From nobody Fri Dec 19 14:37:00 2025 Received: from mail-qt1-f177.google.com (mail-qt1-f177.google.com [209.85.160.177]) (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 498F31D63EE; Mon, 14 Apr 2025 06:01:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.177 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744610493; cv=none; b=tPo6fSwLVIWwUMvNTQvGNmgq4Gm89jRN8lfTreHHpE/yxb847BiyD2MwBJyGIVk25/626QD0c758pEF4UU/QBScYmiSYa6jcvBLVLmy2DoOKTvOKO0mDAU5NZseaH890XAjPsSEuwzxYN5nJ/GBST1PIt8GBu9iFx6oPHbbfB3k= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744610493; c=relaxed/simple; bh=gSFvINbMx+mpurJjbuzYdJO9KVleuEcbzdDZgdWmmk8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=llP4Ffw1UzYoVRfXdq11ZA/yjJo7DCcUWFPJchui2J/5t7Hax9LBuLYEUMMDXaaR5K0dOZKy3aVMHShnhBFBMkhwy/fVwzOsRP/lPqa2+Hl+/FZbPhFBY/4JI8s2MZaNCxmjSXFFJJmkuHYQaXbJBjw8uQOY6aLtzOMnA62nYCg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=eKQXjyFX; arc=none smtp.client-ip=209.85.160.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="eKQXjyFX" Received: by mail-qt1-f177.google.com with SMTP id d75a77b69052e-4774d68c670so56759131cf.0; Sun, 13 Apr 2025 23:01:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1744610491; x=1745215291; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:feedback-id:from:to:cc:subject :date:message-id:reply-to; bh=8yEZCCjAIKX8Bcif/S/pGprjlBDXpto+eqqOQvtfBHY=; b=eKQXjyFXrSCPvnyv1YTcT3o5a9SCJyKmbdV994s5qz0eLxjG/1EJbPrdxeqWWIVdU0 F7mnGFazccSlEJ6M9GxxPtfJMaqaD9TPfVqiTu2gs576kDHm2kms/zVoJGeInFicXhA3 8dRj4vtzfGhKlxHbS8qfzzF/wWzz/VUL17fTxvIWbyuVsftNzVji2AWpFn8VVhqXKgPi b5K/2GZonQO7WbKQqvBTvZi7f3FE4A1MQfp35i5+VOkSsjNOyc4KIL7x8aBbK6+35m7E dII/VjUG9jzD08qh3m8J1+mISJvBCBN/s9UbOK7qMcW91AGE8BbcSvy7ebtnF9abFcfT ww+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1744610491; x=1745215291; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:feedback-id:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=8yEZCCjAIKX8Bcif/S/pGprjlBDXpto+eqqOQvtfBHY=; b=mx3v1YcYt/1Hgop4AowfkPd2+VrKiL8RguJ9/8SY05bt8XZrEc6Yo75lK2/xGRNoEF IICVVLFVY0/065RHEW+PKgnTNUW3jGjSxt3IzmtKTn/MOfiSnR7gj5zzUWfRtDmtPTMO oW1WL1Y5rm3G/e/B1AKN0pC+NVM7d5IlSFajsDx7ENxoxv3/3C0tHJuJ5qwMNi8e2hcz gSdrGmV277Hg2NPCRbqFlmGFlrWbx2rFF1u/pZd/OQPa8KltlknDiuCv3RjlNjL47zSm qVePhNCeOaIAXmhLAf1gFh8SJue0efcbsqzAP4OuAFsOsJlNg6O/YPHcDFIQkmLhxbTl eqhA== X-Forwarded-Encrypted: i=1; AJvYcCUW2hktAFmUcxcPKAXP8Y94vMdyTH855bz3eIEoB2ARJrfJmGN0dTf3i5F9oiebzNOtmcDm@vger.kernel.org, AJvYcCUzyfHmAupOw+s33NcleUnubsG8VVLg4Yr1rMEVzP4kkkCmOzHukl/yrlSICfzHjqDFUicHjLOV@vger.kernel.org, AJvYcCW6rb/313aloITG0NDsRUUugyrJD7PP78uDoAUsVIGU4fMp38lDdUIZQIGiZIyuvXcdyWlnTxPzP7hVdx0=@vger.kernel.org X-Gm-Message-State: AOJu0YyDoYdItgEKpq7qqfjxvjJnYNYSiTZ5MGua6HHuGfYMZVvdlkNr QnWA/9cBUq52ojyZVbW3sHerVC8PsumVc0BnKQttj+73/A5gg2oZ X-Gm-Gg: ASbGncvOULVFHUAHzBZRjE1xipAZp9cRf2Ff3Z/UURmcViLwA1Hm8eWpkply+qnkonX 2QaQ1YCGn9e1hhwlD/bz+A1cSP7LG5q6CdDMyNqiH0dhy1gG5mp1spWvhuOOI/4K7wXS5TNKNuq r7qstTGYefA9BsyQhKAIt0yQqoaPiId0KBokrB31Upec7EpVLrcGyHHY45mdk/sHkq3HiruI9oc UJgEJ7Lm/8KPvjus0KTLkyPw5POIoVxrwhjpGrcJxqBvCJlUu1f9LK/IY/1rVMEANDmcHXViO8N wZasUpnfsN6XgKUZF9K7UHzBkyW/YCGEiChxTJHpcw+swHgvBo++1aZFGEk+dWlvCHi+lCEJaFJ 6wFQpIDn82VbsnT/Jk6sF86CKM1KAwUI= X-Google-Smtp-Source: AGHT+IHDWExJgXvc7ntxhN+BtiblsGHzc2LmReFgtphjkcdAbqKB5qry0e5AfEx4TNIw1Qs3SvIh3g== X-Received: by 2002:a05:622a:1449:b0:476:87f6:3ce4 with SMTP id d75a77b69052e-479775d3200mr175981031cf.39.1744610490778; Sun, 13 Apr 2025 23:01:30 -0700 (PDT) Received: from fauth-a1-smtp.messagingengine.com (fauth-a1-smtp.messagingengine.com. [103.168.172.200]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4796eb15d12sm69685261cf.27.2025.04.13.23.01.