linux-kernel - Re: [PATCH] Fix x86_64 _spin_lock

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: <44ED9CB4.7070302@FreeBSD.org>
Date:	Thu, 24 Aug 2006 14:33:56 +0200
From:	Suleiman Souhlal <ssouhlal@...eBSD.org>
To:	Andi Kleen <ak@...e.de>
CC:	Edward Falk <efalk@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix x86_64 _spin_lock_irqsave()

Andi Kleen wrote:
> On Thursday 24 August 2006 13:04, Suleiman Souhlal wrote:
> 
>>Andi Kleen wrote:
>>
>>>Edward Falk <efalk@...gle.com> writes:
>>>
>>>
>>>
>>>>Add spin_lock_string_flags and _raw_spin_lock_flags() to
>>>>asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same
>>>>semantics on x86_64 as it does on i386 and does *not* have interrupts
>>>>disabled while it is waiting for the lock.
>>>
>>>
>>>Did it fix anything for you?
>>
>>I think this was to work around the fact that some buggy drivers try to 
>>grab spinlocks without disabling interrupts when they should, which 
>>would cause deadlocks when trying to rendez-vous every cpu via IPIs.
> 
> 
> That doesn't help them at all because they could then deadlock later.

If the driver uses spin_lock() when it knows that the hardware won't 
generate the interrupt that would need to be masked, and 
spin_lock_irqsave() elsewhere, there shouldn't be any deadlocks unless 
IPIs are involved.

For example, say a driver uses spin_lock(&driver_lock) in its interrupt 
handler and spin_lock_irqsave(&driver_lock) elsewhere.
Imagine CPU1 is handling a such a interrupt while CPU2 is trying to send 
a packet (for example).

In a regular situation, CPU1 shouldn't be interrupted by anything 
needing driver_lock, and so it should be able to complete and let CPU2 
acquire the lock.

Now, if CPU3 is trying to do an IPI rendez-vous, it will interrupt CPU1 
and try to interrupt CPU2 too. However, since spin_lock_irqsave() spins 
with interrupts disabled, the system will deadlock.

With this patch, IPI rendez-vous shouldn't cause these problems, since 
it will let the rendez-vous will be able to complete. Or am I missing 
something?

-- Suleiman
-
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/