From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F01EF373BFC for ; Sat, 4 Apr 2026 05:36:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775281006; cv=none; b=tK+4bm//3ZDjPRXsnmdoBHtUTN9cGVSo/EcmqeGHu6X37UorJWvkdfnK6SJrr2n3lStWYjanvd6RC039R+OxuSbQkQxIPZa1Tp9NRJ5MpawzBN7fCANBgbXpnrEAqTXeY+EsEiEok+vQldailIGsWS5Eg7pUCtX4YkeWbr56fMg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775281006; c=relaxed/simple; bh=DSLfSyHQj1/pfjJ0/flR1vfGkic31tLO0vddP3e0HBQ=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=suLhGWMevcBV7EjcclDUH0b2fMAjyve7b7CUcIkzADXf1QkZ/tZI6DhnqlWW3lNsdr44UmVaWwUmnCMYgKe8/HKNsn0qmhaLmB+Pj+Aq3LZuZLuPpT5CXkCCwq7apIA0yook+2qCuRtwcNEN66jCiNwhBhFa6JhhH6p1RstH9Xs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=NgWjB2F1; arc=none smtp.client-ip=209.85.214.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="NgWjB2F1" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2b0c92ff4ebso31474255ad.2 for ; Fri, 03 Apr 2026 22:36:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1775281004; x=1775885804; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=ds56DNff610cUML0mVwRrV+nM7vhJRfBIMktQ5hdFtQ=; b=NgWjB2F1t2rEXDjzChiqTLNvX81kGeUA6o35dWi/w2mA29JQRvG6uut4+g2gz2sAIQ 3zlkg8aeK3UHSQj1UTQxDH0TnDvxxf8FFuUQJohVFQY8nIRJuICUbqMC2hEfBWUxubUQ qu9m63zC/z8nPd27UWexcXUYr2U+Wpy0kkMwYrsb+1qk0F0EABiVdcPxcHcbDEHdOCXH Qwl3tY3K0Z4+JBTl3t6odxWOGcifZaKawIpSWjLXDVyy/ysBDP4FWDcIU6p7zZZs+Ged DulOW6YyiaauTfOU8BpMkc6WyrVca/maIxUiQdbfqDUbIZM9uzlcLliM9BDgyrWDEDLd 6Jew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1775281004; x=1775885804; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ds56DNff610cUML0mVwRrV+nM7vhJRfBIMktQ5hdFtQ=; b=GTmK42z5d77LhzqW6hlglhwuWa7JCVoVJY34n1lSSgGe/4HV8wmLbD6WSNRHR0VL8f yhRGUtGfDgeR0v3zyX7iW5Gi321TM4nE0E0oYq6XJH+YIVSGT3y6ccK/XB8wBn4WwZWS p5aZa2vGVar9HtrZuvInshFPSOOFL95Z3BmSm9EvsOx5hCMc6UaTEMMEeHjoCx36p2fF QdlIO4aDaPDe6mY6avCeny58HVcPrXJH53lwvn5mmTwIRURj9QypOPJHyWLAjuYYk70U 0LAWeYWyQpWVDwSFtxCjhDHKgQQxrkivlT2PiWUnbD+C10RuidY6d1fwTGu2rCMrBZSL 63Lw== X-Gm-Message-State: AOJu0YwBPFJMmebXAsngI4sDxXzWGUloY2WS3YU0WxgFDp/WHpj5GjtO xbW9qn9Ky09BJRJ4/DVxenscJ5Wz4DdSbF9F0IDZ851NPo225vYz0pQ3YhKR9nLRi6gQMHtmJDp tSXbBhmn3LeS+A5xAS/Exz2eY7HgPMn3jQ0ik4UY8cUzkl7jYWmaV/d7cDh9qMrF3CDbtWwQCS0 YqBchE/dE87o2a5HRy1ilnJYR9Im41b3XuiHUqiMacIZx+PJbB X-Received: from pgkb17.prod.google.com ([2002:a63:eb51:0:b0:c76:6a98:b776]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7348:b0:39b:9644:6ea4 with SMTP id adf61e73a8af0-39f2ee63d6dmr5395232637.16.1775281003685; Fri, 03 Apr 2026 22:36:43 -0700 (PDT) Date: Sat, 4 Apr 2026 05:36:19 +0000 In-Reply-To: <20260404053632.1729280-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260404053632.1729280-1-jstultz@google.com> X-Mailer: git-send-email 2.53.0.1213.gd9a14994de-goog Message-ID: <20260404053632.1729280-3-jstultz@google.com> Subject: [PATCH v27 02/10] sched: Avoid donor->sched_class->yield_task() null traversal From: John Stultz To: LKML Cc: John Stultz , Joel Fernandes , Qais Yousef , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Mel Gorman , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kuyo chang , hupu , kernel-team@android.com Content-Type: text/plain; charset="UTF-8" With proxy-exec once we do return migration from ttwu(), if a task is proxying for a waiting donor, and the donor is woken up, we switch the rq->donor to point to idle briefly until we can re-enter __schedule(). However, if a task that was acting as a proxy calls into yield() right after the donor is switched to idle, it may trip a null pointer traversal, because the idle task doesn't have a yield_task() pointer. So add a conditional to ensure we don't try to call the yield_task() pointer in that case. This was only recently found because prior to commit 127b90315ca07 ("sched/proxy: Yield the donor task") do_sched_yield() incorrectly called current->sched_class_yield_task() instead of using rq->donor. Signed-off-by: John Stultz --- Cc: Joel Fernandes Cc: Qais Yousef Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Steven Rostedt Cc: Ben Segall Cc: Zimuzo Ezeozue Cc: Mel Gorman Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Cc: "Paul E. McKenney" Cc: Metin Kaya Cc: Xuewen Yan Cc: K Prateek Nayak Cc: Thomas Gleixner Cc: Daniel Lezcano Cc: Suleiman Souhlal Cc: kuyo chang Cc: hupu Cc: kernel-team@android.com --- kernel/sched/syscalls.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index b215b0ead9a60..e3e4fd674ed63 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -1340,7 +1340,8 @@ static void do_sched_yield(void) rq = this_rq_lock_irq(&rf); schedstat_inc(rq->yld_count); - rq->donor->sched_class->yield_task(rq); + if (rq->donor->sched_class->yield_task) + rq->donor->sched_class->yield_task(rq); preempt_disable(); rq_unlock_irq(rq, &rf); -- 2.53.0.1213.gd9a14994de-goog