From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EBD4C3955FF for ; Thu, 3 Sep 2026 18:27:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788460028; cv=none; b=krNkS0EzcpPwKazl7qygCTHRZTBaFdPSRoa+4wSlR4Fi7qWVxRKEG9+U2TDaHRCYKwmr+epMTkz5bSqhyC3m3Gq6mmOpxTAONwL1saxAz4N4zYZiJ0b4AiFkoqFnjY66nD7aJBF3J3cNVtDhj0FGBLzHu+JZJXVpDsz6gFWESdk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788460028; c=relaxed/simple; bh=fp8PVJld42kEIOP9kwG5WGfSPK24k3mgfP+SAjpHtwU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dKK6WAEIW/mEnBJ6bEl136pdK9iZb2jXe4OUYZEBqpfUzAt57f5W54S4cDb6ARmz9gO0oVU8340flcs9a8bwAADeNr18rI2NUbY1X8lCXlV5skS1YbzF/YzTH6Bhb5pWctmbagXoDye+kLGNDd4BB+EOheF1FLR7etyZB7KhWgc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OFUw+d9f; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OFUw+d9f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE7AD1F00ACF; Thu, 3 Sep 2026 18:27:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788460021; bh=2pgoGUu8YthfU+kaufNg4EhN3jcejJX2TjkSP7w0b9I=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=OFUw+d9fARxd2FH6jYUay78LsdTzglzMOY+exSVaxiXxymi1+gCf33Zp3w33vjn/N AfNRO6lWdIjpJ/lfuWaFbYzAy3xcsArvPlSVl+ypWNGVeblb484HjqH4vIeJLuXc7m esiA0pJQdSojI67cSQBVpl1RHKXV7YEvchCjFQRy+DphDESxg35l8Wck7dt3mYglfO ++pxT+KCzyQofSH+ej/JIZPWQQMPVKtjESs5yTaq+AZkGliv5cZioHQx/or7GZclfI J8H8idmHUqCb13kIdkOT6BRiEvYm5W2Y5QMt0BgAw9ryBp0vmPIfSfKus36X8ZyFbo 3oDQ+tmDzf+ug== From: Sasha Levin To: stable@vger.kernel.org Cc: Breno Leitao , "Paul E. McKenney" , SJ Park , Catalin Marinas , Puranjay Mohan , Andrew Morton , Sasha Levin Subject: [PATCH 6.18.y 2/2] mm/kmemleak: report RCU-tasks quiescent states during the scan Date: Thu, 3 Sep 2026 14:26:58 -0400 Message-ID: <20260903182658.1452185-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260903182658.1452185-1-sashal@kernel.org> References: <2026090344-parted-gnarly-5282@gregkh> <20260903182658.1452185-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Breno Leitao [ Upstream commit 3541a2b06ecd78ba333188df04368dcf97273d6a ] 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 b96285e10aad ("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: c4b28963fd79 ("mm/kmemleak: rely on rcu for task stack scanning") Signed-off-by: Breno Leitao Reviewed-by: Paul E. McKenney Reviewed-by: SJ Park Reviewed-by: Catalin Marinas Cc: Breno Leitao Cc: Puranjay Mohan Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/kmemleak.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 5109a9f84ea50..b4a7ed2116353 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1564,7 +1564,7 @@ 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; @@ -1601,7 +1601,7 @@ 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; @@ -1623,7 +1623,7 @@ 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 { @@ -1651,7 +1651,7 @@ 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()) @@ -1686,7 +1686,7 @@ 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); @@ -1731,7 +1731,7 @@ static void kmemleak_scan_task_stacks(void) } put_task_struct(p); } - cond_resched(); + cond_resched_tasks_rcu_qs(); } while (pid && !stop); } @@ -1810,7 +1810,7 @@ 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; -- 2.53.0