On 05.11.21 04:52, Lang Yu wrote:
> 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@xxxxxxx>
> ---
> 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))
With overlapping zones you might rescan ranges ... instead we should do:
/* only scan pages belonging to this zone */
if (zone != page_zone(page))
...
Or alternatively:
/* only scan pages belonging to this node */
if (page_to_nid(page) != zone_to_nid(zone))
continue;
/* only scan pages belonging to this zone */
if (page_zonenum(page) != zone_idx(zone))
continue;
--
Thanks,
David / dhildenb
