linux-kernel - Re: Serious problem with ticket spinlocks on ia64

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]

Message-Id: <201008302341.14312.ptesarik@suse.cz>
Date:	Mon, 30 Aug 2010 23:41:13 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Hedi Berriche <hedi@....com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Serious problem with ticket spinlocks on ia64

On Monday 30 of August 2010 20:17:25 Luck, Tony wrote:
> > I may tinker with this test a bit to include some short random
> > amounts of hold-time for the lock, and delays between attempts
> > to acquire it (to make it look more like a contended kernel lock
> > and less like a continuous queue of processes trading around a
> > lock that is never free
>
> I've been iterating ... adding new bits to try to reproduce the
> kernel environment:

Hi Tony,

I've been also playing with my test case, and I haven't been able to reproduce 
it in user-space either. One thing I noticed was the apparently incorrect use 
of ALAT. The generated code for _spin_lock_irq contains:

invala;;
ld4.c.nc r11=[r32]
// Other instructions not affecting r20
ld4.c.nc r20=[r32]

IIUC, the subsequent compare can use an undefined value (r20 is not modified 
anywhere in this function, except by the ld4.c.nc, but that happens only on 
an ALAT miss, right?).

I changed the corresponding code in __ticket_spin_lock to:

   asm volatile ("ld4.c.nc %0=[%1]" : "+r"(serve) : "r"(p) : "memory");

(NB the "+r" constraint instead of "=r")

The generated code now re-uses r15. Unfortunately, Hedi's test case still 
fails for me. :(

Petr Tesarik
--
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/