linux-kernel - Re: [PATCH] eventfs: Stop using dcache

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Date: Wed, 3 Jan 2024 14:06:45 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>, 
	Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Al Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] eventfs: Stop using dcache_readdir() for getdents()

On Wed, 3 Jan 2024 at 13:54, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Here's an updated patch that builds, and is PURELY AN EXAMPLE.

Oh, and while doing this patch, I found another bug in tracefs,
although it happily is one that doesn't have any way to trigger.

Tracefs has code like this:

        if (dentry->d_inode->i_mode & S_IFDIR) {

and that's very wrong. S_IFDIR is not a bitmask, it's a value that is
part of S_IFMT.

The reason this bug doesn't have any way to trigger is that I think
tracefs can only have S_IFMT values of S_IFDIR and S_IFREG, and those
happen to not have any bits in common, so doing it as a bit test is
wrong, but happens to work.

The test *should* be done as

        if (S_ISDIR(dentry->d_inode->i_mode)) {

(note "IS" vs "IF" - not the greatest user experience ever, but hey,
it harkens back to Ye Olden Times).

                Linus