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From: "Theodore Ts'o" <tytso@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Mackall <mpm@selenic.com>,
	Linux Kernel Developers List <linux-kernel@vger.kernel.org>,
	w@1wt.eu, ewust@umich.edu, zakir@umich.edu, greg@kroah.com,
	nadiah@cs.ucsd.edu, jhalderm@umich.edu, tglx@linutronix.de,
	davem@davemloft.net, stable@kernel.org
Subject: Re: [PATCH 01/10] random: make 'add_interrupt_randomness()' do something sane
Date: Thu, 5 Jul 2012 18:00:40 -0400	[thread overview]
Message-ID: <20120705220040.GA15685@thunk.org> (raw)
In-Reply-To: <CA+55aFxAe1pRN+jvdLveHQ+nNRNC6HDZ+S4Y9P202rxgNLN8pg@mail.gmail.com>

On Thu, Jul 05, 2012 at 02:47:52PM -0700, Linus Torvalds wrote:
> On Thu, Jul 5, 2012 at 2:39 PM, Matt Mackall <mpm@selenic.com> wrote:
> >
> > From my read, this code path gets called on timer interrupts too.
> 
> That's hopefully never true for any normal cases (timers are *very*
> special - they tend to go through their own architecture-specific
> stuff). On modern PC's, for example, the timers happen through the
> local apic timers directly.
> 
> In fact, with SMP, it's a really bad idea to use a normal irq for
> timer interrupts, since you really really want per-CPU-core timers.
> 
> But yes, we should probably make sure that *if* the architecture uses
> regular interrupts for timers we don't count them. The problematic
> embedded platforms are often pretty crap hardware: even when they are
> SMP, they might use an external timer irq (and then we broadcast the
> thing). I think we have the IRQF_TIMER flag for that, so we could add
> a check for that.

Like this?

						- Ted

diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 8270db0..0ce4863 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -133,7 +133,7 @@ irqreturn_t
 handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 {
 	irqreturn_t retval = IRQ_NONE;
-	unsigned int random = 0, irq = desc->irq_data.irq;
+	unsigned int random = 1, irq = desc->irq_data.irq;
 
 	do {
 		irqreturn_t res;
@@ -161,7 +161,8 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 
 			/* Fall through to add to randomness */
 		case IRQ_HANDLED:
-			random |= action->flags;
+			if (action->flags & __IRQF_TIMER)
+				random = 0;
 			break;
 
 		default:
@@ -172,7 +173,8 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
 		action = action->next;
 	} while (action);
 
-	add_interrupt_randomness(irq);
+	if (random)
+		add_interrupt_randomness(irq);
 
 	if (!noirqdebug)
 		note_interrupt(irq, desc, retval);

  reply	other threads:[~2012-07-05 22:01 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-05 18:12 [PATCH 00/10] /dev/random fixups Theodore Ts'o
2012-07-05 18:12 ` [PATCH 01/10] random: make 'add_interrupt_randomness()' do something sane Theodore Ts'o
2012-07-05 18:47   ` Matt Mackall
2012-07-05 18:52     ` Linus Torvalds
2012-07-05 21:39       ` Matt Mackall
2012-07-05 21:47         ` Linus Torvalds
2012-07-05 22:00           ` Theodore Ts'o [this message]
2012-07-05 22:21             ` Linus Torvalds
2012-07-05 22:31               ` Matt Mackall
2012-07-05 22:35                 ` Linus Torvalds
2012-07-05 23:21                 ` Theodore Ts'o
2012-07-06  2:59                   ` Linus Torvalds
2012-07-06 13:01                     ` Theodore Ts'o
2012-07-06 16:24                       ` Linus Torvalds
2012-07-06 16:52                         ` Theodore Ts'o
2012-07-09 19:15                           ` Matt Mackall
2012-07-25 18:43                         ` Thomas Gleixner
     [not found]   ` <CAGsuqq2MWuFnY7PMb_2ddBNNJr80xB_JW+Wryq3mhhmQuEojpg@mail.gmail.com>
2012-07-06 21:59     ` Theodore Ts'o
2012-07-05 18:12 ` [PATCH 02/10] random: use lockless techniques when mixing entropy pools Theodore Ts'o
2012-07-05 18:18   ` Linus Torvalds
2012-07-05 18:19   ` Greg KH
2012-07-05 23:09     ` Theodore Ts'o
2012-07-05 19:10   ` Matt Mackall
2012-07-05 19:47     ` Theodore Ts'o
2012-07-05 20:45       ` Matt Mackall
2012-07-05 18:12 ` [PATCH 03/10] random: create add_device_randomness() interface Theodore Ts'o
2012-07-05 18:12 ` [PATCH 04/10] usb: feed USB device information to the /dev/random driver Theodore Ts'o
2012-07-05 18:12 ` [PATCH 05/10] net: feed /dev/random with the MAC address when registering a device Theodore Ts'o
2012-07-05 18:12 ` [PATCH 06/10] random: use the arch-specific rng in xfer_secondary_pool Theodore Ts'o
2012-07-05 18:49   ` Linus Torvalds
2012-07-05 18:12 ` [PATCH 07/10] random: add new get_random_bytes_arch() function Theodore Ts'o
2012-07-05 18:35   ` Linus Torvalds
2012-07-05 19:50     ` Theodore Ts'o
2012-07-05 21:45     ` Matt Mackall
2012-07-25  3:37   ` H. Peter Anvin
2012-07-25  7:22     ` Ingo Molnar
2012-07-25 15:10     ` Theodore Ts'o
2012-07-25 15:19       ` H. Peter Anvin
2012-07-25 17:37       ` [PATCH] random: mix in architectural randomness in extract_buf() H. Peter Anvin
2012-07-25 23:50         ` Ben Hutchings
2012-07-26  0:32           ` H. Peter Anvin
2012-07-28  2:39         ` Theodore Ts'o
2012-07-28  2:48           ` H. Peter Anvin
2012-07-26  3:16       ` [PATCH 07/10] random: add new get_random_bytes_arch() function H. Peter Anvin
2012-07-26  3:24         ` H. Peter Anvin
2012-07-05 18:12 ` [PATCH 08/10] random: unify mix_pool_bytes() and mix_pool_bytes_entropy() Theodore Ts'o
2012-07-05 18:12 ` [PATCH 09/10] random: add tracepoints for easier debugging and verification Theodore Ts'o
2012-07-05 18:12 ` [PATCH 10/10] MAINTAINERS: Theodore Ts'o is taking over the random driver Theodore Ts'o
2012-07-06 11:40 ` [PATCH 00/10] /dev/random fixups Fengguang Wu
2012-07-06 12:44   ` Theodore Ts'o
2012-07-20 20:15 ` [PATCH] dmi: Feed DMI table to /dev/random driver Tony Luck
2012-07-20 21:03   ` Matt Mackall
2012-07-21  0:56   ` Theodore Ts'o
2012-07-21  1:19     ` Tony Luck
2012-07-21  2:02       ` Theodore Ts'o
2012-07-23 16:47         ` [PATCH] random: Add comment to random_initialize() Tony Luck

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