linux-kernel - Re: [PATCH -mm] slub: update cpu after new

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]

Date:	Wed, 25 Apr 2007 17:13:25 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Christoph Lameter <clameter@....com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] slub: update cpu after new_slab()

On Wed, 25 Apr 2007, Christoph Lameter wrote:
> On Wed, 25 Apr 2007, Hugh Dickins wrote:
> 
> > > Right. local_irq_save does not switch off preemption as I thought.
> > 
> > Strange comment.  Preemption is not possible while IRQs are disabled,
> > but new_slab() rightly reenables them within itself in the __GFP_WAIT
> > case, since it's going off to do a page allocation and may need to wait.
> 
> Yes I expected local_irq_save to increase the preempt count and then 
> local_irq_enable to simply enable interrupts without affecting the preempt 
> count. Thus the process should stay on the same processor.
> 
> Never thought it would be possible to move to a different processor in mid 
> flight.

But, surely you wouldn't have expected it to stay on the processor
throughout the waiting page allocation??  I think you're misremembering
your expectations, and this was just a simple, understandable, oversight.

Quite a serious one, though: it got caught in my case by the NULL
dereference, but it's probably been switching cpu there much more
often - one cpu diddling with what's private to another, with
unpredictable results.

Hugh
-
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/