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Subject[PATCH 4.4 05/48] mm: fix devm_memremap_pages crash, use mem_hotplug_{begin, done}
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@intel.com>

commit f931ab479dd24cf7a2c6e2df19778406892591fb upstream.

Both arch_add_memory() and arch_remove_memory() expect a single threaded
context.

For example, arch/x86/mm/init_64.c::kernel_physical_mapping_init() does
not hold any locks over this check and branch:

if (pgd_val(*pgd)) {
pud = (pud_t *)pgd_page_vaddr(*pgd);
paddr_last = phys_pud_init(pud, __pa(vaddr),
__pa(vaddr_end),
page_size_mask);
continue;
}

pud = alloc_low_page();
paddr_last = phys_pud_init(pud, __pa(vaddr), __pa(vaddr_end),
page_size_mask);

The result is that two threads calling devm_memremap_pages()
simultaneously can end up colliding on pgd initialization. This leads
to crash signatures like the following where the loser of the race
initializes the wrong pgd entry:

BUG: unable to handle kernel paging request at ffff888ebfff0000
IP: memcpy_erms+0x6/0x10
PGD 2f8e8fc067 PUD 0 /* <---- Invalid PUD */
Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
CPU: 54 PID: 3818 Comm: systemd-udevd Not tainted 4.6.7+ #13
task: ffff882fac290040 ti: ffff882f887a4000 task.ti: ffff882f887a4000
RIP: memcpy_erms+0x6/0x10
[..]
Call Trace:
? pmem_do_bvec+0x205/0x370 [nd_pmem]
? blk_queue_enter+0x3a/0x280
pmem_rw_page+0x38/0x80 [nd_pmem]
bdev_read_page+0x84/0xb0

Hold the standard memory hotplug mutex over calls to
arch_{add,remove}_memory().

Fixes: 41e94a851304 ("add devm_memremap_pages")
Link: http://lkml.kernel.org/r/148357647831.9498.12606007370121652979.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/memremap.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -159,7 +159,9 @@ static void devm_memremap_pages_release(
struct page_map *page_map = res;

/* pages are dead and unused, undo the arch mapping */
+ mem_hotplug_begin();
arch_remove_memory(page_map->res.start, resource_size(&page_map->res));
+ mem_hotplug_done();
}

void *devm_memremap_pages(struct device *dev, struct resource *res)
@@ -189,7 +191,9 @@ void *devm_memremap_pages(struct device
if (nid < 0)
nid = numa_mem_id();

+ mem_hotplug_begin();
error = arch_add_memory(nid, res->start, resource_size(res), true);
+ mem_hotplug_done();
if (error) {
devres_free(page_map);
return ERR_PTR(error);

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