linux-kernel - Re: [PATCH v2] fs/buffer: add alert in try_to_free

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Message-ID: <aUAWwPWDq0GgAjnP@casper.infradead.org>
Date: Mon, 15 Dec 2025 14:10:08 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Christian Brauner <brauner@...nel.org>
Cc: jack@...e.cz, Deepakkumar Karn <dkarn@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH v2] fs/buffer: add alert in try_to_free_buffers() for
 folios without buffers

On Mon, Dec 15, 2025 at 03:07:35PM +0100, Christian Brauner wrote:
> On Thu, 11 Dec 2025 18:42:11 +0530, Deepakkumar Karn wrote:
> > try_to_free_buffers() can be called on folios with no buffers attached
> > when filemap_release_folio() is invoked on a folio belonging to a mapping
> > with AS_RELEASE_ALWAYS set but no release_folio operation defined.
> > 
> > In such cases, folio_needs_release() returns true because of the
> > AS_RELEASE_ALWAYS flag, but the folio has no private buffer data. This
> > causes try_to_free_buffers() to call drop_buffers() on a folio with no
> > buffers, leading to a null pointer dereference.
> > 
> > [...]
> 
> Applied to the vfs-7.0.misc branch of the vfs/vfs.git tree.
> Patches in the vfs-7.0.misc branch should appear in linux-next soon.

No, this is the wrong fix.  Please drop.