linux-kernel - Re: [PATCH v3 fanotify 1/2] fanotify: Introduce fanotify filter

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Message-ID: <20241128163705.vuvmb5k6ryyiblt5@quack3>
Date: Thu, 28 Nov 2024 17:37:05 +0100
From: Jan Kara <jack@...e.cz>
To: Amir Goldstein <amir73il@...il.com>
Cc: Song Liu <song@...nel.org>, bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, kernel-team@...a.com,
	andrii@...nel.org, eddyz87@...il.com, ast@...nel.org,
	daniel@...earbox.net, martin.lau@...ux.dev, viro@...iv.linux.org.uk,
	brauner@...nel.org, jack@...e.cz, kpsingh@...nel.org,
	mattbobrowski@...gle.com, repnop@...gle.com, jlayton@...nel.org,
	josef@...icpanda.com, mic@...ikod.net, gnoack@...gle.com
Subject: Re: [PATCH v3 fanotify 1/2] fanotify: Introduce fanotify filter

On Sun 24-11-24 07:25:20, Amir Goldstein wrote:
> On Sat, Nov 23, 2024 at 12:00 AM Song Liu <song@...nel.org> wrote:
...
> > @@ -921,6 +924,39 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
> >         pr_debug("%s: group=%p mask=%x report_mask=%x\n", __func__,
> >                  group, mask, match_mask);
> >
> > +       if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS))
> > +               fsid = fanotify_get_fsid(iter_info);
> > +
> > +#ifdef CONFIG_FANOTIFY_FILTER
> > +       filter_hook = srcu_dereference(group->fanotify_data.filter_hook, &fsnotify_mark_srcu);
> 
> Do we actually need the sleeping rcu protection for calling the hook?
> Can regular rcu read side be nested inside srcu read side?

Nesting rcu inside srcu is fine.

> Jan,
> 
> I don't remember why srcu is needed since we are not holding it
> when waiting for userspace anymore?

You need srcu to access marks or notification group unless you grab a
reference to them (which is what waiting for permission event reply code
does).
 
								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR