linux-ext4 - Re: [PATCH v8 16/19] fsnotify: generate pre-content permission event on page fault

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Message-ID: <20241209123405.n7rwqtblqgy5p3bw@quack3>
Date: Mon, 9 Dec 2024 13:34:05 +0100
From: Jan Kara <jack@...e.cz>
To: "Aithal, Srikanth" <sraithal@....com>
Cc: Klara Modin <klarasmodin@...il.com>, Josef Bacik <josef@...icpanda.com>,
	kernel-team@...com, linux-fsdevel@...r.kernel.org, jack@...e.cz,
	amir73il@...il.com, brauner@...nel.org,
	torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
	linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-mm@...ck.org, linux-ext4@...r.kernel.org,
	Linux-Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH v8 16/19] fsnotify: generate pre-content permission event
 on page fault

On Mon 09-12-24 16:15:32, Aithal, Srikanth wrote:
> On 12/8/2024 10:28 PM, Klara Modin wrote:
> > Hi,
> > 
> > On 2024-11-15 16:30, Josef Bacik wrote:
> > > FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending
> > > on the faulting method.
> > > 
> > > This pre-content event is meant to be used by hierarchical storage
> > > managers that want to fill in the file content on first read access.
> > > 
> > > Export a simple helper that file systems that have their own ->fault()
> > > will use, and have a more complicated helper to be do fancy things with
> > > in filemap_fault.
> > > 
> > 
> > This patch (0790303ec869d0fd658a548551972b51ced7390c in next-20241206)
> > interacts poorly with some programs which hang and are stuck at 100 %
> > sys cpu usage (examples of programs are logrotate and atop with root
> > privileges).
> > 
> > I also retested the new version on Jan Kara's for_next branch and it
> > behaves the same way.
> 
> From linux-next20241206 onward we started hitting issues where KVM guests
> running kernel > next20241206 on AMD platforms fails to shutdown, hangs
> forever with below errors:

Thanks for report! This was discussed in [1] and I've just pushed out a
branch which has this bug fixed.

[1] https://lore.kernel.org/all/20241208152520.3559-1-spasswolf@web.de

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR