On Fri, Aug 26, 2022 at 10:18:07AM -0700, Dan Williams wrote:
> Some pagemap types, like MEMORY_DEVICE_GENERIC (device-dax) do not even
> have pagemap ops which results in crash signatures like this:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000010
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 8000000205073067 P4D 8000000205073067 PUD 2062b3067 PMD 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 22 PID: 4535 Comm: device-dax Tainted: G OE N 6.0.0-rc2+ #59
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> RIP: 0010:memory_failure+0x667/0xba0
> [..]
> Call Trace:
> <TASK>
> ? _printk+0x58/0x73
> do_madvise.part.0.cold+0xaf/0xc5
>
> Check for ops before checking if the ops have a memory_failure()
> handler.
>
> Fixes: 33a8f7f2b3a3 ("pagemap,pmem: introduce ->memory_failure()")
> Cc: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
> Cc: Jane Chu <jane.chu@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Cc: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Thank you for sending patches, this looks fine to me.
Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> ---
> include/linux/memremap.h | 5 +++++
> mm/memory-failure.c | 2 +-
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 19010491a603..c3b4cc84877b 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -139,6 +139,11 @@ struct dev_pagemap {
> };
> };
>
> +static inline bool pgmap_has_memory_failure(struct dev_pagemap *pgmap)
> +{
> + return pgmap->ops && pgmap->ops->memory_failure;
> +}
> +
> static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
> {
> if (pgmap->flags & PGMAP_ALTMAP_VALID)
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 14439806b5ef..8a4294afbfa0 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1928,7 +1928,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> * Call driver's implementation to handle the memory failure, otherwise
> * fall back to generic handler.
> */
> - if (pgmap->ops->memory_failure) {
> + if (pgmap_has_memory_failure(pgmap)) {
> rc = pgmap->ops->memory_failure(pgmap, pfn, 1, flags);
> /*
> * Fall back to generic handler too if operation is not
