github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-09-22 12:44:03 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

mm/kmemleak: report RCU-tasks quiescent states during the scan

Browse Source 
kmemleak_scan() can run for ages on large debug kernels. It was
causing some soft-lockups which I got fixed with commit
3175fcfec8b16baeb ("mm/kmemleak: avoid soft lockup when scanning task
stacks") with our beloved cond_resched().

I've got the fix above deployed in the Meta fleet, and now I am seeing:

  INFO: rcu_tasks detected stalls on tasks:
    task:kmemleak state:R ... nvcsw: 274/274 holdout: 1 idle_cpu: -1/3
     scan_block
     scan_gray_list
     kmemleak_scan

and, worse, blocks the callers waiting on that grace period.  Here a BPF
struct_ops map free, which waits via synchronize_rcu_mult(call_rcu,
call_rcu_tasks), is stuck long enough to also trip the hung task check:

  INFO: task kworker/...:bpf_map_free_deferred blocked for 122 seconds
     __wait_rcu_gp
     bpf_struct_ops_map_free

Then I've learned that cond_resched() is not an RCU-tasks quiescent
state, so, we need to use stronger primitives.

Use cond_resched_tasks_rcu_qs() at the scan reschedule points so the scan
reports an RCU-tasks quiescent state as it proceeds.

Inspired by commit b96285e10a ("tracing: Have osnoise_main() add a
quiescent state for task rcu").

Link: https://lore.kernel.org/20260720-kmemleak_rcu_task-v1-1-5b460ade777d@debian.org
Fixes: c4b28963fd ("mm/kmemleak: rely on rcu for task stack scanning")
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Puranjay Mohan <puranjay@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Breno Leitao 2026-07-20 06:23:45 -07:00 committed by Andrew Morton
parent fb580e1964
commit 3541a2b06e
1 changed files with 7 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
mm/kmemleak.c
View File

@ -1571,7 +1571,7 @@ static int scan_large_block(void *start, void *end)
if (scan_block(start, next, NULL))
return 1;
start = next;
cond_resched();
cond_resched_tasks_rcu_qs();
}
return 0;
@ -1608,7 +1608,7 @@ static void scan_object(struct kmemleak_object *object)
scan_block(start, end, object);
raw_spin_unlock_irqrestore(&object->lock, flags);
cond_resched();
cond_resched_tasks_rcu_qs();
raw_spin_lock_irqsave(&object->lock, flags);
if (!(object->flags & OBJECT_ALLOCATED))
break;
@ -1630,7 +1630,7 @@ static void scan_object(struct kmemleak_object *object)
break;
raw_spin_unlock_irqrestore(&object->lock, flags);
cond_resched();
cond_resched_tasks_rcu_qs();
raw_spin_lock_irqsave(&object->lock, flags);
} while (object->flags & OBJECT_ALLOCATED);
} else {
@ -1658,7 +1658,7 @@ static void scan_gray_list(void)
*/
object = list_entry(gray_list.next, typeof(*object), gray_list);
while (&object->gray_list != &gray_list) {
cond_resched();
cond_resched_tasks_rcu_qs();
/* may add new objects to the list */
if (!scan_should_stop())
@ -1693,7 +1693,7 @@ static void kmemleak_cond_resched(struct kmemleak_object *object)
raw_spin_unlock_irq(&kmemleak_lock);
rcu_read_unlock();
cond_resched();
cond_resched_tasks_rcu_qs();
rcu_read_lock();
raw_spin_lock_irq(&kmemleak_lock);
@ -1738,7 +1738,7 @@ static void kmemleak_scan_task_stacks(void)
}
put_task_struct(p);
}
cond_resched();
cond_resched_tasks_rcu_qs();
} while (pid && !stop);
}
@ -1915,7 +1915,7 @@ static void kmemleak_scan(void)
struct page *page = pfn_to_online_page(pfn);
if (!(pfn & 63))
cond_resched();
cond_resched_tasks_rcu_qs();
if (!page)
continue;