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

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Message-ID: <20241209123137.o6bzwr35kumi2ksv@quack3>
Date: Mon, 9 Dec 2024 13:31:37 +0100
From: Jan Kara <jack@...e.cz>
To: Klara Modin <klarasmodin@...il.com>
Cc: 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
Subject: Re: [PATCH v8 16/19] fsnotify: generate pre-content permission event
 on page fault

Hello!

On Sun 08-12-24 17:58:42, Klara Modin wrote:
> 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.

Thanks for report! What is your kernel config please? I've just fixed a
bug reported by [1] which manifested in the same way with
CONFIG_FANOTIFY_ACCESS_PERMISSIONS=n.

Can you perhaps test with my for_next branch I've just pushed out? Thanks!

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