Re: [syzbot] [fs?] possible deadlock in ovl_create_object (2)

From: "Jörn Engel" <joern@barelysecure.org>
To: Chris Roy <iam@thechris.in>
Cc: Richard Weinberger <richard@nod.at>,
	Greg KH <gregkh@linuxfoundation.org>,
	syzbot <syzbot+7cab6a19619f1b8efc00@syzkaller.appspotmail.com>,
	dakr@kernel.org, driver-core@lists.linux.dev,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	rafael@kernel.org, syzkaller-bugs@googlegroups.com,
	linux-mtd@lists.infradead.org, miquel.raynal@bootlin.com,
	vigneshr@ti.com, Adarsh Das <adarshdas950@gmail.com>
Subject: Re: [syzbot] [fs?] possible deadlock in ovl_create_object (2)
Date: Sat, 19 Sep 2026 08:38:31 -0700	[thread overview]
Message-ID: <aq6sd2Z3nZuAYbMG@cashel.logfs.org> (raw)
In-Reply-To: <CAE2Bdm3K+ZnrfB7xzkg=2fzMs7AmJzdF3aYCpN00h90TR6FMog@mail.gmail.com>

On Sat, Sep 19, 2026 at 08:58:51PM +0530, Chris Roy wrote:
> 
> I'd rather not bolt a redesign onto this fix.

Good decision!

> > Is this check necessary? [...] Looks like the kernel is still
> > undecided whether checks are necessary or not.
> 
> I will keep it. kzalloc()/kstrdup() under plain GFP_KERNEL can still
> return NULL under real memory pressure (no __GFP_NOFAIL here), and
> dropping it would be inconsistent with the kstrdup() check two lines
> below.

My foggy mind is slowly waking up.  GFP_ATOMIC can return NULL.  If
you're trying to allocate memory from an interrupt handler or similar,
you cannot afford to wait for memory reclaim to happen.  Those calls
definitely need a check and a reasonable plan what to do in case of
failure.

GFP_KERNEL should be able to block and wait, so there really is no
excuse for kmalloc to return NULL or for the callers to need a check.

But your decision of not pulling too many decisions into a single patch
is still a good decision.  Even if my logic is sound, removing checks
from kmalloc callers should be a separate effort.

Jörn

--
I don't understand it. Nobody does.
-- Richard P. Feynman

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