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  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]
Date:	Sat, 13 Dec 2014 16:14:58 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: frequent lockups in 3.18rc4

On Sat, Dec 13, 2014 at 3:47 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> static inline void mnt_dec_writers(struct mount *mnt)
> {
> #ifdef CONFIG_SMP
>         this_cpu_dec(mnt->mnt_pcp->mnt_writers);
> #else
>         mnt->mnt_writers--;
> #endif
> }
> It's load/modify/store, without any kind of atomicity; get preempted in the
> middle of that sequence by another caller of mnt_dec_writers() and obvious bad
> things will happen...

Ugh, yes ok, the UP case needs it for the actual counter itself. Ugh.
What an ugly mess. I'd rather have the preemption disable where it is
actually *needed*, in that function itself for the UP case (or just
make it "atomic_t", which would likely be better still.

                     Linus
--
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/

Powered by blists - more mailing lists