linux-ext4 - Re: riscv32 EXT4 splat, 6.8 regression?

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Date: Thu, 18 Apr 2024 11:17:53 +0200
From: Nam Cao <namcao@...utronix.de>
To: Andreas Dilger <adilger@...ger.ca>
Cc: Mike Rapoport <rppt@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 Björn Töpel <bjorn@...nel.org>, Christian Brauner
 <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel
 <linux-fsdevel@...r.kernel.org>, Jan Kara <jack@...e.cz>, Linux Kernel
 Mailing List <linux-kernel@...r.kernel.org>,
 linux-riscv@...ts.infradead.org, Theodore Ts'o <tytso@....edu>, Ext4
 Developers List <linux-ext4@...r.kernel.org>, Conor Dooley
 <conor@...nel.org>, Anders Roxell <anders.roxell@...aro.org>, Alexandre
 Ghiti <alex@...ti.fr>
Subject: Re: riscv32 EXT4 splat, 6.8 regression?

On 2024-04-17 Andreas Dilger wrote:
> On Apr 16, 2024, at 4:36 PM, Nam Cao <namcao@...utronix.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