linux-ext4 - Re: [PATCH] ext4: remove unnecessary checks for __GFP

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Message-ID: <CAHB1NaigAoV3kUowQFnj3CBmPLcQMpHWMuL_pFOtKQd_An4A+A@mail.gmail.com>
Date: Sat, 1 Mar 2025 22:32:50 +0800
From: Julian Sun <sunjunchao2870@...il.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: Baokun Li <libaokun1@...wei.com>, linux-ext4@...r.kernel.org, 
	adilger.kernel@...ger.ca, jack@...e.cz, Yang Erkun <yangerkun@...wei.com>
Subject: Re: [PATCH] ext4: remove unnecessary checks for __GFP_NOFAIL allocation.

Hi, Ted.

On Fri, Feb 28, 2025 at 9:34 PM Theodore Ts'o <tytso@....edu> wrote:
>
> On Fri, Feb 28, 2025 at 05:30:06PM +0800, Julian Sun wrote:
> > > Actually, even with __GFP_NOFAIL set, kcalloc() can still return NULL,
> > > such as when the input parameters overflow.
> > >
> > Yeah, agreed. But IMO an overflow shouldn’t happen in this situation.
> >
> > If there's something I'm missing, please let me know.
>
> It's not a matter of missing something; or even Right vs Wrong.
> Different maintainers have different tastes about this sort of thing.
>
> The mm folks have changed the meaning of __GFP_NOFAIL in the past
> (TL;DR: they *hate* that concept, and I wouldn't be surprised if they
> try to change its behavior in the future) and especially in large code
> bases such as the Linux Kernel, I'm a big believer in defensive
> programming.
>
> As Linus has said in a different thread, when a compiler adds warnings
> because of what it thinks are "unnecessary" range checks, that's a bad
> warning.  Adding extra range checks is never a bad thing, and compiler
> behaviour that whine about that sort of thing are.... unfortunate.
> Similarly, I'd much rather keep the extra check.
>
> (Also, there exist static program checkers, such as Coverity, that
> don't know about the semantics of the GFP_* flags, and so removing the
> check would actually cause those tools to complain.)
>
Got it. Thanks for your detailed explanation, it makes sense to me.
By the way, I know you're busy, and I’m not trying to rush you, but
when you have some time, could you please take a look at these
patches? Thank you!

https://lore.kernel.org/linux-ext4/20250107044702.1836852-1-sunjunchao2870@gmail.com/

> Cheers,
>
>                                         - Ted


Best Regards,
-- 
Julian Sun <sunjunchao2870@...il.com>