linux-kernel - Re: How is jiffies upation while holding spinlock in Uniprocessor or SMP environment?

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:	Mon, 26 Oct 2015 10:48:54 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	raghu MG <raghumag@...il.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Andrew Lunn <andrew@...n.ch>
Subject: Re: How is jiffies upation while holding spinlock in Uniprocessor or
 SMP environment?

On Mon, Oct 26, 2015 at 12:19:31PM +0530, raghu MG wrote:
> Hello,
> I have couple of questions.
> 1) In case of UP how is jiffies(timer) get updated while holding spin
> lock using spinlock_irq_save?

It isn't, and...
> 
> 2)My understanding is in smp environment jiffies updation cannot be
> done on processor holding spinlock irrespective of spinlock API.So
> timer interrupt should be enabled across all cores in SoC. Imagine a
> scenario in quad core processor where 4 cores are holding 4 different
> spinlocks & how is the timer interrupt for jiffies handled?

You can't rely on jiffies being updated while holding a spinlock.
Expecting jiffies to update while holding a spinlock is a bug.

-- 
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
--
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/