linux-kernel - Re: [GIT, RFC] Killing the Big Kernel Lock

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Message-Id: <201003242259.58535.arnd@arndb.de>
Date:	Wed, 24 Mar 2010 22:59:57 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Matthew Wilcox <matthew@....cx>,
	Thomas Gleixner <tglx@...utronix.de>, jblunck@...e.de,
	Alan Cox <alan@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [GIT, RFC] Killing the Big Kernel Lock

On Wednesday 24 March 2010 22:53:07 Roland Dreier wrote:
> Interesting work.  For the drivers/infiniband part, it seems maybe all
> these drivers should be using no_llseek instead of default_llseek?  (or
> is it better style to use nonseekable_open()?)  Certainly as far as I
> can tell, nothing in drivers/infiniband pays any attention to f_pos.

no_llseek makes it clear that you don't want the default_llseek semantics,
while nonseekable_open also prevents pread/pwrite. Ideally, I'd just
use both.

There is a small chance that a random user space application actually tries
to seek on the device (e.g. SEEK_END) and expects a zero return value,
so when in doubt, I converted everything to default_llseek instead of
no_llseek, just so I can be sure I don't change the semantics.

> Also, is there a reason why you add "#include <linux/smp_lock.h>" to all
> the files where you also do ".llseek  = default_llseek"?

The last patch in the series moves the default_llseek and default_ioctl
function into the same loadable module that contains the BKL itself.
Moving the declarations into the respective header seemed appropriate,
but it could also stay in a VFS header if people prefer that.

> In any case I can at least take care of the llseek stuff for 2.6.35.

Ok, thanks!

	Arnd
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