Re: riscv32 EXT4 splat, 6.8 regression?

From: Nam Cao <namcao@linutronix.de>
To: Andreas Dilger <adilger@dilger.ca>
Cc: "Mike Rapoport" <rppt@kernel.org>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Christian Brauner" <brauner@kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"Jan Kara" <jack@suse.cz>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-riscv@lists.infradead.org, "Theodore Ts'o" <tytso@mit.edu>,
	"Ext4 Developers List" <linux-ext4@vger.kernel.org>,
	"Conor Dooley" <conor@kernel.org>,
	"Anders Roxell" <anders.roxell@linaro.org>,
	"Alexandre Ghiti" <alex@ghiti.fr>
Subject: Re: riscv32 EXT4 splat, 6.8 regression?
Date: Thu, 18 Apr 2024 11:17:53 +0200	[thread overview]
Message-ID: <20240418111753.1c485974@namcao> (raw)
In-Reply-To: <1F07FFF3-663B-43D4-A9DA-C89856F2962A@dilger.ca>

On 2024-04-17 Andreas Dilger wrote:
> On Apr 16, 2024, at 4:36 PM, Nam Cao <namcao@linutronix.de> wrote:
> > However, I am confused about one thing: doesn't this make one page of
> > physical memory inaccessible?
> > 
> > Is it better to solve this by setting max_low_pfn instead? Then at
> > least the page is still accessible as high memory.  
> 
> Is that one page of memory really worthwhile to preserve?  Better to
> have a simple solution that works,

Good point.

> maybe even mapping that page
> read-only so that any code which tries to dereference an ERR_PTR
> address immediately gets a fault?

Not sure about this part: it doesn't really fix the problem, just
changes from subtle crashes into page faults.

Let me send a patch to reserve the page: simple and works for all
architectures.

Best regards,
Nam

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