On Fri, Nov 05, 2021 at 02:14:50PM +0100, David Hildenbrand wrote:
> 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., 0x400000000 ,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;
The original code has covered that, i.e.,
only scan pages belonging to this node.
I didn't change that behavior.
Thanks,
Lang
> --
> Thanks,
>
> David / dhildenb
>
