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

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Message-ID: <20240414020457.GI187181@mit.edu>
Date: Sat, 13 Apr 2024 22:04:57 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Andreas Dilger <adilger@...ger.ca>
Cc: Nam Cao <namcao@...utronix.de>,
        Björn Töpel <bjorn@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv@...ts.infradead.org,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Conor Dooley <conor@...nel.org>
Subject: Re: riscv32 EXT4 splat, 6.8 regression?

On Sat, Apr 13, 2024 at 07:46:03PM -0600, Andreas Dilger wrote:
> This looks like a straight-forward mathematical substitution of "dlimit"
> with "search_buf + buf_size" and rearranging of the terms to make the
> while loop offset "zero based" rather than "address based" and would
> avoid overflow if "search_buf" was within one 4kB block of overflow:
> 
>    dlimit = search_buf + buf_size = 0xfffff000 + 0x1000 = 0x00000000

Umm... maybe, but does riscv32 actually have a memory map where a
kernel page would actually have an address in high memory like that?
That seems.... unusual.

If we have a reliable reproduction, can someone actually printk the
address or test to see if this theory is correct?

	   	       	       - Ted