linux-kernel - Re: I2C from interrupt context?

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] [day] [month] [year] [list]

Date:	Mon, 10 Nov 2008 23:57:34 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Krzysztof Halasa <khc@...waw.pl>
Cc:	Jean Delvare <khali@...ux-fr.org>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: I2C from interrupt context?

On Fri, 07 Nov 2008 17:05:35 +0100 Krzysztof Halasa <khc@...waw.pl> wrote:

> Jean Delvare <khali@...ux-fr.org> writes:
> 
> > The situation is far from perfect though. For one thing, I seem to
> > recall that Andrew Morton didn't like the approach taken in
> > i2c_transfer(). For another, i2c_smbus_xfer() was not yet modified so
> > at this point only I2C-level transactions can be non-sleeping,
> > SMBus-level transactions can't. But all this could be fixed by anyone
> > who cares about these specific issues.
> 
> Thanks, I'll look at it.

The problem (well: bug) is that in_atomic() returns false inside a
spinlock when CONFIG_PREEMPT=n.  The code as it stands can sleep
inside a spinlock, which is deadlockable if a scheduled-to task
tries to take the same spinlock.

There is no means like this by which a piece of code can determine
whether it can call schedule().  The pattern which we use in many many
places (most especially GFP_KERNEL/GFP_ATOMIC) is to pass a flag down
to callees telling them in some manner which context they were called from.
--
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/