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mm/memory-failure: fix detection of memory_failure() handlers

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.

Link: https://lkml.kernel.org/r/166153428781.2758201.1990616683438224741.stgit@dwillia2-xfh.jf.intel.com
Fixes: 33a8f7f2b3a3 ("pagemap,pmem: introduce ->memory_failure()")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Dan Williams and committed by
Andrew Morton 65d3440e fd63612a

+6 -1
+5
include/linux/memremap.h
··· 139 139 }; 140 140 }; 141 141 142 + static inline bool pgmap_has_memory_failure(struct dev_pagemap *pgmap) 143 + { 144 + return pgmap->ops && pgmap->ops->memory_failure; 145 + } 146 + 142 147 static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap) 143 148 { 144 149 if (pgmap->flags & PGMAP_ALTMAP_VALID)
+1 -1
mm/memory-failure.c
··· 1928 1928 * Call driver's implementation to handle the memory failure, otherwise 1929 1929 * fall back to generic handler. 1930 1930 */ 1931 - if (pgmap->ops->memory_failure) { 1931 + if (pgmap_has_memory_failure(pgmap)) { 1932 1932 rc = pgmap->ops->memory_failure(pgmap, pfn, 1, flags); 1933 1933 /* 1934 1934 * Fall back to generic handler too if operation is not