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Subject[PATCH] mm/kmemleak: Avoid scanning potential huge holes
Date
When using devm_request_free_mem_region() and
devm_memremap_pages() to add ZONE_DEVICE memory, if requested
free mem region pfn were huge(e.g., 0x0x400000000 ,we found
on some amd apus, amdkfd svm will request a such free mem region),
the node_end_pfn() will be also huge(see move_pfn_range_to_zone()).
It creates a huge hole between node_start_pfn() and node_end_pfn().

In such a case, following code snippet acctually 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

Signed-off-by: Lang Yu <lang.yu@amd.com>
---
mm/kmemleak.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index b57383c17cf6..d07444613a84 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1403,6 +1403,7 @@ static void kmemleak_scan(void)
{
unsigned long flags;
struct kmemleak_object *object;
+ struct zone *zone;
int i;
int new_leaks = 0;

@@ -1443,9 +1444,9 @@ 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++) {
@@ -1455,7 +1456,7 @@ static void kmemleak_scan(void)
continue;

/* only scan pages belonging to this node */
- if (page_to_nid(page) != i)
+ if (page_to_nid(page) != zone_to_nid(zone))
continue;
/* only scan if page is in use */
if (page_count(page) == 0)
--
2.25.1
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