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 B05462405E8; Thu, 16 Oct 2025 23:23:25 +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=1760657005; cv=none; b=fylNYSEp7kG5j/UHSROrou/y0awtISgrV4fAyVTrcQRiBTlGNDIg6z78TpTM4EIHsviJxD/jda30awWZ/mAGXyOz7GjfJCoyoO9FaroNnPH4VdAFEibrpHNHJC6KmKZY52WaZ06MuQKhszI74RS31Odw+R/3ja/7fJz6EzNGMgY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760657005; c=relaxed/simple; bh=AoOr6NzAAERUS6WMCz640DwHNaOlipYNbvxIeaLPK2c=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=UQnAAmojmLkAmQvi0b7/6HLfQXXG6T9UeMCl8Mt95vDQVM3W7MIrIp8cL9gith555Alg0aNvKz1Pph0NqQc5rBFDIbwC+ZBjKwahuKcnzkDzwRhYVvrOHeDM2Q5nRiM0a9Uzz3EOscQr8yAMmWFB/64v8eVpTAyXKT7QiZIfdaQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZUFJ9UAX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZUFJ9UAX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D79B0C4CEF1; Thu, 16 Oct 2025 23:23:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760657005; bh=AoOr6NzAAERUS6WMCz640DwHNaOlipYNbvxIeaLPK2c=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ZUFJ9UAXp1v5Idy/X+tlbirueHIm1S9bVyj3YC9uodEUSTVQ+RFRz2adyXxHnUDU+ TiAF2zFPYV5/ClDoSAX363LrZr63/ZljaLmzi9cLXjrNBExZLXSRBGqCcLVEJRRcZS hA3rTPKPg2O9Wil92qdxo945DOOTyhL4tljn9iGfNdqZ+kGfy8LnKwKR9AEX6vBPgm tA5w0LCCy/WOsYLrtayuQMCF8o2P4GklOsjln6eyNB8kn2Rpbovc6yoMMewvjg+4Oc RJSoKynnEaM1Fz6P5esuqtgnlenR5Pzw7zJcIndpuhNiFpOY9N5spKyLYPfo0eHySF gbzPA8S+YSWkw== Date: Thu, 16 Oct 2025 16:23:23 -0700 From: Jakub Kicinski To: Breno Leitao Cc: "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH net v3] netpoll: Fix deadlock in memory allocation under spinlock Message-ID: <20251016162323.176561bd@kernel.org> In-Reply-To: <20251014-fix_netpoll_aa-v3-1-bff72762294e@debian.org> References: <20251014-fix_netpoll_aa-v3-1-bff72762294e@debian.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 14 Oct 2025 09:37:50 -0700 Breno Leitao wrote: > + while (1) { > + spin_lock_irqsave(&skb_pool->lock, flags); > + if (skb_pool->qlen >= MAX_SKBS) > + goto unlock; > + spin_unlock_irqrestore(&skb_pool->lock, flags); No need for the lock here: if (READ_ONCE(..) >= MAX_SKBS) > skb = alloc_skb(MAX_SKB_SIZE, GFP_ATOMIC); > if (!skb) > - break; > + return; > > + spin_lock_irqsave(&skb_pool->lock, flags); > + if (skb_pool->qlen >= MAX_SKBS) > + /* Discard if len got increased (TOCTOU) */ > + goto discard; Not sure this is strictly needed, the number 32 (MAX_SKBS) was not chosen super scientifically anyway, doesn't matter if we go over a little. But if we care I think we can: if (skb_pool->qlen < MAX_SKBS) __skb_queue_tail(skb_pool, skb); else dev_kfree_skb_any(skb); and there's no need for the gotos > __skb_queue_tail(skb_pool, skb); > + spin_unlock_irqrestore(&skb_pool->lock, flags); > } -- pw-bot: cr