the slow path
(synchronize_irq).

Note that I didn't actually experience a problem here. I just came upon
that by accident while thinking about a similar issue I have with
napi_synchronize().

Looks good to me on a first glance (unfortunately a bit ugly but heh).

Ben.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