linux-kernel - Re: [PATCH] mm: prevent RCU stalls in kswapd by adding cond

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: <aJeLGpT9vp7g0lj4@casper.infradead.org>
Date: Sat, 9 Aug 2025 18:53:30 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Subrata Nath (Nokia)" <subrata.nath@...ia.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: prevent RCU stalls in kswapd by adding cond_resched()

On Sat, Aug 09, 2025 at 10:38:45AM -0700, Andrew Morton wrote:
> On Sat, 9 Aug 2025 16:09:12 +0100 Matthew Wilcox <willy@...radead.org> wrote:
> 
> > On Sat, Aug 09, 2025 at 11:59:16AM +0000, Subrata Nath (Nokia) wrote:
> > > Fix this by adding cond_resched() after all spinlock release points
> > > in page_vma_mapped_walk() and in the main loop of shrink_zones().
> > > These calls, placed outside spinlock-held sections, allow voluntary
> > > scheduling and ensure timely quiescent state reporting, avoiding
> > > prolonged RCU stalls.
> > 
> > No.  We're removing cond_resched().  See
> > https://lore.kernel.org/linux-mm/87cyyfxd4k.ffs@tglx/
> > and many many other emails over the past few years.
> 
> tglx's email was sent two years ago.

... and there has been much progress since then.  Most recently,
https://lore.kernel.org/all/20250225035516.26443-1-boqun.feng@gmail.com/

This report is not from a recent kernel.  Subrata was good enough to
include:

Based on: v6.1.128

and I think it is very much on them to prove that this is still a
problem in 2025.