From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ajay Kaher <akaher@vmware.com>, Al Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>
Subject: Re: [for-next][PATCH 2/3] eventfs: Stop using dcache_readdir() for getdents()
Date: Thu, 4 Jan 2024 15:33:04 -0500 [thread overview]
Message-ID: <20240104153304.79e607c8@gandalf.local.home> (raw)
In-Reply-To: <CAHk-=wik=OOYCRSzAA7x485GyxH97ioaPziiF4Ms1kRU8VLkHA@mail.gmail.com>
On Thu, 4 Jan 2024 12:18:06 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Thu, 4 Jan 2024 at 12:04, Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > Also, I just realized it breaks if we update the 'c--' before the callback. :-/
> >
> > I have to put this check *after* the callback check.
>
> What? No.
>
> > Reason being, the callback can say "this event doesn't get this file" and
> > return 0, which tells eventfs to skip this file.
>
> So yes, there seems to be a bug there, in that ctx->pos is only
> updated for successful callbacks (and not for "ignored entry").
OK, I wasn't sure if it was OK to update the ctx->pos for something we
didn't add, so I avoided doing so.
>
> But that just means that you should always update 'ctx->pos' as you
> 'continue' the loop.
>
> The logical place to do that would be in the for-loop itself, which
> actually is very natural for the simple case, ie you should just do
>
> for (i = 0; i < ei->nr_entries; i++, ctx->pos++) {
Well, we don't want to do that and c-- at the same time. But of course, if
we do the shortcut, we can have:
for (i = c; i < ei->nr_entries; i++, ctx->pos++) {
which would be OK. And better if we move it before the ei->children list walk.
>
> but in the list_for_each_entry_srcu() case the 'update' part of the
> for-loop isn't actually accessible, so it would have to be at the
> 'continue' point(s).
>
> Which is admittedly a bit annoying.
But not really an issue as we just have:
list_for_each_entry_srcu(ei_child, &ei->children, list,
srcu_read_lock_held(&eventfs_srcu)) {
if (c > 0) {
c--;
continue;
}
ctx->pos++;
>
> Looking at that I'm actually surprised that I don't recall that we'd
> have hit that issue with our 'for_each_xyz()' loops before.
>
> The update for our "for_each_xyz()" helpers are all hardcoded to just
> do the "next iterator" thing, and there's no nice way to take
> advantage of the normal for-loop semantics of "do this at the end of
> the loop"
Anyway, if I do count ctx->pos++ for every iteration, whether it added
something or not, it appears to work. I'll write up a couple of patches to
handle this.
Thanks,
-- Steve
next prev parent reply other threads:[~2024-01-04 20:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-04 16:47 [for-next][PATCH 0/3] tracefs/eventfs: Updates for 6.8 Steven Rostedt
2024-01-04 16:47 ` [for-next][PATCH 1/3] eventfs: Remove "lookup" parameter from create_dir/file_dentry() Steven Rostedt
2024-01-04 16:47 ` [for-next][PATCH 2/3] eventfs: Stop using dcache_readdir() for getdents() Steven Rostedt
2024-01-04 18:46 ` Linus Torvalds
2024-01-04 19:02 ` Steven Rostedt
2024-01-04 20:05 ` Steven Rostedt
2024-01-04 20:18 ` Linus Torvalds
2024-01-04 20:33 ` Steven Rostedt [this message]
2024-01-15 20:58 ` Steven Rostedt
2024-01-04 16:47 ` [for-next][PATCH 3/3] tracefs/eventfs: Use root and instance inodes as default ownership Steven Rostedt
2024-01-04 18:38 ` Linus Torvalds
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