Re: [PATCH] hpsa: fix boot on ia64 (atomic_t alignment)

John Paul Adrian Glaubitz
2021-03-24T07:08:17Z

Hello!

On 3/12/21 11:27 PM, Sergei Trofimovich wrote:
> The failure initially observed as boot failure on rx3600 ia64 machine
> with RAID bus controller: Hewlett-Packard Company Smart Array P600:
>
> kernel unaligned access to 0xe000000105dd8b95, ip=0xa000000100b87551
> kernel unaligned access to 0xe000000105dd8e95, ip=0xa000000100b87551
> hpsa 0000:14:01.0: Controller reports max supported commands of 0 Using 16 instead. Ensure that firmware is up to date.
> swapper/0[1]: error during unaligned kernel access
>
> Here unaligned access comes from 'struct CommandList' that happens
> to be packed. The change f749d8b7a ("scsi: hpsa: Correct dev cmds
> outstanding for retried cmds") introduced unexpected padding and
> un-aligned atomic_t from natural alignment to something else.
>
> This change does not remove packing annotation from struct but only
> restores alignment of atomic variable.
>
> The change is tested on the same rx3600 machine.
>
> CC: linux-ia64@vger.kernel.org
> CC: storagedev@microchip.com
> CC: linux-scsi@vger.kernel.org
> CC: Joe Szczypek <jszczype@redhat.com>
> CC: Scott Benesh <scott.benesh@microchip.com>
> CC: Scott Teel <scott.teel@microchip.com>
> CC: Tomas Henzl <thenzl@redhat.com>
> CC: "Martin K. Petersen" <martin.petersen@oracle.com>
> CC: Don Brace <don.brace@microchip.com>
> Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> Suggested-by: Don Brace <don.brace@microchip.com>
> Fixes: f749d8b7a "scsi: hpsa: Correct dev cmds outstanding for retried cmds"
> Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
> ---
> drivers/scsi/hpsa_cmd.h | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/scsi/hpsa_cmd.h b/drivers/scsi/hpsa_cmd.h
> index d126bb877250..617bdae9a7de 100644
> --- a/drivers/scsi/hpsa_cmd.h
> +++ b/drivers/scsi/hpsa_cmd.h
> @@ -20,6 +20,9 @@
> #ifndef HPSA_CMD_H
> #define HPSA_CMD_H
>
> +#include <linux/build_bug.h> /* static_assert */
> +#include <linux/stddef.h> /* offsetof */
> +
> /* general boundary defintions */
> #define SENSEINFOBYTES 32 /* may vary between hbas */
> #define SG_ENTRIES_IN_CMD 32 /* Max SG entries excluding chain blocks */
> @@ -448,11 +451,20 @@ struct CommandList {
> */
> struct hpsa_scsi_dev_t *phys_disk;
>
> - bool retry_pending;
> + int retry_pending;
> struct hpsa_scsi_dev_t *device;
> atomic_t refcount; /* Must be last to avoid memset in hpsa_cmd_init() */
> } __aligned(COMMANDLIST_ALIGNMENT);
>
> +/*
> + * Make sure our embedded atomic variable is aligned. Otherwise we break atomic
> + * operations on architectures that don't support unaligned atomics like IA64.
> + *
> + * Ideally this header should be cleaned up to only mark individual structs as
> + * packed.
> + */
> +static_assert(offsetof(struct CommandList, refcount) % __alignof__(atomic_t) = 0);
> +
> /* Max S/G elements in I/O accelerator command */
> #define IOACCEL1_MAXSGENTRIES 24
> #define IOACCEL2_MAXSGENTRIES 28

I'm seeing this issue as well and without the patch, the kernel won't boot on multiple
ia64 servers. Is there anything that speaks against fixing this?

Thanks,
Adrian

--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
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