The patch titled Subject: mm/kmemleak: avoid scanning potential huge holes has been added to the -mm tree. Its filename is mm-kmemleak-avoid-scanning-potential-huge-holes.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-kmemleak-avoid-scanning-potenti... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-kmemleak-avoid-scanning-potenti...

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------------------------------------------------------ From: Lang Yu lang.yu@amd.com Subject: mm/kmemleak: avoid scanning potential huge holes

When using devm_request_free_mem_region() and devm_memremap_pages() to add ZONE_DEVICE memory, if requested free mem region's end pfn were huge(e.g., 0x400000000), the node_end_pfn() will be also huge (see move_pfn_range_to_zone()). Thus it creates a huge hole between node_start_pfn() and node_end_pfn().

We found on some AMD APUs, amdkfd requested such a free mem region and created a huge hole. In such a case, following code snippet was just doing busy test_bit() looping on the huge hole.

for (pfn = start_pfn; pfn < end_pfn; pfn++) { struct page *page = pfn_to_online_page(pfn); if (!page) continue; ... }

So we got a soft lockup:

watchdog: BUG: soft lockup - CPU#6 stuck for 26s! [bash:1221] CPU: 6 PID: 1221 Comm: bash Not tainted 5.15.0-custom #1 RIP: 0010:pfn_to_online_page+0x5/0xd0 Call Trace: ? kmemleak_scan+0x16a/0x440 kmemleak_write+0x306/0x3a0 ? common_file_perm+0x72/0x170 full_proxy_write+0x5c/0x90 vfs_write+0xb9/0x260 ksys_write+0x67/0xe0 __x64_sys_write+0x1a/0x20 do_syscall_64+0x3b/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae

I did some tests with the patch.

(1) amdgpu module unloaded

before the patch:

real 0m0.976s user 0m0.000s sys 0m0.968s

after the patch:

real 0m0.981s user 0m0.000s sys 0m0.973s

(2) amdgpu module loaded

before the patch:

real 0m35.365s user 0m0.000s sys 0m35.354s

after the patch:

real 0m1.049s user 0m0.000s sys 0m1.042s

Link: https://lkml.kernel.org/r/20211108140029.721144-1-lang.yu@amd.com Signed-off-by: Lang Yu lang.yu@amd.com Acked-by: David Hildenbrand david@redhat.com Acked-by: Catalin Marinas catalin.marinas@arm.com Cc: Oscar Salvador osalvador@suse.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/kmemleak.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/mm/kmemleak.c~mm-kmemleak-avoid-scanning-potential-huge-holes +++ a/mm/kmemleak.c @@ -1410,7 +1410,8 @@ static void kmemleak_scan(void) { unsigned long flags; struct kmemleak_object *object; - int i; + struct zone *zone; + int __maybe_unused i; int new_leaks = 0;

jiffies_last_scan = jiffies; @@ -1450,9 +1451,9 @@ static void kmemleak_scan(void) * Struct page scanning for each node. */ get_online_mems(); - for_each_online_node(i) { - unsigned long start_pfn = node_start_pfn(i); - unsigned long end_pfn = node_end_pfn(i); + for_each_populated_zone(zone) { + unsigned long start_pfn = zone->zone_start_pfn; + unsigned long end_pfn = zone_end_pfn(zone); unsigned long pfn;

for (pfn = start_pfn; pfn < end_pfn; pfn++) { @@ -1461,8 +1462,8 @@ static void kmemleak_scan(void) if (!page) continue;

- /* only scan pages belonging to this node */ - if (page_to_nid(page) != i) + /* only scan pages belonging to this zone */ + if (page_zone(page) != zone) continue; /* only scan if page is in use */ if (page_count(page) == 0) _

Patches currently in -mm which might be from lang.yu@amd.com are

mm-kmemleak-avoid-scanning-potential-huge-holes.patch