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

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Message-ID: <20241209141612.wtst3obur3xxbtiq@quack3>
Date: Mon, 9 Dec 2024 15:16:12 +0100
From: Jan Kara <jack@...e.cz>
To: Klara Modin <klarasmodin@...il.com>
Cc: Jan Kara <jack@...e.cz>, Josef Bacik <josef@...icpanda.com>,
	kernel-team@...com, linux-fsdevel@...r.kernel.org,
	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, sraithal@....com
Subject: Re: [PATCH v8 16/19] fsnotify: generate pre-content permission event
 on page fault

On Mon 09-12-24 13:56:47, Klara Modin wrote:
> Hi,
> 
> On 2024-12-09 13:31, Jan Kara wrote:
> > 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
> 
> My config was attached, but yes, I have

Ah, sorry, somehow I've missed that.

> CONFIG_FANOTIFY_ACCESS_PERMISSIONS=n. I tried the tip by Srikanth Aithal to
> enable it and that resolved the issue.
> 
> Your new for_next branch resolved the CONFIG_FANOTIFY_ACCESS_PERMISSIONS=n
> case for me.

Thanks for testing! Glad to hear the problem is solved.

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