From: Matthew Wilcox <willy@infradead.org>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>,
adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
linux-kernel@vger.kernel.org, joneslee@google.com,
linux-mm@kvack.org
Subject: Re: [PATCH] ext4: remove superfluous check that pointer is not NULL
Date: Mon, 8 May 2023 22:13:27 +0100 [thread overview]
Message-ID: <ZFll93wsEUZIV/aI@casper.infradead.org> (raw)
In-Reply-To: <ZFkf/oJnCLZSWgYr@mit.edu>
On Mon, May 08, 2023 at 12:14:54PM -0400, Theodore Ts'o wrote:
> On Mon, May 08, 2023 at 03:13:37PM +0000, Tudor Ambarus wrote:
> > If @buffer is NULL, no operation is performed for kvfree(buffer),
> > remove superfluous check.
> >
> > Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
>
> I was looking at this just a few weeks ago, and I couldn't find any
> actual *documentation* that it was safe to call vfree(NIILL) or
> kvfree(NULL). The problem is there are a lot of architecture-specific
> functions, and unlike with kfree() there is no top-level "if (ptr ==
> NULL) return;" in the top-level vfree() and kvfree().
There doesn't need to be in kvfree(). is_vmalloc_addr() returns 'false'
for NULL, so it calls kfree(), which as you note has an explicit check
for ZERO_OR_NULL_PTR(). is_vmalloc_addr() also returns false for the
ZERO pointer, fwiw.
I agree that this should be explicitly documented as allowed, since it's
not reasonable to expect users to dig through these functions to verify
that such a change is safe.
next prev parent reply other threads:[~2023-05-08 21:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-08 15:13 [PATCH] ext4: remove superfluous check that pointer is not NULL Tudor Ambarus
2023-05-08 16:14 ` Theodore Ts'o
2023-05-08 21:13 ` Matthew Wilcox [this message]
2023-05-09 18:53 ` Theodore Ts'o
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