Re: Linux 6.9.y btrfs: "NULL pointer dereference in attach_eb_folio_to_filemap" and "BUG: soft lockup" issues

[David Sterba <dsterba@suse.cz>]

Hi,

On Mon, Jun 17, 2024 at 01:33:59PM +0200, Jaroslav Pulchart wrote:
> Hello,
> 
> We recently upgraded part of our production environment to kernel
> 6.9.y. Since then, we've been encountering random kernel "NULL pointer
> dereference" and "soft lockup" errors when using BTRFS. These issues
> occur sporadically, sometimes after several days, and I haven't been
> able to reproduce them consistently. Due to this unpredictability,
> bisecting is not a feasible option.
> 
> Attached are console logs from some instances of these issues:
> * "NULL pointer dereference" in "btrfs.issue.1.log"
> * "soft lockup" in "btrfs.issue.1.log"
> Any assistance with investigating and resolving these problems would
> be greatly appreciated.

thanks for the report, the symptoms match the problem that was fixed
recently by commit f3a5367c679d ("btrfs: protect folio::private when
attaching extent buffer folios").

> [1072053.328255] CPU: 15 PID: 2354438 Comm: kworker/u195:18 Tainted: G            E      6.9.3-1.gdc.el9.x86_64 #1

6.9.3 does not have the fix yet (unless you're using a manually patched
kernel), it's in 6.9.5.