linux-kernel - Re: [PATCH PREEMPT_RT]: On AT91 ARM: GPIO Interrupt handling can/will stall forever

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 for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <3efb10970711280638l3f57104y8cf9f2e58235c3@mail.gmail.com>
Date:	Wed, 28 Nov 2007 15:38:11 +0100
From:	"Remy Bohmer" <linux@...mer.net>
To:	"Daniel Walker" <dwalker@...sta.com>
Cc:	"Steven Rostedt" <rostedt@...dmis.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...e.hu>,
	"ARM Linux Mailing List" <linux-arm-kernel@...ts.arm.linux.org.uk>,
	RT <linux-rt-users@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH PREEMPT_RT]: On AT91 ARM: GPIO Interrupt handling can/will stall forever

Hello Daniel,

>  *      Note: The caller is expected to handle the ack, clear, mask and
>  *      unmask issues if necessary.
> So we shouldn't need any flow control unless there is some other
> factors..

This comment can be misinterpreted, I think. Who is assumed to be the
caller in this context? The 2 other routines in the driver that
actually do the unmasking stuff besides only calling this routine? Is
it allowed to call it directly or should it always be done through a
wrapper that does all these special things?

Either way, only masking interrupts, and never unmasking it, is a bug.
If interrupts come and go slow enough you never run into this problem,
and if this type is not used often, nobody will notice it.
Usually interrupts needs clearence of the source before the hardware
can generate a new one. GPIO interrupts are different, they are
generated whenever a IO-level changes, there is no acknowledge or
clearing of the interupt needed. These types of interrupts are never
'pending' from hardware point of view. So, with these type of
interrupts, a new one can occur while the interrupt handler has not
handled the previous one yet, and therefor these interrupt-types will
show this bug.

>
> Additionally, we have a patch in the real time tree called
> "irq-mask-fix.patch" which adds an "unmask" to handle_simple_irq, but as
> the note says we don't need flow control..

You mean the Montavista real time tree?

Kind Regards,

Remy
-
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/