linux-kernel - Re: [PATCH 0/3] btrfs: Replace kmap() with kmap_local

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Message-ID: <20220602162840.GV20633@twin.jikos.cz>
Date:   Thu, 2 Jun 2022 18:28:40 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Ira Weiny <ira.weiny@...el.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] btrfs: Replace kmap() with kmap_local_page()

On Thu, Jun 02, 2022 at 08:20:08AM -0700, Christoph Hellwig wrote:
> Turns out that while this looks good, it actually crashes when
> running xfstests.  I think this is due to the fact that kmap sets
> the page address, which kmap_local_page does not.
> 
> btrfs/150 1s ... [  168.252943] run fstests btrfs/150 at 2022-06-02 15:17:11
> [  169.462292] BTRFS info (device vdb): flagging fs with big metadata feature
> [  169.463728] BTRFS info (device vdb): disk space caching is enabled
> [  169.464953] BTRFS info (device vdb): has skinny extents
> [  170.596218] BTRFS: device fsid 37c6bae1-d3e5-47f8-87d5-87cd7240a1b4
> devid 1 transid 5 /dev)
> [  170.599471] BTRFS: device fsid 37c6bae1-d3e5-47f8-87d5-87cd7240a1b4 devid 2 transid 5 /dev)
> [  170.657170] BTRFS info (device vdc): flagging fs with big metadata feature
> [  170.659509] BTRFS info (device vdc): use zlib compression, level 3
> [  170.661190] BTRFS info (device vdc): disk space caching is enabled
> [  170.670706] BTRFS info (device vdc): has skinny extents
> [  170.714181] BTRFS info (device vdc): checking UUID tree
> [  170.735058] BUG: kernel NULL pointer dereference, address: 0000000000000008
> [  170.736478] #PF: supervisor read access in kernel mode
> [  170.737457] #PF: error_code(0x0000) - not-present page
> [  170.738529] PGD 0 P4D 0 
> [  170.739211] Oops: 0000 [#1] PREEMPT SMP PTI
> [  170.740101] CPU: 0 PID: 43 Comm: kworker/u4:3 Not tainted 5.18.0-rc7+ #1539
> [  170.741478] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> [  170.743246] Workqueue: btrfs-delalloc btrfs_work_helper
> [  170.744282] RIP: 0010:zlib_compress_pages+0x128/0x670

I've just hit the crash too, so I've removed the patches from misc-next
until there's fixed version.