Re: [6.4-current oops] null ptr deref in blk_mq_sched_bio_merge() from blkdev readahead

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On Wed, May 3, 2023 at 2:06 PM Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> Hi folks,
>
> fstests running shared/032 on XFS with a default mkfs and mount
> config causes a panic in the block layer when userspace is operating
> directly on the block device like this:
>
> SECTION       -- xfs
> FSTYP         -- xfs (debug)
> PLATFORM      -- Linux/x86_64 test3 6.3.0-dgc+ #1792 SMP PREEMPT_DYNAMIC Wed May  3 15:20:20 AEST 2023
> MKFS_OPTIONS  -- -f -m rmapbt=1 /dev/pmem1
> MOUNT_OPTIONS -- -o dax=never -o context=system_u:object_r:root_t:s0 /dev/pmem1 /mnt/scratch
>
> ....
>
> [   56.070695] run fstests shared/032 at 2023-05-03 15:21:55
> [   56.768890] BTRFS: device fsid 355df15c-7bc5-49b0-9b5d-dc25ce855a9d devid 1 transid 6 /dev/pmem1 scanned by mkfs.btrfs (5836)
> [   57.285879]  pmem1: p1
> [   57.301845] BUG: kernel NULL pointer dereference, address: 00000000000000a8
> [   57.304562] #PF: supervisor read access in kernel mode
> [   57.306499] #PF: error_code(0x0000) - not-present page
> [   57.308414] PGD 0 P4D 0
> [   57.309401] Oops: 0000 [#1] PREEMPT SMP
> [   57.310876] CPU: 3 PID: 4478 Comm: (udev-worker) Not tainted 6.3.0-dgc+ #1792
> [   57.313517] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [   57.317089] RIP: 0010:blk_mq_sched_bio_merge+0x7b/0x100

Hi Dave,

It is fixed by:

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-6.4/block&id=38c8e3dfb2a1be863b7f5aad7755d5e9727da8a5

Thanks,
Ming





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