From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1B0A3FBF2; Sat, 3 Feb 2024 04:11:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706933511; cv=none; b=jSFSZeLWfZQfPYI+OyEqt47D2kn3sAKGuep0fOdtqWbVsKr0enEEwFR/8K06nli/BZVAFQar/x2RGcWlimEzMUEYlQy3Tqd4MnDBVIPVOOb4CruO54Ubyd3oKzZcTrO/A0wen45VpMep0TxKgxAPlY32AH4x6egrcg/9TU3igIo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706933511; c=relaxed/simple; bh=ck9X6CuWtItL+1gMrn+Qcy+1H93JIf7m63831EoFgAE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=avdp4nSeOYpZd+JYCND23B/owI0YTchp+EYD4hR95lL10GoPP9DwuVEceqW6RP97atXWQvMqxffwtizTHazCd3hwfRXIdi2z1YkQ8KPjCJfBwm1Gj+CmorJWm7iHlImwScmCKIm8tw1TxsjDi9ug9qGKxGrzvaH7RCboZjAf80g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MkRi32sQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="MkRi32sQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA096C433F1; Sat, 3 Feb 2024 04:11:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1706933510; bh=ck9X6CuWtItL+1gMrn+Qcy+1H93JIf7m63831EoFgAE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MkRi32sQF143wSPZcpeKOGfxG+Lkmx+1OICLbNYk1V++r3zU5qB5DDhaftjH/PGlh ReMejc5gOiH4wCOpo2VVPrJcNaYao7MauigGSMIhLZMwfMcCKWoe9HxWh7aHcyfNNA UjYMwZ5Laojc2N2uHDC1gpVF78Qx9BURqPYuP1WA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleg Nesterov , David Howells , Marc Dionne , linux-afs@lists.infradead.org, Sasha Levin Subject: [PATCH 6.6 039/322] afs: fix the usage of read_seqbegin_or_lock() in afs_lookup_volume_rcu() Date: Fri, 2 Feb 2024 20:02:16 -0800 Message-ID: <20240203035400.346869940@linuxfoundation.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240203035359.041730947@linuxfoundation.org> References: <20240203035359.041730947@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov [ Upstream commit 4121b4337146b64560d1e46ebec77196d9287802 ] David Howells says: (2) afs_lookup_volume_rcu(). There can be a lot of volumes known by a system. A thousand would require a 10-step walk and this is drivable by remote operation, so I think this should probably take a lock on the second pass too. Make the "seq" counter odd on the 2nd pass, otherwise read_seqbegin_or_lock() never takes the lock. Signed-off-by: Oleg Nesterov Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org Link: https://lore.kernel.org/r/20231130115606.GA21571@redhat.com/ Signed-off-by: Sasha Levin --- fs/afs/callback.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/afs/callback.c b/fs/afs/callback.c index a484fa642808..90f9b2a46ff4 100644 --- a/fs/afs/callback.c +++ b/fs/afs/callback.c @@ -110,13 +110,14 @@ static struct afs_volume *afs_lookup_volume_rcu(struct afs_cell *cell, { struct afs_volume *volume = NULL; struct rb_node *p; - int seq = 0; + int seq = 1; do { /* Unfortunately, rbtree walking doesn't give reliable results * under just the RCU read lock, so we have to check for * changes. */ + seq++; /* 2 on the 1st/lockless path, otherwise odd */ read_seqbegin_or_lock(&cell->volume_lock, &seq); p = rcu_dereference_raw(cell->volumes.rb_node); -- 2.43.0