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Apr 2025 23:01:30 -0700 (PDT) Received: from phl-compute-06.internal (phl-compute-06.phl.internal [10.202.2.46]) by mailfauth.phl.internal (Postfix) with ESMTP id D4E601200043; Mon, 14 Apr 2025 02:01:29 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-06.internal (MEProxy); Mon, 14 Apr 2025 02:01:29 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgddvudeljeekucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggv pdfurfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpih gvnhhtshculddquddttddmnecujfgurhephffvvefufffkofgjfhgggfestdekredtredt tdenucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrih hlrdgtohhmqeenucggtffrrghtthgvrhhnpefghfffvefhhfdvgfejgfekvdelgfekgeev ueehlefhiedvgeffjefgteeugfehieenucffohhmrghinhepkhgvrhhnvghlrdhorhhgne cuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepsghoqhhu nhdomhgvshhmthhprghuthhhphgvrhhsohhnrghlihhthidqieelvdeghedtieegqdduje ejkeehheehvddqsghoqhhunhdrfhgvnhhgpeepghhmrghilhdrtghomhesfhhigihmvgdr nhgrmhgvpdhnsggprhgtphhtthhopeduledpmhhouggvpehsmhhtphhouhhtpdhrtghpth htoheplhgvihhtrghoseguvggsihgrnhdrohhrghdprhgtphhtthhopehpvghtvghriies ihhnfhhrrgguvggrugdrohhrghdprhgtphhtthhopehmihhnghhosehrvgguhhgrthdrtg homhdprhgtphhtthhopeifihhllheskhgvrhhnvghlrdhorhhgpdhrtghpthhtoheplhho nhhgmhgrnhesrhgvughhrghtrdgtohhmpdhrtghpthhtoheprggvhhesmhgvthgrrdgtoh hmpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdho rhhgpdhrtghpthhtohepnhgvthguvghvsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtg hpthhtohepvgguuhhmrgiivghtsehgohhoghhlvgdrtghomh X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 14 Apr 2025 02:01:29 -0400 (EDT) From: Boqun Feng To: Breno Leitao , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long Cc: aeh@meta.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, edumazet@google.com, jhs@mojatatu.com, kernel-team@meta.com, Erik Lundgren , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Uladzislau Rezki , rcu@vger.kernel.org, Boqun Feng Subject: [RFC PATCH 8/8] locking/lockdep: Use shazptr to protect the key hashlist Date: Sun, 13 Apr 2025 23:00:55 -0700 Message-ID: <20250414060055.341516-9-boqun.feng@gmail.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250414060055.341516-1-boqun.feng@gmail.com> References: <20250414060055.341516-1-boqun.feng@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Erik Lundgren and Breno Leitao reported [1] a case where lockdep_unregister_key() can be called from time critical code pathes where rntl_lock() may be held. And the synchronize_rcu() in it can slow down operations such as using tc to replace a qdisc in a network device. In fact the synchronize_rcu() in lockdep_unregister_key() is to wait for all is_dynamic_key() callers to finish so that removing a key from the key hashlist, and we can use shazptr to protect the hashlist as well. Compared to the proposed solution which replaces synchronize_rcu() with synchronize_rcu_expedited(), using shazptr here can achieve the same/better synchronization time without the need to send IPI. Hence use shazptr here. Reported-by: Erik Lundgren Reported-by: Breno Leitao Link: https://lore.kernel.org/lkml/20250321-lockdep-v1-1-78b732d195fb@debia= n.org/ Signed-off-by: Boqun Feng Reviewed-by: Paul E. McKenney --- kernel/locking/lockdep.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 58d78a33ac65..c5781d2dc8c6 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -58,6 +58,7 @@ #include #include #include +#include =20 #include =20 @@ -1265,14 +1266,18 @@ static bool is_dynamic_key(const struct lock_class_= key *key) =20 hash_head =3D keyhashentry(key); =20 - rcu_read_lock(); + /* Need preemption disable for using shazptr. */ + guard(preempt)(); + + /* Protect the list search with shazptr. */ + guard(shazptr)(hash_head); + hlist_for_each_entry_rcu(k, hash_head, hash_entry) { if (k =3D=3D key) { found =3D true; break; } } - rcu_read_unlock(); =20 return found; } @@ -6614,7 +6619,7 @@ void lockdep_unregister_key(struct lock_class_key *ke= y) call_rcu(&delayed_free.rcu_head, free_zapped_rcu); =20 /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */ - synchronize_rcu(); + synchronize_shazptr(keyhashentry(key)); } EXPORT_SYMBOL_GPL(lockdep_unregister_key); =20 --=20 2.47.1